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Essential osh revised 2706 final


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Essential osh revised 2706 final

  1. 1. Essential, primary preventive, occupational safety and health interventions for low and middle income countries Evidence Report Jos VerbeekFinnish Institute of Occupational HealthCochrane Occupational Safety and Health Review GroupPO Box 31070701 KuopioFinlande-mail: jos.verbeek@ttl.fitel: +358-46-8108709 1
  2. 2. Contents1. Introduction .................................................................................................................................................................. 42. Methods ......................................................................................................................................................................... 4 From burden of occupational diseases and injuries to exposure .................................................................................. 6 Work-related cancer and its related exposure ............................................................................................................. 7 Pneumoconiosis and related exposures ....................................................................................................................... 8 Chronic Obstructive Pulmonary Disease and related exposures................................................................................. 8 Occupational Asthma and related exposures ............................................................................................................... 9 Noise induced hearing loss and related noise exposure .............................................................................................. 9 Back Pain and related biomechanical exposure .......................................................................................................... 9 Injuries and related exposure to hazardous situations .............................................................................................. 10 From exposure to preventive interventions ................................................................................................................ 113. Evidence of effectiveness of occupational health interventions .............................................................................. 14 3.1 Interventions for decreasing inhalation exposure ................................................................................................. 14 Environmental interventions: substitution ....................................................................................................... 14 Environmental interventions: other control measures ...................................................................................... 15 Environmental measures: regulation and other incentives ............................................................................... 18 Behavioural: respiratory protection for preventing inhalation exposure .......................................................... 18 Clinical: pre-employment examinations and drugs .......................................................................................... 18 3.2 Interventions for decreasing exposure to noise .................................................................................................... 19 Environmental interventions ............................................................................................................................ 20 Behavioural interventions: promotion of hearing protection ........................................................................... 20 Clinical interventions ....................................................................................................................................... 21 3.3 Interventions for decreasing biomechanical exposure ......................................................................................... 21 Environmental interventions: load reduction and ergonomics ......................................................................... 22 Behavioural interventions: education and training .......................................................................................... 22 Clinical interventions: pre-employment examinations .................................................................................... 23 3.4 Interventions for prevention of injuries ................................................................................................................ 23 Environmental interventions ............................................................................................................................ 23 Prevention of injuries in agriculture and construction industry ....................................................................... 25 Behavioural interventions: Occupational Safety Training ............................................................................... 26 Behavioural safety interventions: feedback and rewards ................................................................................. 27 Clinical: Pre-employment examinations for preventing injuries ..................................................................... 28 3.5. Approaches to Small Enterprises ........................................................................................................................ 284. Conclusions and discussion ........................................................................................................................................ 298. References.................................................................................................................................................................... 359. Appendices .................................................................................................................................................................. 40 2
  3. 3. Executive SummaryThere is still a considerable global burden of occupational diseases and injuries that leads to many fatalitieseach year. It is not well known which interventions can effectively reduce the exposures at work whicheventually cause these occupational diseases and injuries. The objective of this report is to provide theavailable evidence from systematic reviews of essential preventive interventions that can reduce the globalburden of occupational diseases and injuries.Essential interventions are interventions that reduce most of the global burden of occupational disease andinjuries. These interventions should therefore aim to reduce the incidence of work-related cancer, dust-related diseases, occupational asthma, COPD, noise-induced hearing loss, back pain and occupationalinjuries. Primary prevention of those diseases occurs through reduction of the exposures that lead to thesediseases. These interventions are categorised as environmental, behavioural and clinical. The literature wassearched to locate systematic reviews of interventions that can reduce each of these exposures through any ofthese interventions.The evidence available in these systematic reviews shows that there are many technical measures to reduceexposure available that can have a major impact on the global burden of work-related cancer, dust-relateddiseases, asthma, COPD, noise and injuries. However, to effectuate this potential, better implementation isneeded. This can be realised by better regulation, reinforcement or incentives for employers. Feedback andrewards for workers probably help in reducing occupational injuries. However, the available systematicreviews do not provide evidence that back pain can be prevented. Personal protective equipment also hastechnical potential to reduce exposure but without proper use and instruction this can not be realised. On thecontrary, there is no evidence in the available reviews that education and training reduce occupationaldisease and injuries. Clinical interventions such as drugs and health examinations have little to offer forprimary prevention of occupational diseases and injuries.More and better systematic reviews are needed to enable a better overview of the evidence especially in thearea of injury prevention.AcknowledgementsI am grateful to Irja Laamanen and Leena Isotalo, information specialists at FIOH for helping me with thesearching of systematic reviews 3
  4. 4. 1. IntroductionExperts estimate that less than 15% of the global workforce has some coverage with occupational healthservices.1 The 60th World Health Assembly in 2007 urged the 193 Member States of WHO to work towardsfull coverage with essential interventions and basic occupational health services, particularly in agriculture,small and medium size enterprises, informal economy, and migrant workers. WHO was requested to provideguidance to countries on basic packages, tools, working methods and models of good practices foroccupational health services and to stimulate international efforts for capacity building as part of the GlobalPlan of Action on Workers Health 2008‐2017.2The range of the interventions to prevent occupational and work‐related diseases and injuries may includeboth clinical (e.g. health examinations) and non‐clinical interventions (e.g. workplace risk assessment). Theinterventions can be categorised as primary preventive interventions and treatment interventions. Primarypreventive interventions aim at preventing disease or injury outcomes before the disease or injury processhas started. In occupational health, this means usually that efforts are directed at decreasing exposure knownto be hazardous to health. Providers of such interventions may include health practitioners in clinical settingssuch as primary care centres, non‐clinical providers such as workers representatives and employeesresponsible for health and safety in the enterprise or occupational hygiene and safety experts in specializedoccupational health services.Many countries have already in place some form of basic occupational health services to deliver essentialinterventions for the prevention of occupational and work‐related diseases and injuries 1. However, it is notwell known what evidence exists for the effectiveness of these interventions. To be better able to developguidance on essential primary preventive occupational health and safety interventions this evidence isneeded. WHO is especially interested in evidence for essential interventions in basic occupational healthservices targeted at underserved working populations with constrained resources and integrated in primaryhealth care. The first step in this process of guidance development is to locate systematic reviews that havesynthesised the evidence available from primary studies.Based on available systematic reviews, I report here what is the evidence for the effectiveness of the mostessential occupational health interventions for primary prevention of work‐related diseases and injuries inagriculture, small and medium sized enterprises and the informal economy across WHO regions.2. Methods 4
