4. Things just keep getting better


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The fourth presentation for a workshop in Singapore and AIOH2013

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  • In a review of published evidence for temporal trends that we published in 2007 we identified 38 cases where there was informative data for aerosols. We analyzed the temporal trends on the log-scale assuming an exponential decline in exposure level over time. 58% of these involving aerosols there was a significant reduction in exposure, typically between 5% and 10% per year. Only one dataset (3%) showed a significant increase.
  • For gases and vapours there was a similar pattern, in this case with 56% of cases showing a significant decrease in exposure – none showed a significant increase. Overall the median decrease in level was 7% per annum.
  • In an individual plant it might be assumed that over time there are periodic changes to the production process that give rise to a reduced exposure. For example in this case there are three changes in the second, third and seventh years, in each case exposure being reduced by at most 50%, although as time goes on the reduction gets smaller to reflect the possibility that it gets more difficult to control exposures. We can further explore the impact of changes over time in a group of plants with a Monte Carlo simulation – in this case we allow the interventions to take place at random with a decision each quarter – 10% chance and on each occasion a 50% chance that it would reduce exposure. The initial level being set at random between 10 and 300 mg/m3.
  • With five plants you see quite a variable pattern of intervention. On average about one intervention every two years in a plant.
  • Ten plants
  • By the time you have 25 plants the average exposure declines exponentially, in this case with a decrease of about 11% per year.
    Clearly to achieve the level of change that we noted in the review you do not need anything other than a low level of modest interventions.
  • Of course not every situation presents a decreasing profile and perhaps the most striking example that we have identified is for flour dust in Britain, where we find a complete absence of any temporal trends looking at data covering about the last 25-years.
  • The most extreme reduction is from the PVC plants in the early 1970s when the risk of angiosarcoma of the liver was first identified as a consequence of high VCM exposure. Here over a about a year the exposure dropped by more that an order of magnitude. Interestingly, although there was not systematic monitoring data for the period prior to the dramatic change the evidence is that there were improvements taking place before this which would have given a series of modest reductions in exposure and after about 1975 the rate of decline in exposure again dropped to about 6% per annum.
  • The changes that were taking place around this time were partly improvements in the process, for example adding scale inhibitors to reduce the adhesion of PVC to the autoclave walls and partly retrofitted engineering controls, such as local ventilation, or PPE such as BA.
  • Returning to our investigative studies, we have carried out interviews with process managers in about 30 companies where we collected data to quantify time trends in exposure. Here the average exposure change was between about 4 and 8% average decrease per year. These data were obtained by revisiting companies that had previously been investigated ten or more years previous. Note, we identified a greater reduction in toluene in our routinely collected data but this was probably as a consequence of removal of toluene from products rather than company specific changes.
  • In our companies there were several factors that were important including retrofitting local controls, as for example in this situation where a slot ventilation system was added to a mixing machine.
  • From our questions we identified several reasons for change, but we have grouped these into economic, legislation-related and safety culture related. For example, …MORE
  • It can be seen that legislative explanations predominated, followed by economic factors and the safety culture.
    However, the relative importance of these differed between sectors with legislative being most important in quarries, economic in wood and safety culture in industries using solvents containing toluene.
    This data is helping to guide us in the development of a TPB questionnaire to explore these factors more widely.
  • Exposure levels were 13 times higher in 1965 than in 2000 and declined at a rate that varied from 4 to 15% per year from 1965 to 1985, followed by a small peak in the mid-1990s.
    While this peak likely represents a period of higher exposure levels coinciding with Chinese economic reforms starting in the late 1980s through the beginning of the 1990s, it may also be (partially) a data artifact from changes in sampling method, analytical method or measurement strategy
  • Now, the Theory of Planned Behaviour is a successful approach used to understand individual behaviour. It is based on the assumption that behaviour is directly linked to our expressed intention to act in a given situation, of course influenced by our abilities (the actual behavioural control) – there is no possibility that despite my intention to be a successful concert pianist that I will ever be able to play the piano. In addition, according to the Theory there are three other areas of our attitudes and beliefs that influence our intention to act – control beliefs and our perceptions of the ease or difficulty in performing that action (here control is in the sense of control over the behaviour). Subjective norms relate to our perceptions of the social pressures to act, and beliefs about the consequences of a behaviour and outcome evaluations in terms of the desirability of the behaviour.
    16 arrowheads, I think.
  • 4. Things just keep getting better

