Heat Stress Monitoring - OHSA Occupational Health Services Australia

Heat Stress Monitoring Surveys

Severe and extreme heatwaves in Australia have caused more deaths than any other natural disaster in the last 200 years according to the Australian Bureau of Meteorology. The official death toll of the 2009 Victorian Black Saturday bushfires was 173, but 374 people died from heat-related causes during the heatwave that preceded it.

OHSA has conducted heat stress monitoring at a variety of workplaces including:

• Mining – Hot Work Areas
• Smelters – Boiler Fabrication & Maintenance Work
• Food Preparation – Yes we thought it was initially strange as well!
• Electrical Distribution – Tower & Pole Climbing
• Manufacturing – Welding inside tanks in humid tropic climates

There is no workplace exposure standard or limit for heat stress.

Setting of a safe/unsafe limit simply based on ambient air temperature is not appropriate due to the many variables (i.e. task, environment and individual) associated with the onset of heat strain. as guides.

Identification and assessment

Identifying and managing heat stress is not just about the air temperature. Assessing risks of heat related illness requires accurate identification and assessment of:

• workplace conditions
• job requirements
• individual worker attributes.

Conduct a walk through survey of the workplace, and ask your workers about their heat stress issues. Consider the work location’s previous history of heat stress issues, including what time of day or year and under what circumstances they occurred.

Some standard questions in any heat investigation include:

• What are the potential sources of heat?
• What heat stress problems have been experienced?
• What type of action has the worker taken to minimise his or her exposure to thermal energy?
• Is there a thermal stress management program in place?
• Does it include awareness training and information on heat stress?
• What type of remedial action has been taken to reduce the site’s thermal loading to workers?
• What comments or concerns have been raised by workers?

Use the following three level approach to identify heat stress factors in your workplace (Di Corleto et al 2013).

Level 1 (Non-technical): is a basic risk assessment, which can use a simple index such as the Heat stress (basic) calculator.

Heat Stress Flow Chart

Heat stress (basic) calculator is a simple online tool designed for use by anyone with basic knowledge of the work area and process. There is no direct measurement of environmental conditions required to use the calculator.

The online calculator uses a number of factors to make a basic assessment of heat stress including:

• the state of acclimatisation
• work demands, location
• clothing
• sun exposure
• hot surfaces
• task complexity
• air movement, and other factors
• apparent temperature (this is calculated using ambient temperature and relative humidity).

Note: As the basic assessment is a qualitative assessment, instrumentation for measurement of wet bulb glove temperature (WBGT) is not mandatory meaning people with limited technical expertise and equipment can identify and assess the risk factors. The basic assessment can therefore be performed using readily available information at the workplace (i.e. ambient air temperature and relative humidity).

The online calculator is an initial qualitative review of potential heat stress situations and is not a definitive assessment tool.

A level 2 (technical) assessment will be needed when:

• the online calculator identifies an unacceptable level of heat stress risk
• impermeable clothing is worn.

Level 2 (Technical): needs additional data collected and the use of a second level index such as ISO 7933: Predicted Heat Strain (PHS) or Thermal Work Limit (TWL). A range of measuring equipment and expertise is required for this type of assessment.

Additional data needed for this type of assessment will include:

• dry bulb temperature
• globe temperature
• air velocity
• humidity
• metabolic load
• clothing type

This type of assessment and gathering of required data should only be undertaken by a competent person such as an occupational hygienist or occupational physician.

A level 3 (expert) assessment will be needed when either:

• data cannot be collected
• where impermeable clothing is used.

Level 3 (Expertise): Physiological monitoring

Physiological monitoring is used in cases of high heat stress risk such as:

• work involving the use of encapsulating suites (e.g. hazmat suits) or high levels of external PPE
• environments where the level 2 assessment indicates allowable exposure times of less than 30 minutes
• where a work environment cannot be accurately assessed.

The risk and severity of heat related illness will vary widely among workers, even under identical heat stress conditions. Individual monitoring measures a worker’s physiological responses (such as elevated body temperature and/or heart rate) to assess the effectiveness of implemented controls.