  5. 5. To answer this policy and research question I will first further define essential occupational healthinterventions for primary prevention of occupational diseases and injuries. These essential interventionsshould prevent occupational diseases and injuries in underserved populations with constrained resources. Themechanism behind such interventions is that they cut the causal chain between exposure at work and theresulting occupational disease or injury (figure 1).3 Basically, occupational health interventions can becategorised into three major classes: environmental, behavioural and clinical. Environmental interventionsaim at changing the working environment in order to eliminate the exposure in a technical sense.Behavioural interventions focus on individual workers behaviour to eliminate exposure such as increasingthe use of personal protective equipment. Clinical interventions use a clinical method to prevent disease suchas vaccination. Even though other preventive methods are available such as screening or early diagnosis, Iwill not take these into consideration because I will focus entirely on primary prevention. Environmental interventions Behavioural Interventions Clinical Interventions Interventions: Interventions: Interventions: E.g Work-site visits. E.g. Health E.g.Treatment Organisational promotion. Counselling changes. Regulation. Education. Reward- Vaccination Technical changes: punishment. substitution, Personal protective ventilation. equipment Worker Health Behaviour Risk factor at work Disease, Disability, Injury Verbeek, Scand J WEH 2004 figure 1: Model of occupational health interventionsI consider those interventions as essential that aim at eliminating exposures with the biggest impact on thetarget population. The WHO has examined the global burden of occupational disease in a recent project.4 Itook the diseases and injuries that are mentioned in this report as the point of departure. Next, I determinedwhich exposure lead to these diseases and injuries. This resulted in a limited list of exposures that should beaddressed by essential interventions. 5
  6. 6. In the next step, I looked for evidence of effectiveness of essential interventions as generated by evaluationresearch and reported in the literature. Since it would be impossible to look for all primary studies on allexposures and interventions I searched only for evidence at an aggregated level in the form of systematicreviews. I defined systematic reviews as reviews of the literature that had a clearly formulated question andsearched electronic databases. I combined search strategies for finding occupational safety and healthintervention studies with search strategies for finding systematic reviews. For locating occupational safetyand health intervention studies, I used the search strategy developed by the Cochrane Occupational HealthField 1 and for locating systematic reviews I used the search strategy developed by the Perosh SystematicClearing House Working Group ( In principle, I did not search for primary studies whenthere were no systematic reviews available. I searched first in Medline through Pubmed and then in Embasethrough OvidSP to see if any additional systematic reviews could be found.I explicitly did not review the literature on secondary prevention, treatment or rehabilitation. Even thoughthere are many effective and essential interventions that address rehabilitation issues and that could becarried out in a low-resource setting, these are not included because this project only addresses primaryprevention.From burden of occupational diseases and injuries to exposureTable 1 provides an overview of the essential occupational diseases and injuries with a big impact on thetarget population derived from the global burden of disease project.4;5 The target group of the essentialoccupational health interventions consists of workers in small businesses in low and middle income countriesespecially in agriculture and the so-called informal sector. Work-related disorder to be prevented Risk factors to be addressed 1. Work-related Cancer Arsenic, asbestos, berylium, cadmium, chromium, diesel exhaust, nickel, silica, benzene, ionizing radiation, ethelyne oxide 2. Asthma Biological agents: grains, flours, plants, gums, fur, feathers, insects, fungi, drugs, woods chemical agents: chlorofluorocarbons, alcohols, metals, welding fumes 3. COPD Non-specific dusts and fumes 4. Pneumoconiosis Silica-containing dusts 5. Noise-induced Hearing Loss Sound levels above 80 dB(A)1 ((effect*[tw] OR control[tw] OR controls*[tw] OR controla*[tw] OR controle*[tw] OR controli*[tw] ORcontroll*[tw] OR evaluation*[tw] OR program*[tw] OR prevention*[tw] OR protect*[tw]) AND (work[tw]OR works*[tw] OR work*[tw] OR worka*[tw] OR worke*[tw] OR workg*[tw] OR worki*[tw] ORworkl*[tw] OR workp*[tw] OR occupation*[tw]) NOT animals[mh])2 (meta-analysis[mh] OR meta-analysis[pt] OR meta-analysis[tiab] OR review[pt] OR review[tiab]) NOT(letter[pt] OR editorial[pt] OR comment[pt]) NOT ((animals[Mesh:noexp]) NOT (humans[Mesh])) 6
  7. 7. 6. Back Pain Ergonomic risk factors: manual material handling, bending and twisting, heavy physical load, static work posture, repetitive movements, whole-body vibration, stress-related risk factors 7. Injury Prevention Hazardous situations at workTable 1 Overview of risk factors to be addressed by essential occupational health interventionsWork-related cancer and its related exposureFor work-related cancer, there are two major cancer types that are associated with the exposures at work.Cancer of the trachea, bronchus or lung is associated with inhalatory exposure to arsenic, asbestos,beryllium, cadmium, chromium, diesel exhaust, nickel and silica and radon. Leukaemia is associated withexposure to benzene, ionizing radiation and ethelyne oxide. Except for arsenic and nickel the effects of allthese agents come through inhalation. Arsenics route of exposure is through ingestion and for nickel it canbe both ingestion and skin absorption.6Exposure to these agents in low and middle income countries is not self-evident. Beryllium is only used in asmall and specific industry. The same holds for benzene, ionizing radiation and ethelyne oxide which aremainly used in chemical and other industries and in small amounts in health care. These compounds are thusoutside the scope of this study.Arsenic is an important component of pesticides and herbicides and used in timber treatment and pigments.However, exposure mainly occurs during the manufacturing of these products. It is therefore not expectedthat this exposure will be very prevalent among our target group and thus it falls outside the scope of thisstudy. Arsenic occurs also naturally in the soil and leads to arsenic contaminated ground water. A mainsource of exposure to arsenic is through the use of contaminated ground water for cooking. There are severalsolutions to prevent uptake of arsenic from contaminated groundwater but this is outside the scope of thisoccupational health study.Both cadmium and nickel are ingredients of batteries that have a ubiquitous presence but this does not lead tooccupational exposure of our target population. Cadmium, chromium and nickel are present in weldingfumes. Welding is a ubiquitous activity that is very prevalent in all parts of the world. Therefore I includedinterventions for reducing the risk of inhaling welding fumes.Exposure to diesel exhaust is prevalent around the world but it is only to a limited extent occupational.Occupational exposure mainly occurs in traffic controllers, railroad workers and truck/car drivers which areoutside the scope of this study.Asbestos and silica are widely spread around the world and lead to health problems through inhalation. Bothsubstances lead also to pneumoconiosis. Exposure to asbestos occurs in the asbestos mining, ship building 7
  8. 8. and construction industry. The latter seems most relevant for our study. The same holds for silica, to whichworkers are exposed during mining of coal and in the construction industry during all kinds of activities thatinvolve cutting, drilling or blasting of stone that contains silica. These activities occur frequently throughoutthe world and should be the focus of preventive activities and are thus included.After considering the prevalence of exposure in LMI-countries, I further elaborated preventive activities tolower exposure to asbestos, silica and welding fumes because these are the main exposures that cause work-related cancer.Virtually all exposure to asbestos, silica and welding fumes occurs through inhalation. Preventive effortsshould thus focus on prevention of inhalation of these substances. Technically, there are two approaches toprevent inhalation: source-oriented and exposure-oriented. Source-oriented solutions are directed at changingthe source in the production process by substituting for example asbestos with another material so that nofibres will be released anymore. Exposure-oriented solutions focus on taking away the exposure withoutactually eliminating or reducing the source. Examples of exposure-oriented solution are local exhaustventilation, personal protective equipment or dust control measures. Especially exposure to asbestos andsilica occurs as a dust in which tiny solid particles are carried by air currents and are capable of remaining insuspension for a period of time. In a technical sense, dust control is well studied and there is a wealth ofinformation on control measures both source-oriented and exposure-oriented.7Pneumoconiosis and related exposuresPneumoconiosis is the term used for all dust damage done to the alveolar part of the lung including the partsof the lung that do not have a mucociliary lining, but it does not include bronchitis, asthma or cancers byconvention.6 Pneumoconiosis can thus be caused by a number of inorganic dusts the toxicity of whichdepends on particle size, shape and chemical composition of the dust. The most toxic are asbestos fibres andsilica dust. The most commonly occurring is coal dust. Ultimately the disease leads to fibrosis andemphysema of the lung. There is no cure and the only way to prevent the disease is to lower dust levels oreliminate exposure totally. Exposure to asbestos, silica and coal dust is a relevant exposure for low andmiddle income countries.The cause of pneumoconiosis is inhaled dust and therefore dust control and prevention of inhalation are alsohere the hallmark of prevention.Chronic Obstructive Pulmonary Disease and related exposuresChronic obstructive pulmonary disease (COPD), defined as non-reversible chronic airflow limitations, isrelated to dust exposure which is a comparable route of exposure as in pneumoconiosis or occupationalasthma. 8
