Government of Western Australia Department of Mines and Petroleum Please read this before using presentation This presentation is based on content presented.

Government of Western Australia Department of Mines and PetroleumGovernment of Western Australia Department of Mines and Petroleum

Please read this before using presentation

• This presentation is based on content presented at the Exploration Safety Roadshow held in August 2009

• It is made available for non-commercial use (e.g. toolbox meetings) subject to the condition that the PowerPoint file is not altered without permission from Resources Safety

• Supporting resources, such as brochures and posters, are available from Resources Safety

• For resources, information or clarification, please contact:[email protected]

or visitwww.dmp.wa.gov.au/ResourcesSafety

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Toolbox presentation:

Heat Stress

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Outline• Thermoregulation• Heat gain, storage and loss• Heat strain and related illnesses• Risk factors for heat strain• Risk assessment and control

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Normal body temperature

Optimal conditions for cellular reactions in the human body include a core body temperature of approximately 37°C

Thermoregulation

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Thermoregulation

• Heat sensors in the skin and body – transmit “information” to hypothalamus in the brain, which directs an increase in heart rate, vasodilatation and sweating

• Sweat loss may be as high as 1.5 litres per hour

• Evaporation of one litre of sweat can be equivalent of 670 watts of energy – highly effective

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Heat gain, storage and loss

Heat inputs• Heat production – from metabolic activity or work intensity

• Heat storage – due to insulation of the “inner core”

• Heat gain – from external heat sources (radiation and convection)

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Physics of heat transfer• Conduction – transfer of heat between two materials from high to

low heat energy areas• Convection – bulk transfer of heated matter from warm low

density regions via a moving fluid (gas or liquid) to cooler more dense areas

• Radiation – process of heat transfer over distance between surfaces (particularly at the infrared wavelength)

• Evaporation – warmer molecules gain sufficient energy to leave the liquid surface and enter the gaseous phase. Remaining molecules have less average kinetic energy, resulting in decrease in temperature of liquid

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Thermal balanceBody must balance the heat transferred into the body, heat

generated in the body and heat dissipated to the environment

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Heat strain and heat related illness

Heat stress and heat strain• Heat stress – sum of environmental influences (air temperature,

radiant heat, humidity, air velocity) that, when coupled with metabolic heat generation and effects of clothing, may result in heat strain

• Heat strain – physiological response to heat stress on the body

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Heat illness• Heat oedema – mild form of heat illness resulting in pooling of

fluid in legs brought about by transient peripheral vasodilation• Heat rash – skin that has been persistently wetted by sweat may

develop a rash characterised by raised lumps that may be intensely itchy. Bumps caused by blocked sweat glands, which subsequently burst, causing a stinging sensation

• Heat fatigue – additional blood is diverted to skin as result of peripheral vasodilatation, reducing output to the brain and internal organs, and resulting in fatigue and reduction in strength

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Heat illness (continued)

• Heat cramps – painful involuntary muscle spasms resulting from electrolyte dilution arising from hard work in hot environments, heavy sweating and excessive water intake

• Heat syncope – dizziness or fainting brought about by lowered blood pressure arising from vasodilatation and pooling of body fluids into legs and resultant lack of blood flow to brain

• Heat exhaustion – mild form of shock with symptoms including extreme weakness or fatigue, uncoordinated action giddiness, nausea, headache and a weak rapid pulse

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Heat illness (continued)• Heat stroke – body’s thermoregulatory system has failed to

prevent core body temperatures rising to critical levels above 40°CSymptoms include: – lack of sweating and hot dry skin– confusion– irrational behavior– loss of consciousness– convulsions

Heat stroke may result in permanent damage to the brain and other vital organs; death may occur

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Factors leading to heat strain• Increase in core body temperature

• Lack of acclimatisation

• Lack of fitness and/or the presence of medical conditions

• Type and amount of clothing

• Dehydration

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Acclimatisation• Reduction in heat rate

• Reduction in core body temperature

• Increase in sweat rate

• Decrease in the electrolyte content of sweat

• Increase in blood plasma volume

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Risk factors for heat strain

Environmental risk factors• High temperature and/or humidity

• Reduced air movement

• Working near radiant heat sources

• Contact with conductive heat sources

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Individual risk factors• Age (especially greater than 60 years old)• Low level of physical fitness • Medical conditions (diabetes, cardiovascular disease) • Some medications • Drug and alcohol use• Lack of acclimatisation• Dehydration

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Workplace risk factors• High frequency, duration or intensity of physical activity• Requirement for use of personal protective equipment and

clothing (may increase humidity levels and prevent air flow across the skin)

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Indices of heat strain• Wet Bulb Globe Temperature

Index

• Thermal Work Limit

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Risk assessment and control

Heat stress guidance Australian Institute of Occupational Hygienists

Heat stress standard & documentation for use in the Australian environment

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Risk assessmentHeat stress risk assessments should consider:• individual characteristics• nature of the work• environmental conditions under which work is to be carried out

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Heat stress controls• Managing the risk of heat stress should consider the

hierarchy of controls (elimination, substitution, engineering, administration, personal protective clothing and equipment)

• Controls can be directed toward:– work environment– the task being carried out – individuals themselves

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Engineering controls• Ventilation – fans, blowers, chillers• Airconditioning – crib room, 4WD• Insulation or shielding – tents, shade

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Administrative controls• Training and education

• Employment assessment and monitoring

• Setting patterns of work

• Acclimatisation schedules

• Encouraging self pacing of work

• Maintenance of hydration

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Training• Ensure workers are fully aware of the underlying

mechanisms that allow heat strain to occur• Recognize the symptoms of heat illness• Understand and implement the correct responses to heat

stress conditions (including emergency first aid)

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Assessment and monitoring

• Medical surveillance may be required — determination of general fitness, presence of medical conditions and use of medications that may predispose employee to heat strain

• Persons at risk of heat stress can be monitored at workplace for signs of heat illness and to ensure work-rest and hydration regimes are followed

• Monitoring may also include assessment of:– recovery heart rate times– oral temperatures– end-of-shift weight loss (to determine level of dehydration)

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Work patterns• Shifts can be adjusted so that physical work occurs in

cooler periods of the day • Self pacing• Regular breaks and work-rest schedules• Provision of cool rest or recovery areas• Provision of relief workers

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Acclimatisation schedule• Un-acclimatised: 50% exposure on day 1, increasing

by 10% per day (i.e. full work regime by day 6)• Acclimatised but returning to work after more than 9

days off: 80% exposure on day 1; 90% on day 2 then full return to work

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Hydration• Goal is to restrict fluid loss to < 3%• Absorption rate through digestive tract about 1 litre/hour

(can lose up 1.5 litre/hour)• Encourage drinking cool fluids 250 ml every 15 minutes• Electrolyte replacement (especially non-acclimatised

workers)• Avoid caffeine, alcohol, milk, carbonated drinks, fruit juices

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Urine chart



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• PPE – cool vests


Review

• Thermoregulation• Heat gain, storage and loss• Heat strain and related illnesses• Risk factors for heat strain• Risk assessment and control

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Major points to consider

• Environment – temperature, humidity, wind speed

• Task – physical requirements, pace of work, clothing

• Acclimatisation – new to site or return to site

• Hydration – availability

• Individual – training, self regulation, buddy systems

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Government of Western Australia Department of Mines and Petroleum Please read this before using presentation This presentation is based on content presented.

Documents

radiant heat

petroleum heat strain

petroleum heat gain

loss heat strain

metabolic heat generation

heat strain risk assessment

inner core heat gain

work intensity heat