Heat resistant

to identify the rationale with which to support the frequency and type of
health monitoring of employees, in relation to heat exposure in their working

has long been known that working in the heat can compromise health and safety
and lead directly or indirectly to worker injury and death.1

aim of this article is to identify the frequency, type and rationale behind the
proposals for the monitoring of employees exposed to heat, rather than, as is
currently the case, the sole focus being based on risk attached to individuals’
working roles.

current occupational hygienic limit values for heat stress are based on acute
reactions to heat stress rather than to the effects of chronic heat exposure.

objective is to encourage an active, specialist and operational
multidisciplinary team to formalise safer systems of work and to identify
research opportunities that employers could pursue to provide a benchmark for
standardised practice. This should be addressed from the organisational, macro
and micro working climate, for it to be successful.2


exposure is a risk involved in many job roles and in relation to the
surrounding environment, such as for outdoor workers/labourers, miners, foundry
workers, armed services personnel and front-line public sector emergency
services. This is mainly due to the increased use of personal protective
equipment (PPE); for example firefighters’ uniforms, police officers’
stab-proof vests and ambulance crews’ overalls, all worn to protect employees
from personal harm; whether weapons, flame; biological or chemical spillage.

body can maintain its core temperature between 36.5ûC and 37.5ûC. Heat is
produced by the body’s muscular activity, metabolic reactions and endocrine
activities, and is removed by the mechanisms of convection, conduction,
radiation and evaporation. Problems occur when this core temperature rises due
to the external environmental temperature or over-exertion. When the ‘removal
systems’ fail and the body’s temperature rises above 40ûC, it can cause
irreversible damage to the body’s organs.3,4

heat exposure

rise in heat exposure causes the following signs and symptoms, in varying
degrees, depending on the individuals’ health, working role, the PPE worn, type
and duration of exposure:

Irritability, discomfort

Lowered work performance

Heat rash

Heat cramp

Heat exhaustion

Heat stroke

Heat syncope (sudden dizziness)

Heat tetany (muscle spasms, respiratory problems)

Heat oedema (swelling due to fluid build-up)


Heat cataracts.3,5,6

stroke is a medical emergency and, according to Williams, it is most common in
those who are un-acclimatised, obese, dehydrated, inappropriately dressed and
who have consumed alcohol.3

organ systems are affected:

The brain

Haemostatic system (blood clotting control mechanism)





the Army’s defence council instructions on the prevention and treatment of heat
illness, it identified that heat exhaustion and heat stroke should be seen as a
heat illness, meaning that individuals become incapacitated as a result of a
rise in body temperature.5 This is because it can often be difficult to
determine the difference between the signs and symptoms of heat exhaustion and
heat stroke, and an incorrect diagnosis may lead to a poorer outcome for the
heat-exposed individual. Susceptibility varies widely in terms of:

Temperature duration threshold at which the injury occurs

The systems affected

Severity of which a given system is affected

Duration of the latent period following heat exposure before an injury

short, there is no elevated temperature-duration threshold below which heat
injury will never occur, and all cases of heat illness should be admitted
promptly to hospital for observation for at least 24 hours.7

order to determine the type, frequency and requirement for medical screening to
be carried out, research needs to be undertaken to identify the long-term
effects of heat exposure in specific work roles.

heat exposure

has been very little research into chronic heat exposure, except for research
involving small animals.8, 9,11,12

couple of studies that identified human reactions to heat included a study by
Hobbesland, Kjuus and Thelle, who investigated the increased mortality from
sudden death in 12 Norwegian ferro-alloy plant workers. Hypertension-related
diseases were found to be associated with the common furnace work conditions
(heat, psychosocial stress, shift-work, noise and carbon monoxide), found in
many industrial settings.13

et al attempted to identify the initial human body adaptation to chronic
passive heat exposure using a series of nocturnal blood collections.14

collections monitored growth hormones, prolactin, thyrotropin and plasma renin
activity from 12 males over 11 days in a heat controlled climate. It was noted
that after five days, those exposed to a higher temperature had stimulated
plasma renin activity, but this had little affect on pituitary hormones. Those
kept at a steady lower temperature of 32ûC throughout the tests experienced no
change in hormone profiles.

conclusion was that the main endocrine system involved in acclimatisation to
passive heat exposure is the renin angiotensin system, due to its counteractive
processing against salt and water loss.

from the physiological reaction to heat in humans, other considerations need to
be addressed which can disturb the body’s natural heat balance.13,14


Excessive physical exertion

Hot weather and high humidity

Inadequate fluid intake/hydration level

Infections and medical conditions

Wearing heavy dark clothing on hot days/clothing which inhibits adequate heat

Extremes of age/older workers

Inappropriate environments, such as unventilated, tin-roof factories

Lack of acclimatisation

Low blood sugar/lack of food

Direct external environment/summer weather

Recent alcohol consumption

Obesity. 3,15,16,17

consideration should be that some medications can impair heat loss, including:

Cardiac drugs

Oral hypoglycaemics





Neuroleptics (chlorpromazine)