  9. 9. Primary prevention thus uses the same pathways and I will not further elaborate the prevention of COPDonly. I assume that by preventing pneumoconiosis and occupational asthma also COPD will be prevented.Occupational Asthma and related exposuresAlso the primary prevention of occupational asthma is based on the prevention of inhalation of substancesknown to cause asthma. These can be divided into high molecular weight substances, usually organic dustssuch as grain and wood dusts, and low molecular weight substances such as diisocyanates, metals andwelding fumes.Primary prevention of occupational asthma is thus similar to primary prevention of inhalation exposure andwill require the same means as for other inhalation exposure.8Noise induced hearing loss and related noise exposureNoise induced hearing loss is caused by long term exposure to noise at levels greater than 80 dB(A). ThedB(A) stands for decibels for which the sound level has been corrected according to the hearing abilities ofthe human ear. Once hearing ability has been lost, there are no means to recover the lost capacity.Therefore, decreasing exposure to noise levels greater than 80 dB(A) is the only means of prevention fornoise induced hearing loss.However, it is clear that not every worker is equally sensitive to the damaging effects of noise. Even afterforty years of exposure to 100 dB(A) a substantial proportion of workers will still have normal hearing fortheir age.9 Given these differences in sensitivity, early detection of workers who are most susceptibility tonoise and focussing our preventive efforts on these workers would be worthwhile. Currently, such a test ishowever not available and we are not able to accurately predict who will sustain the greatest hearing loss.10This leaves us with exposure reduction as the main means of prevention. Along the same lines as withinhalation exposure prevention, there are two general approaches for exposure reduction: technicalengineering controls and hearing protection. I will look for evidence for these two approaches.Back Pain and related biomechanical exposureFor back pain, there is no clear cut physical model that explains how exposure at work causes back paincomparable to exposure to silica dust and silicosis. This makes the primary prevention of back pain morecomplicated than inhalation exposure prevention. The cardinal symptom of back pain is subjective and hasvarious dimensions that are difficult to measure. Even though attempts to standardise approaches tomeasuring back pain have been undertaken, reporting of back pain as an outcome still varies widely acrossstudies 11. In general, two different models of occupational back pain causation are in use. One model is thatback pain occurs because biomechanical overload during a considerable time period has led to osteoarthritis 9
  10. 10. of the vertebrae and the intervertebral discs in the lumbar spine. These anatomical and physiologicalchanges, in turn, lead to pain sensation. Psychosocial stress is thought of as an intermediary factor in thisprocess. Stress can either lead to different positions leading to greater wear and tear of the lumbar spine or itcan lead to an increased pain sensation. Another model used mainly in the North American workerscompensation insurance context is the idea of a back injury that results from biomechanical overload atwork. The idea of an injury implies that there is an immediate connection between the overload and theresulting pain. Thus, only back pain that occurs in immediate connection to the biomechanical overload isrecognised as occupational back pain. For our search for relevant exposures, both models would lead to thesame inference that exposure to biomechanical overload of the lumbar spine is the main cause of back pain.Primary preventive interventions should therefore lead to a decrease of biomechanical exposure.Even though back pain as such is an unpleasant experience, more importantly back pain leads to incapacityfor work with resulting increase in sick leave and long term occupational disability. Because this is a majorproblem both for the afflicted individual and society at large, many preventive efforts thus focus onpreventing disability. More psychosocial factors, both at individual, company and society level, influence thepathway from back pain to back disability. The primary cause will still be the origin of back pain andprimary prevention would still aim at taking away these causes.Biomechanical overload of the lumbar spine is defined as a load that exceeds the tolerability of the structuresof the spine. There is no consensus on how to calculate this 12. Nevertheless, consensus exits on activitiesthat increase the load on the spine and that should be minimised. These activities are manual materialhandling such as lifting, frequent bending and twisting of the lumbar spine and exposure to whole-bodyvibration 13.Biomechanical overload seems a very common exposure in LMIC where work is less mechanised andsophisticated manual material handling aids are less available. Therefore, I searched for evidence ofeffectiveness of interventions that can decrease biomechanical exposure at work especially through lifting,bending and twisting and whole-body vibration.Injuries and related exposure to hazardous situationsThe etiology of injuries is more complicated than that of occupational diseases and research has long beenhampered by a lack of a conceptual framework. Even though it is not always easy to discern injuries fromillnesses, I will define injuries as sudden-onset occupational injuries where energy exchange producesimmediately discernable tissue damage 14.In the public health arena, Haddon was one of the first to model the etiology of injuries. He argued that aninjury results from the interaction between a host, an agent and the environment. In this model the host is theperson who receives the energy and the agent is the vector that transfers the energy. In addition, Haddon 10
  11. 11. conceptualised three temporal phases that determine the likelihood of injury. First, there is the pre-eventphase that includes the activities and the conditions of the host, the agent and the environment. Then there isthe event during which the energy is transferred to the host. In the post-event phase first-aid and medical carecan still add to survival and recovery. Together the temporal and energy dimensions make up the so-calledHaddon matrix that can be used as an analytical tool for injury prevention. Preventive approaches are furtherdivided into active and passive approaches in which the passive approach is, counter-intuitively, consideredthe most effective. An active approach means that a person has to actively take countermeasures to avoidinjury whereas the passive approach does not require human interaction 15-18.Another approach comes from psychology where the orientation has been on behavioural theories to explainoccupational injuries. Based on a meta-analysis of personal and environmental risk factors for injuries andaccidents, Christian and Wallace (2009) put forward a conceptual model of workplace safety.19 In themodel, situation-related factors such as safety climate and leadership interact with person-related factorssuch as personality characteristics, job attitudes and safety knowledge and motivation. Together, thesituational and personal factors shape safety performance such as safety compliance and safety participationwhich ultimately leads to the prevention of injuries.Some sectors are notoriously more dangerous than others. For example agriculture and construction industryare among the sectors with the highest injury rates 20;21. In addition, certain groups of workers sustain moreinjuries such as immigrant workers.22It seems, that the conceptual model of injury etiology fits well with the approach of primary prevention that Ihave taken in this report. I looked for evidence of effectiveness of environmental and behaviouralinterventions that address hazardous situations in the pre-event phase.From exposure to preventive interventionsFor exposure reduction, the general approach is, similar to other risk reduction strategies, a three stepapproach in which risks first have to be identified, then evaluated and finally controlled or managed. For themanagement of especially chemical health hazards this approach has been best developed but the strategy isapplicable to all kinds of risk problems.In practice many approaches have been developed to facilitate risk reduction. For example hazardidentification checklists have been developed that list potential risks in specific businesses. Such check listsenable workers or occupational health professionals to immediately focus on problems at hand in theirspecific business.23Especially the evaluation of chemical risks is greatly facilitated by the lists of Occupational Exposure Limits(OEL). An OEL list states for a number of chemicals what the level of exposure is below which there is no 11
  12. 12. appreciable health risk. Most of these lists are available through the Internet nowadays.24 In practice, thismeans that one measures the exposure in a specific workplace and compares this with the appropriate OEL.If the exposure is below the OEL, no control measures are needed.However, this approach, of first measuring risks and than evaluating, has been criticised especially for smallbusinesses because it focuses very much on measurement strategies. Measurement of chemicals oftenrequires specific professional expertise and financial resources that is not available in small businesses andthus, valuable resources are spent on activities that do not necessary lead to risk control. Therefore,Ellenbecker argued that risk control strategies in small businesses much better immediately focus onengineering controls than on measuring and evaluating.25Engineering controls or interventions are part of the so-called hierarchy of controls. The meaning of thishierarchy is that is postulated that some control measures should always take priority over other controlmeasures because they are valued higher. Basically, this theoretical approach lists two approaches ofexposure reduction: engineering controls and administrative controls. Engineering or technical controlscomprise exposure reduction through substitution of the hazardous agent or process changes that eliminateexposure and isolation or ventilation of the source of exposure. Administrative controls comprise personalprotective equipment, worker education and training and scheduling work such that the duration of exposureis reduced. Because engineering controls solve exposure problems in a more fundamental way, they arealways to be preferred over the administrative controls. For example, substitution of the source should bepreferred over the other solutions that are supposed to solve exposure problems less well. Since this is atheoretical approach it is unclear how this works out in practice.Applying engineering controls without an intermediate step of carefully evaluating the exposure levels isalso in line with the idea that many exposures do not really have a level below which there are no healtheffects. Even though there are OELs for ionizing radiation, the strategy here is to get the exposure As LowAs Reasonably Achievable (ALARA) because there is no real threshold for an effect on health and with eachincrease in exposure there is a concurrent increase in risk to a worker. The OEL is based on what isconsidered an acceptable risk compared to other activities in life but this does not guarantee absoluteprotection.26Another related concept that has been developed in the control of hazardous chemical exposures at work inthe past decade is the so-called control-banding.27 "The concept is to put chemicals (and other substances andprocesses) into one of a number of “bands” depending on its hazard. The risk is a combination of theinherent toxicity of the substance and the likely exposure. The exposure is assessed qualitatively bydetermining the form in which the chemical exists (particle size, gas, vapour), the quantity used, and theprocesses in which it is used. The approach recommends control strategies to be chosen prior to and possiblyin lieu of exposure measurements taken in the workplace. Control banding may be useful in situations where 12
