Post on 20-May-2015
description
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