Thermal Heat Stress Occupational Hygiene – A Practical Approach

Kristy Thornton Occupational Hygienist

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

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

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

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

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.

Thermal Risk Assessment Process

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

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

Step 1: Basic Thermal Risk Assessment

Step 1: Basic Thermal Risk Assessment

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).

Basic Thermal Risk Assessment

Basic Thermal Risk Assessment

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.

28 60

Review assessment

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.

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.

TWL Outputs

TWL Outputs

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

Physiological Monitoring example

Level C PPE

•  Encapsulating Suits •  Gloves •  Gumboots •  Hard hat •  Full face Respirator

Methodology

•  ISO9886 (2004) –  Heart Rate –  Core Body Temperature

•  AIOH Heat Stress Standard

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

Hydration Testing

Results – Physiological Monitoring

Results - Hydration

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

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

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

Conclusion •  Stage 1: Basic Thermal Risk

Assessment •  Stage 2: Comprehensive

Investigation •  Stage 3: Physiological

Monitoring

•  AIOH Document can be obtained from https://www.aioh.org.au/downloads/forms/pubs_order_form.pdf

•  Basic Thermal Risk Assessment app https://itunes.apple.com/us/app/thermal-risk/id867920824?ls=1&mt=8

Contributors •  Kate Cole –

Manager Occupational Hygiene

•  University of Wollongong – Master Science (Occupational Hygiene)

•  Vinod Gopaldasani – University of Wollongong