  13. 13. there are no OELs and/or when quantitative exposure assessments would be difficult to obtain (e.g., smallindustries that lack the technical expertise or in developing nations)." 28Thus, it follows that for primary prevention of occupational diseases and injuries, specifically environmentalinterventions should be the primary choice. If these are not available, behavioural or clinical interventionscan be used such as education and training or health examinations.In terms of environmental interventions, it is important to make a distinction between interventions that aretechnically possible and that work under laboratory conditions and the effect of these interventions underfield conditions. Dust control measures, for example, are effective provided that they are carried outappropriately. However, the implementation of these technical measures in work places is an entirelydifferent matter. How can we make an employer or a worker take measures and change their workingroutines so that no dust will be stirred up? For an effective occupational health intervention, we need acontrol measure that is technically working but as such this is not sufficient. In addition, we also needinterventions that convince employers and workers to change their behaviour and implement the technicalcontrol measures. Niewöhner and Cox have nicely illustrated this in what they call the Mental ModelsApproach 29;30. They showed that it is highly unlikely that safety information as provided by Material SafetyData Sheets will be understood and used by managers and workers in its current technical format. Ifinformation is taken up and acted upon, depends on the mental model that managers and workers have of thehealth hazards at work and the possibilities of their control. It is therefore important to take their beliefs andtheir concepts of a safe workplace into account. Thus interventions become less technical and much morebehavioural.Most engineering measures are evaluated in uncontrolled before-after experiments over a short-time period.For example technical changes on machinery to make it less noisy can be implemented. A noisemeasurement before the implementation and after the implementation would convince most of us of theeffectiveness of the technical measures. In such a technical case study, it is usually clear that the technicalimprovements are the only factors that have changed over the relatively short time period of follow-up suchas hours or days. These studies usually do convince that technical measures are feasible and do lead to lowerexposure. However, experiments intended to demonstrate that the measures can be implemented need to bewell-controlled and need a longer follow-up time to be convincing. In addition to the intervention, there arealways many other factors that can lead to workplace changes in companies that can easily confound theeffects of an intervention. Interventions will attract the most motivated firms to participate in the researchproject and thus the results of an experiment can be easily distorted as a result of this selection bias. Thereare only very few well randomised experiments of exposure reduction available and the results have beendisappointing probably because the behavioural change component of the intervention has beenunderestimated.31 Also in less well-controlled implementation projects, researchers report that the results ofworkplace changes are only modest.32 As part of this report, I especially looked at evidence of the 13
  14. 14. effectiveness of implementation of technical measures that reduce the exposure to occupational carcinogensin workplaces.Pre-employment examinations can also be considered as primary preventive interventions as their objectiveis to prevent that susceptible workers will be exposed. Thus this can also be called an exposure preventionintervention. It is important to take into consideration that the benefits of pre-employment examinationsusually are not realised without the draw-back of denying employment to the prospective employee.There is a recent systematic review of the effect of pre-employment health examinations that lists allcontrolled studies that have been performed.33 I will not search for the effect of pre-employment healthexamination for each exposure but I will use the results of this review.3. Evidence of effectiveness of occupational health interventions3.1 Interventions for decreasing inhalation exposure Environmental interventions: substitutionRoelofs et al performed a systematic search of the occupational hygiene literature to locate articlesdescribing, what they call, control or prevention strategies for chemical hazards in actual workplaces.34 Theywere disappointed to find, among the located 92 articles, only two that explicitly discussed the hierarchy ofcontrols and only four that actually compared different control strategies. They concluded that “despite theirtheoretical primacy, primary prevention strategies—those focusing on reduction of hazards at the source—are not commonly considered in practice; they ranked third in frequency of citation in the literature. Andalthough industrial hygienists sometimes do consider these strategies, they are not often implemented. Only11% of the articles described the actual implementation of primary prevention strategies.In line with their findings I could locate only one systematic review that provided evidence of effectivenessof substitution as an intervention to decrease inhalation exposure. The effect of substitution on the veryspecific exposure to latex was studied in one systematic review. The authors included eight studies ofvarying methodological quality. They concluded that there is adequate evidence that substitution ofpowdered latex gloves with low protein powder-free natural rubber latex gloves or latex-free gloves leads toa reduction of occupational asthma.35 Cullinan et al, in a review of asthma prevention, argue that there fewexamples of the evaluation of primary prevention of asthma but those that are described as case studiesprovide evidence that this is a feasible and highly effective strategy. Examples of primary prevention are thechange from the use of powder to granulated proteases in the detergent powder industry, laboratory animalallergy and also latex allergy measures in health care.8 14
  15. 15. Environmental interventions: other control measuresThe effectiveness of control measures for inhalation exposure has been studied in the occupational hygieneliterature in various ways. Researchers have tried to show the effectiveness of control measures as a genericapproach. Some researchers have tried to summarize the effectiveness of what they called -risk managementmeasures- based on studies that compared the exposure with and without control measures.36 Othersprovided an overview of measures to control dusts especially.7 Then, there are researchers that reviewedstudies that reported trends in exposure over time and tried to relate these trends to specific interventions.37-40However, none of them used formal systematic review techniques or techniques for meta-analysis and it istherefore difficult to judge the value of these reviews. They neither make a distinction between studies thatmeasure the technical outcome versus studies that have evaluated the implementation of these technicalmeasures in companies. The results of these studies are summarised underneath.Fransman et al provide an overview of the efficacy of seven broad but well defined categories of controlmeasures for inhalation exposure excluding substitution. They calculated with what percentage the exposurecould be reduced by various control measures: 36 - enclosure (50%, 95% Confidence Interval 4% to 74%) o complete or partial encapsulation or encasing of the source such as lids or screens - local exhaust ventilation (82%, 95% CI 78% to 84%) o any kind of exhaust ventilation system close to the source with or without enclosure - specialized ventilation systems (87%, 95% CI 73% to 94%) o mechanical ventilation systems specifically designed to displace air in small designated areas such as a walk-in booth or clean zone - general ventilation (43%, 95% CI 17% to 61%) o natural or mechanical ventilation of whole work areas such as opening windows or doors - suppression techniques (83%, 95% CI 77% to 88%) o the addition of an additive to an activity or process to suppress emissions such as water or oil - segregation of sources (no studies) o total isolation of source from the work environment such as in a special room - separation of the worker (87% 95% CI 71% to 94%) o worker is in a personal enclosure within the work environmentThey included any kind of study that compared the exposure with and without the control measure. Thiscould be a cross-sectional study, a laboratory experiment or a field study to evaluate the implementation.Efficacy was calculated as the percentage reduction of an exposure: exposure without controls minusexposure with controls divided by exposure without controls times 100. For example the exposure withoutcontrols is 10 mg/m3 and with controls it is 1 mg/m3. This results in a efficacy value of 90%. The resultswere averaged over the various control measures to give an indication of the overall efficacy per categoryand adjusted for study design, sampling strategy and measurement type. 15
