Kristy Thornton - Thiess - Occupational Hygiene


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Kristy Thornton delivered the presentation at the 2014 Safety in Action Conference Sydney.

The 2014 SIA Sydney Safety Conference at Sydney Olympic Park featured a wide range of practical case studies directly from the organisations involved with developing their health, safety and wellness protocols. Learn from their experiences and take back techniques for the enhancement of your own WHS policy.

For more information about the event, please visit:

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Kristy Thornton - Thiess - Occupational Hygiene

  1. 1. Thermal Heat Stress Occupational Hygiene – A Practical Approach Kristy Thornton Occupational Hygienist
  2. 2. Overview – Thermal Heat Stress • What is thermal heat stress? • AIOH Risk assessment tool o Stage 1 o Stage 2 o Stage 3 • Practical Examples • Key learnings
  3. 3. What is Thermal Heat Stress? The heat “load” that a worker may be exposed to from performing their work, environmental factors (ie: air temperature, humidity, air movement and radiant heat) and clothing requirements
  4. 4. Heat illnesses Heat Strain: • Heat Rash (Prickly Heat) • Heat Cramps Heat Exhaustion • Clammy, moist skin • Excessive sweating Heat Stroke • Hot, dry skin • Shivering, convulsions Without initial prompt medical attention, heat stroke can be fatal
  5. 5. Higher Risk Groups Some groups of workers are at a higher risk of developing a heat-related illness such as: • Physically unfit workers • Overweight or obese workers • Elderly workers • Workers with heart conditions • Alcohol and drug consumption • Some medication such as diuretics • Dehydrated workers • Smokers • Unacclimatised workers
  6. 6. Acclimatisation • Allowing yourself time to acclimatise to the hot conditions. ie: don’t over do it on Day 1! • Approx. 1 week of gradually increasing the workload and time spent in the hot environment • Heat acclimatisation involves a series of physiological modifications which occur after you have been exposed to heat over time. • It is acquired naturally and slowly over a period of several days (sometimes weeks) of continued activity in the heat. • Once you are acclimatised you may find that you sweat less and your resting heart rate lowers.
  7. 7. Thermal Risk Assessment Process
  8. 8. How to Assess the Risk? 1. Basic Thermal Risk Assessment a) Incorporates WBGT measurements b) Task complexity c) Distance from cool rest area and drinking water d) Clothing factors e) Air movement f) Acclimatisation • Determines if a potential risk exists and highlights control measures to be put in place to reduce the risk. • Determines if further analysis is required
  9. 9. How to Assess the Risk? 2. Comprehensive Investigation a) Incorporates further analysis of radiant heat load, air velocity, humidity, clothing, metabolic load, posture and acclimatisation b) Develops work / rest regimes if necessary to calculate an ‘allowable exposure time’ 3. Physiological Monitoring a) Performed by an Occupational Hygienist b) Used where high-level PPE (impervious clothing) is utilised and/or; c) Where the calculated allowable exposure time is less than 30- minutes
  10. 10. Step 1: Basic Thermal Risk Assessment
  11. 11. Step 1: Basic Thermal Risk Assessment
  12. 12. Basic Thermal Risk Assessment • Measure the Wet Bulb Globe Thermometer (WBGT) temperature for the work activity and tick the appropriate box. • Provide a value for ‘SUB-TOTAL C • Wet Bulb Globe Temperature can be obtained from the nearest Bureau of Meteorology station to site (if no monitor is available and the work is performed outdoors).
  13. 13. Basic Thermal Risk Assessment
  14. 14. Basic Thermal Risk Assessment 28 60 Low Risk Medium Risk High Risk If the Assessment Point Total: • < less than 28 = risk of thermal conditions is low. • > above 28, then a review should be performed to lower the risk where possible. • > 60 then Step 2 is needed. • Step 3 is always needed where impermeable chemical protective clothing is used.
  15. 15. Review assessment
  16. 16. Step 2: Comprehensive Investigation • Performed where Step 1 shows that further analysis is required ie: Score >60 points • The Thermal Work Limit (TWL) can be used for this assessment as long as workers are hydrated and able to self pace there work activities.
  17. 17. Thermal Work Limit (TWL) • The maximum sustainable metabolic rate that hydrated, acclimatised individuals can maintain in a specific thermal environment, within a safe deep core body temperature (<38.2ºC) and sweat rate (<1.2 kg/hr). • Based on underground mining conditions and was developed in the Australian climate. TWL has been selected as it is designed specifically for self-paced workers and does not rely on estimation of actual metabolic rates. The TWL uses five environmental parameters: • Dry bulb • Wet bulb • Globe temperature • Wind speed • Atmospheric pressure • The TWL uses clothing factors to predict safe maximum continuously sustainable metabolic rates for the conditions being assessed.
  18. 18. TWL Outputs
  19. 19. TWL Outputs
  20. 20. Step 3: Physiological Monitoring • Used where high-level PPE (impervious clothing) is utilised and/or; • Where the calculated allowable exposure time is less than 30-minutes • Performed by a Competent Occupational Hygienist • Involves assessing an individual’s exposure and response to heat stress by collecting measurements of heart rate and core body temperature
  21. 21. Physiological Monitoring example
  22. 22. Level C PPE • Encapsulating Suits • Gloves • Gumboots • Hard hat • Full face Respirator
  23. 23. Methodology • ISO9886 (2004) – Heart Rate – Core Body Temperature • AIOH Heat Stress Standard
  24. 24. Physiological Monitoring Criteria • Heart Rate Limit = 185 – 0.65A (A = age in years), sustained for a period ≥ 10 minutes • Maximum core body temperature of > 38.5◦C for > 10 minutes
  25. 25. Hydration Testing
  26. 26. Results – Physiological Monitoring
  27. 27. Results - Hydration
  28. 28. Physiological Monitoring Conclusion • Workers were able to self pace • Physiological monitoring showed workers were able to conduct works within this environment without an increased risk of developing heat stress • Workers took place in self testing for hydration • Workers participated in heat stress training
  29. 29. Control Measures • Elimination of source of heat such as: 1. Shielding of radiant sources 2. Reduction of plant and pipework temperatures • Moving the work from being performed outdoors or underground to inside an air-conditioned building • Ventilation • Artificial Cooling • Performing work in enclosed air-conditioned cabins
  30. 30. Controlling the risk • Start work early in the cooler part of the day • Plan upcoming work by taking into account the weather forecast • Implementing work/rest regimes • Rotation with co-workers • Awareness training provided to all workers • Allowing workers to acclimatise to conditions • Provision of cool water and cool rest areas • Electrolyte drinks (in moderation) • Reduction in the use of PPE • Wear long length clothing that is made from a close weave fabric that allows for air circulation and the evaporation of sweat. • Providing cool vests to workers
  31. 31. Conclusion • Stage 1: Basic Thermal Risk Assessment • Stage 2: Comprehensive Investigation • Stage 3: Physiological Monitoring • AIOH Document can be obtained from downloads/forms/ pubs_order_form.pdf • Basic Thermal Risk Assessment app thermal-risk/id867920824? ls=1&mt=8
  32. 32. Contributors • Kate Cole – Manager Occupational Hygiene • University of Wollongong – Master Science (Occupational Hygiene) • Vinod Gopaldasani – University of Wollongong