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Management of Environmental Heat Stress

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Presentation to the Gladstone Industry Area Network, 3 December 2013

Presentation to the Gladstone Industry Area Network, 3 December 2013

Published in: Health & Medicine, Business

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  • 1. Management of environmental heat stress Christine Killip Atmospheric Scientist and Managing Director of Katestone
  • 2. Questions • Who has experiences excessive heat at work? • Who has a Heat Stress management policy? • How often is the policy used? • Which heat stress index is used? • Who thinks they could be doing more to manage heat stress?
  • 3. Is heat stress important for humans? • Currently 1100 deaths due to heat per year in Australia • Small number of workers have died due to heat stress in recent years • Significant impact on labour rates • Maloney et al (2011) projected the number of “dangerous” days will increase from 1 to 21 in 2070 for an acclimatised person doing physical labour and 17 to 67 days for an unacclimatised person
  • 4. Which is worse for heat stress? 36°C Temp 28°C Temp & & 30% RH 85% RH 42°C Temp 32°C Temp & & 20% RH 70% RH Based on Humidex
  • 5. The human thermal balance M + W = K + R + C + Cres + E + Eres +S -ve Metabolic (M) Convection (C, Cres) Evaporation (E, Eres) Ref: ISO 7243 +ve Conduction (K) Radiation (R) Mechanical (W)
  • 6. How do we keep our balance? • In light work or cool environments we dump metabolic heat by radiation and convection • But as work becomes heavier or environments warmer we become increasingly dependent on evaporative cooling • Result – we are vulnerable to anything that restricts evaporation (e.g. clothing, high humidity, or low air movement)
  • 7. How do we keep our balance? “Unrestricted evaporation of sweat lets healthy people cope — without ill effect or even marked discomfort — with air temperatures of 100 ◦C in saunas and 50 ◦C in deserts, and with more than a kilowatt of metabolic heat in strenuous activity.” Budd (2008)
  • 8. Overloaded system Level of heat tolerance reached Body temp rises Cardiovascular strain Sweat increases (dehydration) Weak Dizzy Clumsy Sick Heat exhaustion Heat stroke Adverse effects become likely when our behavioural responses are not allowed to function normally
  • 9. Guidelines Metabolic + Environment Ability to dissipate load in current environment
  • 10. 4 elements of our EHL Wind speed Radiation Temperature Humidity EHL
  • 11. How hot is too hot? • In 1947 Schickele plotted 157 heatstroke deaths in military training camps against temperature and humidity • Identified the ‘heat death line’ • Air temperatures ranging from 26 to 49 ◦C and relative humidities of 10 to100% • She commented that ‘Death can occur at surprisingly low temperatures, provided the evaporative power of the air is sufficiently reduced’
  • 12. Factors impacting human response to EHL Fitness Acclimatisation Age Dehydration Clothing PPE Weight Human response General health
  • 13. Heat Stress Indices • Rational indices are based upon calculations involving the heat balance equation (e.g. Swreq, TWL) • Empirical indices are based on establishing equations from the physiological responses of human subjects (e.g.ET) • Direct indices are based on measurement (usually temperature) used to simulate the response of the human body (WBGT index)
  • 14. Which index? • Currently over 67 different indices and growing • Each have boundaries for application • New ones always find ways to criticise the old ones • Complex ones are hard to apply • Easy ones tend to get used – but can be misused
  • 15. Which index? Solution: •Pick an index you are comfortable with •Understand its limitations •Use it as a guide only •Personal awareness is the key
  • 16. Example of using WBGT • • • • Developed by US Military in 1950’s Most widely used heat stress index Measures all 4 elements of EHL Based on hydrated, fit men in olive green long pants and t-shirts Ref: G. Budd WBGT – its history and limitations. Journal of Science and Medicine in Sport (2008) 11, 20—32
  • 17. WBGT reference values from ISO 7243 Metabolic rate M (Wm–2 ) Reference value of WBGT (°C) Acclimatised Not acclimatised 0. Resting M≤65 33 32 1. 65<M≤130 30 29 2. 130<M≤200 28 26 No sensible air movement Sensible air movement No sensible air movement Sensible air movement 3. 200<M<260 25 26 22 23 4. M>260 23 25 18 20 Note: The values given have been established allowing for a maximum rectal temperature of 38°C for the persons concerned.