  16. 16. In total they included 433 comparisons derived from 90 articles. Most comparisons (N=177) were derivedfrom intervention field studies and from local exhaust ventilation (N=280). The average efficacy values aregiven in the table with the categories above. The results indicate that most control measures are highlyeffective in reducing exposure between 80% and 90% except for enclosure and general ventilation thatreduce the exposure to a lesser degree of between 40% and 50%. The authors did not find a difference fordusts, fumes, vapours or mists in the efficacy of the control measures.For practical reasons the authors did not include studies on measures that changed work processes such assubstitution and neither had they included studies on respiratory protection. The authors acknowledge thatthe preferred study design to evaluate the effectiveness of the control measures would be an interventionstudy aimed at evaluating the implementation of the control measures. Thus the included studies can onlyprovide limited evidence of effectiveness. In addition, it is easily conceivable that there will be considerablepublication bias with studies of this type. Because many of the included studies are actually case studies,authors would be reluctant to publish studies that do not show a decrease in exposure. A review of publishedstudies will thus mainly include studies with positive effects.Creely et al summarized what they called trends in inhalation exposure with the aim to summarise factorsthat may have been responsible for the observed changes.39 To be included papers had to describe inhalationexposure over some time span but the authors did not specify the length of the time span. From all papers theauthors extracted or calculated the percentage decrease in exposure per year. The results were reportedaccording to exposures to aerosols, gases and vapours and fibers. The suggestions on the causes of thechanges by the authors of the primary papers were also reported. The results were summarised in a narrativeway and no attempt to meta-analysis was made. They included 25 papers that reported on exposure trendsand these papers included 87 separate exposure trends. One paper that reported on exposures in the Americanpulp and paper industry over the time period between 1979 and 1994 contributed 36 exposures trends.41 Ofthe 87 reported exposure trends, 61 were measured in the US. The authors summarise the evidence availablein these 87 trends as in the majority of instances there were significant reductions in exposure. Across studiesthe average yearly decrease in exposure was - 7% ± 5% for aerosols (N=38), - 8% ± 7% for gases andvapours (N=39) and - 15% ± 11% for fibres (N=10). From another not totally overlapping 21 papers theauthors summarised the reasons for decline or increase of exposure. Regulatory changes were mentionedmost often as the reason for decline of exposure. Other reasons were implementation of occupational healthprogrammes, changes in production equipment or methods and installation of control measures such asventilation or elimination or substitution of the source. It was not possible to make any general conclusionsabout the causes of the decline.A third paper reviewed the trends in exposure to metal working fluids. Even though this exposure is outsidethe scope of this study, it provides better evidence of trends in exposure over time. The review included 48papers on fluid aerosol measurements of metalworking-fluids over a time period ranging from 1949 to 2007.The arithmetic mean exposure was averaged over ten year periods for 155 measurement situations with the 16
  17. 17. following result: prior to 1970 5.4 mg/m3, 1970-1980 2.5 mg/m3, 1980-1990 1.2 mg/m3, 1990-2000 0.5mg/m3 and in 2000-2007 0.5 mg/m3. These figures show a ten-fold decrease or 90% decline in exposureover time. These reductions in exposure are thought to be brought about by installation of aircleaners, partialenclosure of machines and local exhaust ventilation based on better awareness of the toxicity ofmetalworking fluids.40Symanski et al also systematically reviewed exposure decline over time but did not include any reference tothe possible interventions that could have induced these declines.42 Their conclusions are in line with theother reviews. Based on 119 published studies they calculated a yearly decline in exposure of 15% forwestern Europe, of 17% for North Amerina, of 60% for Eastern Europe, of 47% for Japan but only 5% forother countries.I conclude that there is low quality evidence from four systematic reviews of low quality that controlmeasures to reduce inhalation exposure are effective. General ventilation and enclosure seem to be lesseffective than other measures. Apparently through enforcement of regulation and implementation oftechnical controls a general decrease in inhalation exposure has occurred in the US and other industrialisedcountries in the past 30 years.On a more technical level dust control as a form of specific inhalation exposure prevention has beenreviewed by Smandych as a generic measure to reduce exposure to dust.7 She reviewed dust controlmeasures both from the point of view of the dust sources and from the point of view of controlling dust ingeneral. Dust sources in the production process are usually related to storing, processing, packaging, feedingor hauling. Enclosure of most of these processes is a feasible option. For general control strategies there aredust collection systems such as local exhaust ventilation and dust suppression systems such as wet or oilysprays. The authors conclude that most of the information is merely rule-of-thumb or general guidelines andthat more research is needed to provide a more consistent and systematic approach. A test of dustiness ofmaterials handled at workplaces has been developed that will help in evaluating the dustiness of material tobe used at work.43 This will help in selecting materials that are less dusty.In addition, a wealth of studies have been published that reviewed techniques to reduce specific inhalationexposure such as due to abrasive blasting, mortar removal, hand tools for concrete cutting, masonry cuttingand tuckpointing44-47 I will not review all these specific techniques as this is beyond the scope of this study.These studies show that technical measures to control inhalation exposure are well known and well studied.There were no systematic reviews of exposure reduction in welding. I found two studies that showed thatlocal exhaust ventilation can substantially reduce exposure to chromium and manganese in weldingprocesses applied in the construction industry.48;49 17
  18. 18. Environmental measures: regulation and other incentivesTorén and Sterner discussed that different regulatory strategies can lead to similar results in exposurereduction.50 They provide some evidence from case studies in various countries that taxes, subsidies andbanning can lead to similar reduction of exposure to trichloroethylene. Elsner et al reviewed case studies ofeconomic incentives in various European countries and concluded that they can be an effective strategy forimproving occupational health.51 An example of successful regulation of prevention of inhalation exposure isthe case of asbestos. The use of asbestos in production processes has been successfully banned from mostindustrialized countries where exposure to asbestos nowadays mainly occurs in construction workers duringdemolition and renovation of buildings. Recently, the Collegium Ramazzini group has renewed their call fora universal ban on the mining and use of all forms of asbestos.52 One of the main arguments for a ban is thatit is impossible to control the use of asbestos to ensure that no health hazards will occur.53Even though good systematic reviews are missing in this area, it seems that regulation and economicincentives can both lead to substantial reduction of exposure. Behavioural: respiratory protection for preventing inhalation exposureFor respiratory protection, the same holds as for technical control measures in general. The effectiveness ofrespiratory protection is the result of the interaction of proper design and manufacturing (properfunctioning) and actual fit, maintenance and cleaning and proper use by the wearer in workplace practice(proper use) as Brouwer et al put it.54 Thus, results of laboratory testing and technical features of the devicesnever hold under practical circumstances. The protection factor of respiratory protection has been shown todecrease with a factor 450 between simulated and real workplace testing.55 In addition, it is clear that withoutproper instruction and training in its use, the exposure reduction will be even worse.56 Practical featuresmake the use of respiratory protection difficult. If the wearer has a beard, the protective properties ofrespiratory protection will be lost.55 Brouwer et al propose that for personal protective equipment that hasbeen shown to be functioning properly additional criteria for its proper use should be adopted. These criteriaare: awareness of the need to use the personal protective equipment, instruction and training, ability toperform work tasks with the protective equipment and acceptability based on discomfort rating.54There are no systematic reviews that have looked at the effectiveness of respiratory protection under fieldcircumstances. In none of the reviews of exposure trends over time the effects of respiratory protection havebeen taken into account. Given all the practical constraints for proper use, it seems unlikely that respiratoryprotection can be an effective measure of control of inhalation exposure in low and middle income countries. Clinical: pre-employment examinations and drugsThe effectiveness of pre-employment examinations has been debated for a long time.57 Most authors haveargued against the effectiveness of pre-employment examinations for the following reasons. Pre-employmenttesting is basically a form of screening by which prospective job applicants are tested for personal risk 18
  19. 19. factors that make them more vulnerable to the exposure of the prospective job. For those who test positive anintervention should be applied to eliminate the risk. Most research has focussed on the tests that are appliedin pre-employment examinations. Authors have argued that the tests are not specific enough and label manyjob applicants as being at risk while in reality they are not. In epidemiological terms, the tests yield too manyfalse positives. Denying the job to the worker who tests positive is the most frequently applied intervention.This means that those who are false positive are wrongfully denied access to work. Based on modellingstudies, authors have argued that the costs of wrongfully denying work to those who are false positives faroutweighs the benefits of preventing occupational diseases in those who are correctly classified as being atrisk.58-60 However, there are no studies that have conducted a proper economic evaluation. There are also nostudies that have followed the job applicants after they were rejected based on the pre-employmentexaminations.Evaluating the effectiveness of screening procedures is complicated because the outcome depends both onthe quality of the diagnostic tests involved and the effectiveness of the intervention. Screening can beevaluated by comparing the whole screening procedure including the interventions to a control conditionwithout the procedure. An alternative evaluation procedure is to study the effectiveness of the interventionsonly in candidates who screen positive as the interventions effectiveness is the most important part of theprocedure. There are basically three different interventions that can be applied to job applicants that have arisk factor: they can be denied the job they are applying for, the prospective workplace can beaccommodated to their risks or the job applicant can be trained so that they are no longer at risk.There is only one Cochrane systematic review that has looked at controlled studies that have evaluated theeffectiveness of pre-employment examinations.33 In this review, nine studies were included. Seven evaluatedintroduction of pre-employment examinations versus no pre-employment examinations. One of these sevenstudies was about the prevention of occupational asthma. Incorporating a bronchial challenge test forworkers in the aluminium industry decreased the number of cases of occupational asthma over time in aninterrupted time series compared to the time period when pre-employment examinations were used withoutthese tests.Prevention of work-related cancer can theoretically also be achieved through vitamins such as beta-carotene,which could be prescribed for people at risk. There is also a Cochrane Review that concludes that there iscurrently no evidence to support recommending vitamins such as alpha-tocopherol, beta-carotene or retinol,alone or in combination, to prevent lung cancer. On the contrary, a harmful effect was found for beta-carotene with retinol at pharmacological doses in people with risk factors for lung cancer (smoking and/oroccupational exposure to asbestos).613.2 Interventions for decreasing exposure to noise 19