    1. 1. Things just keep getting better John Cherrie nt I wa to TE IN A ELIM place work c can er INSTITUTE OF OCCUPATIONAL MEDICINE . Edinburgh . UK www.iom-world.org
    2. 2. Summary… • • • • Exposures change over time, almost always decreasing What is the evidence for this? Why are companies acting to reduce exposures? Is it true for all substances in every country?
    3. 3. Exposure decreases over time… Aerosols Creely KS et al. (2007) Trends in inhalation exposure--a review of the data in the published scientific literature. Ann Occup Hyg.; 51(8): 665-678.
    4. 4. Exposure decreases over time… Gases and vapours Creely KS et al. (2007) Trends in inhalation exposure--a review of the data in the published scientific literature. Ann Occup Hyg.; 51(8): 665-678.
    5. 5. Exposure decreases over time… Fibres Creely KS et al. (2007) Trends in inhalation exposure--a review of the data in the published scientific literature. Ann Occup Hyg.; 51(8): 665-678.
    6. 6. Let’s do a thought experiment… • • Start with a singe factory and follow it’s progress in controlling exposures over 10 years Repeat at different plants and see how the pattern builds up
    7. 7. Simulated exposure reduction at a plant
    8. 8. Five plants…
    9. 9. Ten plants…
    10. 10. 25 plants…
    11. 11. Flour dust… van Tongeren M et al. (2009) Trends of flour dust exposure in the United Kingdom, 1985–2003 Environ. Monit., 2009, 11, 1492 – 1497.
    12. 12. VCM levels in a English PVC plant 12
    13. 13. What changes? • • • • • • • • High pressure water jet cleaning Removal of VCM residues by stripping Improved general ventilation Use of scale inhibitors Extraction on open reactor vessels Reduce leaks Air monitor Breathing Apparatus
    14. 14. Investigation of changes in exposure… Galea KS et al. (2009) Trends in Wood Dust Inhalation Exposure in the UK, 1985–2005. Ann.Occ.Hyg.
    15. 15. Things changed…
    16. 16. What were the determinants of change? • Economic • • • Legislation • • • Market downturn – reduced production, less people Improved efficiency – buying in ready-made components Environmental – achieve emissions targets Health and safety – inspection visits, prosecution Safety culture • • New owners – larger company New managers – new ideas
    17. 17. What were the determinants of change?
    18. 18. Is this a “universal truth”! Benzene levels in China Friesen MC et al. (2012) Combining a Job-Exposure Matrix with Exposure Measurements to Assess Occupational Exposure to Benzene in a Population Cohort in Shanghai, China. Ann Occup Hyg;56:80–91.
    19. 19. Time trends in exposure… Rubber - Crude Materials, Compounding and Mixing 18.0 Netherlands United Kingdom Poland Germany Sweden 16.0 14.0 10.0 8.0 6.0 4.0 2.0 20 10 20 05 20 00 19 95 19 90 19 85 19 80 19 75 19 70 0.0 19 65 mg/m3 12.0 Time trend per year UK : -6% NL : -2% PL : -6% SW : -6% GE : -7% http://exasrub.iras.uu.nl/content.html Agostini et al. Exposure to rubber process dust and fume since 1970s in the UK; influence of origin of measurement data. J. Environ. Monit. (2010) vol. 12 (5) pp. 1170
    20. 20. But not always! Vermeulen R, Coble JB, Lubin JH, et al. The Diesel Exhaust in Miners Study: IV. Estimating Historical Exposures to Diesel Exhaust in Underground Non-metal Mining Facilities. Ann Occup Hyg 2010;54:774–88.
    21. 21. The Theory of Planned Behaviour Behavioural beliefs Attitude towards the behaviour Normative beliefs Subjective norms Control beliefs Perceived behavioural control Intention Behaviour Actual behavioural control http://people.umass.edu/aizen/tpb.diag.html
    22. 22. Summary… • • • • In most situations exposure appears to decrease over time by between about 5% and 15% per annum Modestly effective controls implemented every three or four years is sufficient to explain these trends The most likely explanation is improving manufacturing efficiency There are some exceptions to the rule!