  • 18. Work/rest regimes Work Demands Acclimatised workers Light Moderate Heavy Very Heavy 100% work 29.5 27.5 26.0 75% work / 25% rest 30.5 28.5 27.5 50% work / 50% rest 31.5 29.5 28.5 27.5 25% work / 75% rest 32.5 31.0 30.0 29.5 recommended by the ACGIH (1996) based on the WBGT values in °C
  • 19. WBGT Limitations • Commonly misused and “estimated” from not standard instruments • Wind speed is not adequately accounted for as a cooling mechanism • Underestimates the heat stress in restricted evaporation conditions • e.g. clothed men alternately exercising and resting for 4 h in hot, humid conditions tolerated ‘with ease’ when WS was 0.8 m/s became incapacitated when WS dropped to 0.1 m/s (only a 0.2 increase in WBGT)
  • 20. CAUTION: If WBGT is used as a “screening” level assessment it may not actually indicate the extreme level of heat stress likely if sweating is the only mechanism to dissipate heat
  • 21. When WBGT isn’t actually WBGT • WBGT without the GT is not WBGT • published in 1980’s by American College of Sports Medicine, and widely used including BOM • Measurement by hand held instruments (physically impossible to get it right!)
  • 22. Is heat stress currently being taken seriously? • Singh et al (2013) interviewed 20 Australian industries to answer: – Is excessive heat exposure an existing threat to health of working people in the Australian context? – What are the prevailing attitudes towards heat exposure and heath protection in high heat exposure occupational groups in Australia?
  • 23. Study finding • 95% experienced excessive heat at work • 75% experienced heat exhaustion at work • 35% indicated heat exhaustion was frequent • 100% indicated that heat caused a loss in productivity
  • 24. Study finding “During summer most calls to our workers disputes hotline are related to heat” Union Representative “We often hear managers claim that heat exposure is simply part of working in this industry, so workers just have to deal with it and continue” Union Representative
  • 25. Heat and Accidents • Increased accident rate in construction industry during summer months • Prof Rowlinson et al (2013) proposed that management of heat stress through work rest regimes can result in increased productivity • Ramsey et al (1983) produced a relationship between unsafe behaviour and temperature
  • 26. Ramsey et al (1983) Effects of workplace thermal comfort on safe work behavior. Journal of safety Research, Vol. 14, pp. 105-114, 1983
  • 27. Acclimatisation • Is a complex physiological process where the body adjusts as a response to the thermal environment • Physiological changes include: – cardiovascular stability, fluid and electrolyte balances, sweat rates and temperature responses • Exposure to heat does not confer acclimatisation • Elevated metabolic rate for about 2 hours per day, to achieve acclimatisation, is required
  • 28. How long does it take to acclimatise? • Gradually gained over weeks (up to 21 days) • Can be lost even over a weekend (only small amounts) • Acclimatisation to one level of heat stress does not indicate acclimatisation at a higher heat stress level
  • 29. Learnings • The human response to heat stress is complex with lots of factors to consider • Heat stress can cause problems before it becomes a serious health issue (e.g. Impaired cognitive ability) • Heat stress management involves: – environmental heat load – job requirements (e.g. PPE, radiant heat source, work load) – human factors (e.g acclimatisation, hydration) • Heat Stress indices are great in number and have been widely misused
  • 30. For your consideration • Are workers in the field as well protected as those in well documented high heat stress areas inside? • What happens when the EHL changes? Are thermal heat risk assessments updated? • Do we know when the highest EHL occurs? • Would better understanding of EHL forecasts allow you to plan your work schedules?