  20. 20. Environmental interventionsI found one systematic review of interventions to reduce exposure to noise.62 The authors found evaluationsof the effects of the following interventions:- the effect of the introduction of legislation on noise levels (1 study)- the long term effect of hearing loss prevention programmes in companies on hearing loss (14 studies)- the short term effect of hearing protection on temporary hearing loss or noise exposure (6 studies)The one study that examined the effect of new legislation in reducing noise exposure measured the impactduring 18 consecutive years in the mining industry in the US, either side of the implementation of legislation.It found that the median noise level decreased by 28 decibels immediately after the introduction oflegislation.The effectiveness of the hearing loss prevention programmes in companies was evaluated by comparinghearing loss in workers that were exposed to noise but who were protected through a hearing-loss preventionprogramme with the natural hearing loss in workers that were not exposed to noise. The studies producedmixed findings and, in some, workers who were protected from noise still had three to four times the risk ofhearing impairment compared to similar people not exposed to noise in the first place. In threeimplementation studies, better quality hearing loss prevention programmes were shown to have asignificantly lower risk of hearing loss than lower quality programmes. Most of the hearing loss preventionprogrammes were from the US or older studies that consisted mainly of instruction to workers to wearhearing protection, even though some studies also included engineering controls.The studies on the short-term effects of hearing protectors showed that these can reduce noise levelssufficiently. An important factor is that the hearing protectors have to be worn properly. For example,workers need instruction for the insertion of hearing plugs to make these sufficiently protective.The authors concluded that there is low quality evidence that legislation can reduce noise levels inworkplaces but contradictory evidence that prevention programmes are effective in the long-term. Eventhough case studies show that substantial noise reductions can be achieved, there is no evidence that this isrealised in practice. It is concluded that better implementation and reinforcement of legislation and hearingloss prevention programmes is needed if people’s hearing is to be better protected. Behavioural interventions: promotion of hearing protectionIn addition to this review, there is one other Cochrane systematic review on interventions to enhance the useof hearing protection.63 In this review, three studies were included that reported on the primary outcomemeasure that was the proportion of participants wearing hearing protection. One study was a clusterrandomised trial of 17 schools for vocational training in farm work with 3 years follow-up. The participantsat the intervention schools (N=375) received a hearing test and an extensive educational interventionwhereas the participants at the control schools (N=378) received only a hearing test. The percentage of pupils 20
  21. 21. that reported wearing hearing protection at least sometimes increased from 23% to 83% at the end offollow-up whereas these figures for the control group were 24% and 35% respectively. Another study amongautomotive workers (N= 1325) exposed to on average 90 dB(A) evaluated the effect of a computergenerated message that was tailored according to the amount of hearing loss and to the individual predictorsof the likelihood of wearing hearing protection. This tailored message was compared to general informationand to a control condition where workers saw a commercial video on hearing loss prevention. In a follow-upof the same study the workers were again randomised to receive a booster message sent to their privateaddresses after one and three months after the first message. In the third study, the same tailored interventionwas evaluated in a different population. The tailored message resulted in an increase of 6% of the self-reported amount of time that hearing protection was worn in both studies compared to either the non-tailoredintervention or the control condition. The other studies in the review did not report on the primary outcome.The authors conclude that there is evidence from one study that school-based interventions can be effectiveand that messages tailored to the needs of the individual can be more effective than general messages. Clinical interventionsAs mentioned before, there are no reliable tests to detect those that are sensitive to noise that could be used ina pre-employment examination. Neither did I find studies that used pre-employment examinations as anintervention to reduce noise-induced hearing loss.Even though magnesium has been used as a drug to prevent hearing loss among those exposed to noise, thereare no systematic studies that have reviewed its effectiveness.A conclusion similar to that on prevention of inhalation exposure applies to reduction of noise exposure.Technical solutions for decreasing noise levels are feasible, tested and available. There is low qualityevidence from a high quality review that legislation can help implementing these interventions, which leadsto lower noise levels. There is contradictory evidence that noise-induced hearing loss decreases as a result ofhearing loss prevention programmes. Hearing protection can adequately reduce exposure but needseducational or behavioural interventions to be properly implemented to levels that protect workersadequately. There is low quality evidence that educational programmes at school or messages tailored to theneeds of the individual can increase implementation but it is unclear if this leads to sufficient protection.3.3 Interventions for decreasing biomechanical exposureControl of biomechanical exposure can be either directed at worker behaviour such as better liftingtechniques or at the workplace such as decreasing the loads to be lifted or improving the position in whichthe work has to be done. It is surprising how few studies have been conducted in this area. 21
  22. 22. Environmental interventions: load reduction and ergonomicsWith biomechanical exposure it is not always easy to make a distinction between environmental andbehavioural interventions. Ergonomic interventions usually require some kind of human participation but itis possible to reduce exposure without human interference for example by reducing the weight that has to belifted. In that sense, the American National Institute of OSH (NIOSH) has presented a valuable exposurelimit as a means to try to reduce spinal load at work. This consists of a relatively simple assessment tool thatcan be used to assess a recommended weight limit. The maximum recommended weight limit is 23 kg. Thelifting conditions, such as distance of the load to the body and the degree of trunk rotation have to bespecified and entered into a formula which returns a recommended weight limit for these conditions.64 Eventhough this is a practical approach that in theory should be able to reduce spinal load, there are no controlledstudies that have evaluated if using such an exposure limit prevents back pain.The effectiveness of participatory ergonomic interventions on health outcomes has been reviewed by Riviliset al 65 earlier published as Cole 2005. The implementation of this type of interventions thus requires activeparticipation of workers. This review included seven studies that evaluated the effect of ergonomicinterventions on musculoskeletal disorder symptoms. Three of these were RCTs. The highest quality studyshowed similar symptom levels in the intervention group as in the control group after 10 months follow-up.The other two studies found little change. Of the non-randomised studies, two found a positive result and twofound a non-significant result for back symptoms. Even though the authors conclude that this is moderateevidence that participatory interventions have a positive impact on musculoskeletal disorder symptoms, thereview does not provide evidence that back pain can be prevented by ergonomic interventions.A more recent review of ergonomic interventions (physical and organisational) to prevent back pain inworkers included 10 RCTs. There was low to moderate quality evidence that physical and organisationalergonomic interventions were not more effective than no ergonomic intervention on short and long term backpain incidence/prevalence and short and long term back pain intensity.66 The same authors found a similarresult in a cluster randomised trial that they conducted as a result of their review.67 Behavioural interventions: education and trainingSince long it has been assumed that there is a correct lifting posture that decreases biomechanical load on thelumbar spine. There is however no consensus in the biomechanical literature what this correct lifting postureis.12 Based on these assumptions, there has been considerable effort invested in interventions to makeworkers change their lifting behaviour. These efforts have been especially concentrated in occupations suchas nursing in which it is difficult to change the load because this is inherent to the task of lifting patients. Inone older review on prevention of back pain in general, Van Poppel et al found 11 trials.68 There were sixRCTs that evaluated education but it was concluded that these contained no evidence of a preventive effectof education. 22
  23. 23. Since then, several reviews have addressed the effectiveness of manual material handling advice to preventback pain.69-72 They are mostly based on the same studies and all conclude that manual handling training islargely ineffective in reducing back pain or back injury.Verbeek et al recently updated the review of Martimo et al of advice and training for manual materialhandling to prevent back pain.73 The authors included in this updated review ten RCTs with 20.152employees and eight cohort studies with 1176 employees. All studies focused on prevention of back pain.Ten studies compared some kind of training to no intervention (4), a minor intervention (3), back belt use (1)or exercise (1) and one study compared training plus lifting aids to training only or no intervention. Theintensity of training ranged from a single educational session to very extensive personal biofeedback of theload on the lumbar spine. None of the included studies showed evidence of a preventive effect of training onback pain. Based on seven RCTs, there was moderate quality evidence that training resulted in similar backpain as no intervention with an odds ratio of 1.17 (95% Confidence IntervaI 0.68 to 2.02) and as minoradvice with an odds ratio of 0.93 (95% CI 0.69 to 1.25). The results of the cohort studies were similar tothose of the randomised studies. The authors conclude that there is moderate quality evidence that MMHadvice and training with or without assistive devices do not prevent back pain or back pain-related disabilitywhen compared to no intervention or alternative interventions. Clinical interventions: pre-employment examinationsThe same Cochrane review on pre-employment examinations as mentioned before included three studies thatused a functional capacity evaluation test in workers with high physical work load to preventmusculoskeletal injuries including back pain. The studies led to contradictory results with one study resultingin less musculoskeletal disorders and two studies that did not lead to a decrease. All studies led to an increasein rejected applicants. Moreover, if there are benefits, it remains to be seen if these outweigh the increase ofrejected job applicants.33 The very low quality of the evidence implies that future research could easilychange these conclusions.3.4 Interventions for prevention of injuriesA major problem in injury prevention research is that injuries are a relatively infrequent event in mostworkplaces. For evaluation research this means that studies are easily underpowered to find differencesbetween intervention and control group. Therefore one has to be cautious to not interpret this as interventionsnot being effective. Environmental interventionsThere were no studies that systematically looked at environmental interventions such as guarding to prevententanglement in machines or preventing falls from roofs. Hsiao and Simeonov reviewed the literature on fallprevention but they did so more from a theoretical point of view than as a review of prevention effectiveness 23
  24. 24. studies.74 Falls from roofs are one of the main causes of work-related fatalities in the construction industryand thus an important focus for prevention. Most measures for preventing falls focus on how to mitigate theresults once the fall is happening already such as using safety belts and guards. In line with the Haddon-matrix, the authors postulate that control of balance is the most important factor in the pre-event phase. Theyreviewed which factors can improve control of balance to prevent falls from roofs. They found evidence thatvisual and physical interaction with the environment, tasks such handling loads and personal factors such aswork experience and training are the main determinants of control of balance at heights. Visual interactioncan be improved for example by providing visual anchors or colour cues to improve depth perception.Physical interaction with the environment can be improved by extending the surfaces on which a workerstands, providing slide guards, increasing surface frictional properties, evenness and removing obstacles.Task related factors such as load handling, fatigue and task complexity can be improved to prevent falls fromroofs. Personal factors that can be improved were training and personal protective equipment. There were nointervention or evaluation studies that could support the suggestions for primary prevention of fall injuries.Tompa et al reviewed the effectiveness of prevention incentives used by insurance and in regulation.75 Iregarded this as implementation measures to get environmental interventions in place to prevent occupationalinjuries. He discerns two approaches to induce the desired preventive behaviour: experience ratings ofinsurance premiums and enforcement of occupational health regulation. Experience rating is the insurancepractice where premiums are reduced if you make fewer claims. They included all studies that evaluated oneof these interventions, were quantitative and had used a longitudinal design. Based on the quality and theoutcome of the studies they rated the available evidence as strong, moderate, limited, no or mixed.For experience rating they found moderate evidence that both the introduction of experience rating and thedegree of experience rating led to a decrease in injuries.There were only two studies that evaluated the introduction of occupational health regulation which led to aconclusion of mixed evidence for its effectiveness. Enforcement of occupational health regulation wasmeasured in various ways. Inspections were evaluated in 18 studies and the authors concluded that there waslimited evidence that inspections were associated with a reduction in injury frequency or severity. The 11studies that evaluated both the effect of inspections and the probability of a penalty showed mixed results.The other seven studies that evaluated the effect of an actual penalty showed strong evidence that thisresulted in a lowering of the injury rate. The authors warn for the possibility that regulation and experiencerating can give rise to so-called perverse incentives meaning that the incentive can also induce undesiredbehaviour such as not reporting injuries anymore to be able to receive a lower premium or to prevent apenalty.It has been shown that there is a strong relationship between safety climate in a company and the injury rate.Safety climate is defined as a specification of organisational climate that in turn is made up of sharedperceptions among employees concerning procedures, practices and kinds of behaviours that get rewardedand supported with regard to a specific strategic focus. When the strategic focus involves performance of 24
  25. 25. high risk operations, the resultant shared perceptions define safety climate.76 The topic has been extensivelyreviewed by Zohar but at the moment there is no empirical evidence on how to affect safety climate such thatit would help in reducing injuries. Prevention of injuries in agriculture and construction industryAnother approach to injury prevention evaluation is to look at a whole branch of industry. Branches ofindustry that are important to our topic are agriculture and construction industry.An older review on injury prevention in agriculture by de Roo et al concluded in 2000 that there was littleevidence that farm safety interventions were effective.77 Recently, this review has been updated in aCochrane Review.78 Five RCTs and three interrupted time-series (ITS) met the inclusion criteria. Five studiesevaluated educational interventions, one study financial incentives and two studies evaluated the effect ofregulation, one of regulating tractor roll-over protection structures and one banning of pesticides.Three RCTs with 4670 adult participants evaluated safety training and education. These studies did not findan effect on injury rates (Rate Ratio 1.02 (95% confidence interval 0.87 to 1.20)) Another two RCTs did notfind an effect of safety training among children.Financial incentives decreased the injury level immediately after the intervention in one ITS. Legislationrequiring rollover protective structures (ROPS) on new tractors was associated with a decrease in fatalinjuries but the same requirement for existing tractors showed no effect.Hartling et al performed a review of interventions to prevent specifically childhood farm injuries.79 Theyincluded 23 controlled studies of which four randomized. All interventions were educational in nature. Eventhough school-based programs and safety day camps appeared to be effective at increasing short-termknowledge acquisition, other interventions showed mixed results and no studies showed an actual reductionin injuries.79Another Cochrane Review gathered evidence on safety interventions in the construction industry.20 Here, theauthors found five interrupted time-series studies that met their inclusion criteria. Three studies evaluated theeffect of regulations, one evaluated a safety campaign, and one a drug-free workplace program on fatal ornon-fatal injuries compared to no drug-free workplace program. The overall methodological quality was low.The three studies that evaluated regulatory interventions did not show either an initial or sustained effect onfatal or non-fatal injuries, with effect sizes (ES) of 0.69 (95% confidence interval (CI) -1.70 to 3.09) and 0.28(95% CI 0.05 to 0.51).The safety campaign, which consisted of several methods aimed at preventing injuries, reduced non-fatalinjuries significantly both immediately (ES -1.82 (95% CI -2.90 to -0.75)) and in the long run (ES -1.30(95% CI -1.79 to -0.80)). Also the drug-free workplace program had an initial and sustained effect, reducingnon-fatal injuries compared to no intervention (ES -6.74 (95% CI -10.02 to -3.54) and -1.76 (95% CI -3.11 to-0.41)). 25
  26. 26. The authors concluded that the vast majority of technical, human factors and organisational interventionswhich are recommended by standard texts of safety, consultants and safety courses, have not been adequatelyevaluated. There is no evidence that regulations for reducing fatal and non-fatal injuries are effective. Thereis limited evidence that a multifaceted safety campaign and a multifaceted drug program can reduce non-fatalinjuries in the construction industry. Behavioural interventions: Occupational Safety TrainingEducation and training to increase knowledge and model safe behaviour have long been the mainstay ofinjury prevention. An extensive review of the literature from 1980 to 1996 by NIOSH in 1998 categorisedtraining as more narrow instruction whereas education was defined as broader instruction.80 The authors alsocategorised occupational health training and education into four different programme types with increasingassumed effectiveness: fundamental training aimed at instruction of proper work practices and use ofpersonal protective equipment, recognition programmes aiming at hazard recognition and control, problem-solving programmes and empowerment programmes that go beyond just problem-solving but use a totalquality management approach. They divided the literature further into training that aimed at reducing injury-producing forces, toxic chemicals or materials, harmful physical agents, ergonomic stressors, biologic orinfectious agents. Here, I present only the results of training aimed at reducing injury-producing forces. Alltogether, they found 80 studies that evaluated some kind of training intervention. These studies used eithersatisfaction, knowledge, behaviour or injuries as the outcome by which the effectiveness was judged. Ofthese 80 studies, 21 studies aimed at injury prevention but only 14 used some kind of control group. Thefollowing results were reported. Four studies reported a reduction of injuries and one study reported noeffect. Seven studies reported objective behaviour change and one no effect. The other studies measured onlyknowledge or satisfaction. The authors conclude that there was "much direct and indirect evidence to showthe benefits of training in establishing safe and healthful working conditions. The intervention studies inparticular were especially supportive. Findings here were near unanimous in showing how training can attainobjectives such as increased hazard awareness among the workers at risk, knowledge of and adoption of safework practices, and other actions that improve workplace safety and health protection." The review did nottake into account possible biases such as publication bias and the quality of included studies. It is unsure ifthe same conclusions would be drawn with current systematic review standards.More recently Burke et al reviewed the effectiveness of occupational health training with the specificobjective to see if training that engaged workers more was more effective than training in which workerswere less engaged 81. They used a meta-analytic approach mostly used in psychology and grouped all typesof training programmes together but looked separately at knowledge, performance and injury outcomes. Tobe included in the review, studies had to compare the intervention with a control group. They found 95studies of which 31 evaluated the effect on injuries. The authors did not mention an overall outcome of theirreview but only reported that the pooled effect sizes significantly increased from least engaging to 26