  • 31. Weather intelligence
  • 32. What is • online environmental management system • designed to provide state-of-the-art weather and climate analytics • to assist you to proactively manage activities • by providing location specific weather forecasts, extended outlooks and climate projections • tailored to your specific business location and activities
  • 33. Overloaded system Heat stress can cause significant loss in productivity before we reach our level of heat tolerance Body temp rises Cardiovascular strain Sweat increases (dehydration) Weak Dizzy Clumsy Sick Heat exhaustion Heat stroke
  • 34. Benefits • Reduce weather risk • Optimise operations through better planning for work/rest regimes • Protect worker through heat stress management before it causes additional problems (e.g. increase in accidents) • Simplify your workload through easy to interpret dashboard (red/orange/green)
  • 35. Features • High resolution local forecast for anywhere in Australia (4 days, hourly timestep) • Extended 14 day outlook • Seasonal outlook • E-mail or sms alerts • Latest situation updated by meteorologist for high risk events
  • 36. Behind the scenes • Customisable index to meet your application (e.g TWL, DustX, Inversion) • Increase accuracy by uploading your own data • Robust and fully backed up data system for data security
  • 37. The Katestone forecasting system Observations AWS Ships Aircraft Balloons Buoys Satellites Central collection World Met Office (WMO) data store Worldwide Millions of sites Decades of data International Global Model GFS Worldwide 0.5 Deg Resolution 7 Days @ 3 hour intervals Katestone (K-WRF) BOM AWS Observations WRF-ARF 12 Km resolution Australia wide 4 days in 1 hour intervals Research On site AWS Email and SMS Alerts
  • 38. Accurate information Model Parameter (1 day out) Statistic Value (°C) Comment K-WRF Temp RMSE 2.17 2012/13 all sites K-WRF Temp RMSE 1.61 2012/13 Zone 11 ACCESS-A Temp RMSE 2.2 Bridge et al, 2011 K-WRF Temp MAE 1.68 2012/13 all sites K-WRF Temp MAE 1.23 2012/13 Zone 11 US-NWS (Human) Tmax and Tmin MAE 1.47 Wheeler et al 2011 GFS+MOS Tmax and Tmin MAE 1.53 Wheeler et al 2011 K-WRF MAE for Temp remains below 2°C out 3 days
  • 39. Weather intelligence
  • 40. Thank you Please e-mail any questions to christine@katestone.com.au Katestone PO Box 2217 Milton, QLD, 4064
  • 41. References • • • • • • Gaughan et al., 2008. A new heat load index for feedlot cattle. Journal of Animal Science, vol. 86 no. 1 226-234 Bureau of Meteorology and CSIRO (2010) State of the climate Hanna, E.G., Kjellstrom, T., Bennett, C. and Dear, K. (2011) Climate Change and rising heat: population implications for working people in Australia. Asia Pacific Journal of Public Health, 23 (2 Suppl.), 14S-26S Parson, K (2003) Human Thermal Environments – The effects of hot, moderate and cold environments on Human Health, Comfort and Performance. Taylor & Frances, London Maloney, S. and Forbes, C. (2011) What effect will a few degrees of climate change have on human heat balance? Implications for human activity. International Journal of Biometeorology, 55, 147. Ollie, J. and Kenny G. (2010) Heat Exposure in the Canadian Workplace. American Journal of Industrial Medicine 53:842–853 (2010)
  • 42. • • • • • • • International Standard (1989) ISO 7243 Hot Environments – estimation of the heat stress on working me, based on the WBGT-index (wet bulb globe temperature) Budd, G. (2008) Wet-bulb globe temperature (WBGT) - its history and its limitations . Journal of Science and Medicine in Sport (2008) 11, 20-32 Schickele E. (1947) Environment and fatal heat stroke - an analysis of 157 cases occurring in the army in the U.S. during World War II. Milit Surg 1947;100:235-56 Ramsey et al (1983) Effects of workplace thermal comfort on safe work behavior. Journal of safety Research, Vol. 14, pp. 105-114, 1983 ACGIH (1996) TLVs and BEIs. Threshold Limit Values for chemical substances and physical agents. Biological Exposure Indices. American Conference of Governmental Industrial Hygienists, Cincinnati, OH. Singh, S. Hanna, E. Kjellstrom, T. (2013) Working in Australia’s heat: health promotion concerns for health and productivity Steve Rowlinson, Andrea Yunuan Jia, Baizhan Li, Carrie Chuanjing Ju (2013) Management of climatic heat stress risk in construction: A review of practices, methodologies, and future research. Accident Analysis and Prevention (unpublished)