  27. 27. moderately engaging to most engaging training programmes for knowledge, and injury outcomes but not sofor behavioural outcomes. The latter non-significant result is explained by confounding as the level ofengagement was also related to the complexity of the behaviours that had to be improved. The more complextasks involved more worker engagement but were at the same time more difficult to change. The authorstook methodological quality partly into account but not publication bias.In 2010 a group of researchers from the Canadian Institute of Work and Health and NIOSH updated theNIOSH review with better methodology and newer studies.82 They were interested only in randomisedcontrolled trials and found 22 of these but included in the review only 14 which were judged as of sufficientquality. They categorized interventions as low, medium or high worker engagement and they categorisedoutcomes as knowledge, attitudes and beliefs, behaviours and health-outcomes. Based on the quality and theeffect size of studies in a category, evidence for effectiveness was assessed as strong, sufficient orinsufficient. There were only four studies with six interventions which fulfilled the inclusion criteria andwhich aimed at reducing safety outcomes. Only two of these measured health/injury outcomes and both hada non-significant outcome. The authors did not look at separate outcomes but combined all studies. Theyconcluded that there was insufficient evidence that knowledge was increased by training, strong evidencethat behaviour improved and again insufficient evidence that health outcomes improved. This somewhatcontradictory result is due to the lack of high quality studies in the knowledge domain even though the effectsize was large. The authors concluded also that there was insufficient evidence for a greater effect of trainingwith higher worker engagement. Behavioural safety interventions: feedback and rewardsWirth and Sigurdsson provided an overview of behavioural safety research without pretending that theoverview is systematic.83 The approach is based on behavioural psychology and applied already in the 1930s.They defined behavioural safety as "an approach designed to change safety-related behaviours directlythrough the application of behavioural principles and multiple strategies such as peer observations of safebehaviours, goal setting, performance feedback and celebrations or incentives for safety goals." They see thisas an additional approach to engineering controls. They found that evidence of effectiveness is mostlymissing but that many of the intervention ideas are useful and should be better evaluated. The authorsstressed the importance of feedback and incentives such as rewards and celebrations because they are animportant feature of behavioural psychology. The idea is that reinforcement is "a basic learning process thatoccurs when a behavioural consequence increases the frequency, intensity or duration of the targetedbehaviour".In an older review of the use of incentives and feedback to enhance workplace safety, McAfee and Winnaptly summarised 24 studies mostly carried out in the 1970s and 1980s.84 They included studies if they hadused an incentive intervention, a before-after outcome measurement and reported quantitative data. Most 27
  28. 28. studies were based on the principle that rewarded behaviour is likely to be repeated. The types ofinterventions used were monetary incentives, praise and feedback and team competitions. The authors foundthat all studies reported positive results in terms of a reduction of injuries in eight studies or an increase ofsafety behaviour in the other 14 studies at least in the short term. One study reported that a reward systemstill improved safety after having been in place for 12 years. Based on the results of their review they find itimpossible to tell which incentives were the best and they argue that better studies are needed to informpractice. Clinical: Pre-employment examinations for preventing injuriesThe Cochrane review on pre-employment examinations used earlier, included two studies that aimed atpreventing injuries. Based on the results of the pre-employment examinations, the studies divided jobapplicants in a group that were judged to be at risk and in a group that were not at risk.33 In one study, theapplicants that were at risk were provided with work accommodations. After one year of follow-up, theinjury rate in the group with work accommodations was similar to the group of job applicants that wereconsidered to be not at risk. This was taken as evidence of effectiveness of a beneficial effect of pre-employment examinations and work-accommodations. In another study in the military, a training programmewas offered to those that were judged to be not physically fit enough to endure military training withoutsustaining injuries. At the end of follow-up the injury rate in those who received training was similar to thosewho were judged not to be at risk. Also in this study, this was taken as evidence that the pre-employmentexamination with the training intervention was effective in reducing injuries in those at risk.However, the confidence intervals around the risk estimates were wide and included also a substantial higherrisk for those that were provided with workplace accommodations and training. Even though these studiesprovide some evidence that work-accommodation and training can be effective interventions with pre-employment examinations, the quality of the evidence was assessed as very low.3.5. Approaches to Small EnterprisesSmall enterprises form the majority of companies and a considerable part of workers are employed by smallcompanies. Small enterprises differ from bigger enterprises in that they are usually led by the owner who hasto handle all the management tasks. Halse and Limborg describe that the owner is usually suspicious aboutregulation and external consultants.23 The amount of resources that small companies are able and willing todevote to occupational safety and health is usually limited. In addition, injuries and accidents occur ratherinfrequently which easily leads to an ad-hoc approach in safety matters. The authors describe two approachesto meet the specific needs of small firms. One is to develop specific tools such as predefined checklists forrisk assessment for specific types of firms. The other one is to work with intermediary organisations thatsupport small enterprises such as labour unions, insurance companies or occupational health services. Theauthors acknowledge that none of these methods is based on thorough evaluation studies. 28
  29. 29. Brooke advocates a specific hazards-scheme approach towards the occupational health problems of smallfirms to control health risks from chemicals.85 Their approach is very similar to control-banding and alsobased on the idea that it is much easier to work with hazard bands than to measure all exposures. Theypropose to create the hazard bands based on the R-phrases that are required based on EU-regulation. Anevaluation of the hazard scheme to occupational exposure limits showed that the scheme is a potentiallypowerful tool for helping SMEs to control chemical risks. However, there is no evaluation that shows if risksin practice are more effectively controlled using the hazard-scheme.One systematic review focussed entirely on safety interventions for businesses with less than 100 employees.The review included five studies that covered a wide range of varying interventions. The interventions werefound to be effective in increasing safety-related attitudes and beliefs but had mixed effects on exposure andno effect on health outcomes. It was difficult to draw conclusions that were specific for small firms from thisreview.864. Conclusions and discussionTable 2 summarises the evidence that I found for the effectiveness of essential primary preventiveoccupational safety and health interventions. The general conclusions are that there is evidence fromsystematic reviews that: - many technical interventions for inhalation exposure reduction are effective and do not necessarily have to be costly and can be based on simplified exposure assessments such as control-banding - there is indirect evidence that shows that specific ventilation controls are better than general controls - regulation and incentives for employers are probably one of the main causes of inhalation exposure reduction in the industrialised world in the past forty years. It is therefore concluded that regulation and incentives are effective in implementing technical exposure controls in firms. - personal protective equipment can reduce exposure in a technical sense but there are many practical barriers that impede its effectiveness in practice - personal protective equipment is not a reliable tool without proper instruction and adaptation. This holds for both respiratory and for hearing protection equipment - that pre-employment examinations might prevent occupational asthma for specific exposures, even though the quality of the evidence is very low - regulation and enforcement can reduce noise levels in workplaces - hearing loss prevention programmes that are mainly based on hearing protection are probably not sufficiently protective even though the quality of the evidence is low - there is no evidence in the available studies that back pain can be prevented neither by training and education nor by ergonomic improvements nor by pre-employment examinations - technical passive hazard controls such as roll-over protection structures on tractors can reduce fatal injuries but for most technical controls there are no studies or no systematic reviews - regulation and incentives for employers for reducing injuries produce mixed results but there are no systematic reviews of measures to improve the safety climate in a company 29
  30. 30. - incentives such as feedback and rewards for workers improve safety behaviour and probably reduce injuries- education and training to prevent injuries produces mixed results with some reviews providing evidence of effectiveness but with other reviews not providing such evidence.- pre-employment examinations which lead to work accommodations or extra training might lead to lower injury rates 30