Cocaine. 18


stress in workplaces should be considered at an individual, organisational and
macro level. 16

risk at an individual level can be difficult to determine, due to differing
organisational demands, occupational status, individual health, shift patterns,
and workload. On a macro level, there is an effect on economic climate to
workplace objectives, community provision, service procurement and service

individual may be seen as being at greater risk where there is less routine
heat exposure, causing a reduced ability to acclimatise to the working role.
Acclimatisation can take between three to 14 days depending on the health,
gender and overall fitness of the individual adapting to the heat.18

of the worker is very important in this situation as they need to know that
they are placing increased demands on their bodies after a holiday, long
weekend or period of illness.3,19

Army has been at the forefront of risk management with heat exposure and uses
the standard index of the Wet Bulb Globe Temperature (WBGT) as a guide for its
own workers. It uses an acclimatisation regimen to prevent heat stress, whereby,
for a soldier to be acclimatised, he/she should have taken regular exercise for
longer than 10 days in the same environment as the proposed activity.5,6

should take place with the workforce, according to their perception of the most
demanding aspect of their job,19 and specialists should set the maximal
permissible limits for work duration. This is because it has been identified
that the actual heat strain experienced by workers does not necessarily
correlate with the current ISO 7933 standards for heat stress.1,20 The risk
assessment should take into account the working conditions, job demands and
current in-house workplace policies, and national legislative standards.1,2

and Gravelling, in their research in UK coal mines, identified a potential
problem where high temperatures and humidity levels were ‘the norm’.21 One
solution to this was their production of a code of practice to reduce the
miners’ physiological symptoms of heat stress, as it was noted that as well as
increasing the amount of fluids available in relation to their sweat loss, the
miners core temperatures increased with basic effective temperatures.

was concluded that action should be taken to reduce the risk of heat strain
where their basic effective temperatures were routinely more than 27ûC.20

simple approach can be adopted in the workplace, based on education on
hydration, provision of readily available water fountains/fluid containers and
a canteen with water-rich foods, such as mousses and yoghurts, which can
contribute 1,000ml towards daily fluid intake, including approximately 300ml
generated through the metabolism of dietary protein, fat and carbohydrate.21

further, more complex individual risk assessment is presented by Malley, who
advises a prescriptive weight/fluid balance maintenance system for
firefighters, whereby they pass water in the morning at the beginning of a day
shift, then weigh him/herself and re-hydrate as necessary. For each pound (lb)
of water weight lost, there should be a replacement of 16 fluid ounces of

is the key, according to Pribut, who advised that hydration should occur up to
45 minutes prior to exercise in a hot environment, with a cupful of water
consumed every 10 to 15 minutes.16

exercise from between 60 to 90 minutes in duration, sport replacement drinks
should be used post-exercise, because the electrolytes and carbohydrates they
contain assists the individuals in their recovery period.

Professor World identified that many sports drinks contain added salt and he
identifies that salt intake in food is normally adequate to meet the body’s

practitioners must therefore be mindful of each individual’s pre-existing
medical conditions when advising on the content of re-hydration fluids.

reviews of healthcare maintenance and detection of illness through health
screening have increased the likelihood of detecting workers’ underlying
medical conditions earlier.

conditions such as diabetes, hypertension, heart disease, anorexia nervosa,
bulimea, obesity, alcoholism and fever may cause an enhanced reaction to heat
stress.3,18 And some medications can further impair the body’s ability to
tolerate heat and adapt to hot environments. The patient may become too
dehydrated to sweat and the core body temperature will rise leading to heat

could produce a procedural note to accompany the risk assessment as part of an
education package, identifying how a recovery rate from exposure to hot
environments can be assisted before, during and after a working day. This
should have identified the structure and diversity of the workforce, including
the age, cultures and genders, (as women tend to be less tolerant to heat
exposure due to their different physiological make-up), but is not related to
fitness to undertake the work role.6

charts provide simple education material and assist the worker in undertaking
an individual daily risk assessment system. Most authors indicate that
re-hydration should take place on a regular basis throughout the heat exposure
in the working day, with the following issues addressed:

Drink cool, not cold fluids, try to avoid hot fluids

Make sure diluted beverages contain less than 8 per cent glucose

Continue to drink six to eight fluid ounces of water every 10 to 15

possible, those workers who have to work in emergency situations, wearing PPE,
should be allowed to adopt a procedure in which they:

Re-hydrate away from the hot environment

Do not consume solid food immediately post-incident

Do not continue working at a relatively high exertion level (exceeding 75 per
cent of maximum aerobic ability). 17,19,23,24,25

high temperatures individuals work in causes heart rates to increase. Core
temperatures increase approximately 1ûC when wearing PPE, which further
increases by 0.5ûC in the recovery period on completion of the task. If PPE is
not removed at this point, there is a greater risk of heat exhaustion than at
the start of a rest period.

policies should acknowledge the need for formal education of workers, the
benefits and limitations of PPE and a recovery period and safe environment away
from the heat and therefore danger, to reduce the accumulation of physiological
strain, in which to remove protective clothing.3,26,27,28,29

six measurements are critical when identifying heat stress risk:

Air temperature

Radiant temperature

Air velocity


Clothing properties

Metabolic rate.1

dynamic risk assessment on each individual would be advantageous prior to
working in heat, and also for those returning to heat exposed work, especially
for new workers, keen to prove their work capability, who may inadvertently
increase their susceptibility to cardiovascular and psychological strain in
heat if they continue to work.30


a test research programme (as advised by Professor World), using the
Cockcroft-Gault equation to establish any relation to the long-term effects of
heat exposure. Allow OH practitioners to continue to define the risk afforded
to their employees and therefore establish the frequency and type of medicals
to be undertaken.

longitudinal study could involve using a set of similar individuals in relation
to their work role in the same occupation, in relation to the amount of
historical working life, heat exposure, for example, those with regular heat
exposure – at least twice per week on a regular basis and the other group with
intermittent exposure.

pairing would be divided according to the following criteria, as near as
possible, in relation to:





General smoking habits

Alcohol consumption

Length of service in working role

Blood pressure readings

Number of heat exposures

Professional records (of heat exposure rather than personal recollection).

tests would be taken for urea and electrolytes in addition to an electro
-cardiogram for the potential relationship with the chronic effects of heat
exposure on the circulatory system, to determine the effect of the exposure on
the body systems.

conclusion, industries in which the workforce is at a level of risk due to
heat-induced illness should provide care from an organisational, macro and
micro level. Further research is required to determine the exact requirement
for monitoring of workers who are exposed to heat in their workplace and who
have additional risk factors, which can disrupt the body’s natural heat
balance. Above all, personal initiative, experience, assessment or advice from
all team members should all contribute to the decision.32

Lindsey Wood BA (Hons) Humanities, OHND, RGN

thanks to: Lt.Col. M World, professor of military medicine, Queen Elizabeth
Hospital, Renal Unit; Phil Castleton, West Midlands Fire and Rescue Service;
Andy Tait, Leicestershire Fire and Rescue Service; Steve Rose, of the Dyslexia
Advice Resource Centre; Paul Fernley, occupational health nurse; and Dr Philip
Hamilton, Fire Brigade medical adviser

Recommendations for employers

– Develop a strategy/policy/procedure and code of practice
in the workplace, which involves scope (nature of work role, use of PPE and
equipment), validity (does the method relate to the strain on the individual
worker) and easy application in the workplace (not too complicated and
appropriate to their workplace)1

– Assess heat strain to determine the maximum allowable
exposure duration in relation to tolerance time. Sweat rate, evaporation
efficiency, water loss; increase in core temperature, work rate, rest
interface, range of duties, use of combinations of clothing and surrounding

– Provide training by OH practitioners explaining the signs
and symptoms of heat induced illnesses

– Active education and presentation materials on hydration
and nutrition on how to plan for the day. Provision of water containers for
carriage and storage at work/in vehicles as necessary

– Use of hydration charts for individual hydration status

– Monitoring and use of heat exposure records

– Post heat exposure checklist

– Fitness programme (according to age)

– Validate present form of PPE and raise awareness of the
limitations of PPE

– Investigate and research innovations in PPE wear, such as
an ice, freon, water or air-cooled vests 27, 31

– Use a virtual-reality computer-based training programme
for practice, to avoid heat exposure in real-life training scenarios

– On site health surveillance every six months, for the
first year, by an OH practitioner, with further frequency determined by the
initial test results, to include:

– Health questionnaire (based on a healthy lifestyle

– Blood pressure

– Cholesterol test (for those at a greater risk of
cardiovascular disease)

– Weight

– Urine analysis for proteinuria, haematuria, specific
gravity (SG) results (to monitor the concentration and diluting power of the
kidneys and also recognising any dehydration), to be used as an additional
education tool31

– Review of time sheet/heat exposure

– Medical for the over-40s

– Assessment of general health and medication side-effects.


1. Parsons and Bethea (2002). The Development of a
Practical Heat Stress Assessment Methodology for use in UK Industry. Prepared
by Loughborough University for the HSE. Research report 008.

2. Whittaker S C (2001). The Management of Sickness
Absence. 420-424. www.occenvmed.com

3. Williams N (1993). Working in a Hot Environment.
Occupational Health. August. 275-277.

4. Edwards C, Bouchier I, Haslett C and Chilvers E. (1995)
Davidsons Principles and Practice of Medicine. London: Churchill Livingstone.

5. Harrington J M and Gill F S (1998). Occupational Health.
ISBN 0-632-04832-8.

6. Defence Council Instructions. Joint Service. Ministry of
Defence. (1996) Heat Illness in the Armed Forces: Prevention and Treatment.
(59): 1-11.

7. Lt. Col. World M J, (1995). Policy for treatment of the
Adverse Effects of Heat in Military Patients 1-3.

8. Dukes – Dobas, F N. (1981). Hazards of Heat Exposure. A
Review. Scandinavian Journal of Work and Environmental Health. (2): 73-83.

9. Tohoku J. (1998) Effects of mild chronic heat exposure
on the concentrations of thiobarbituric acid reactive substances, glutathione,
and selenium, and glutathione peroxidase activity in the mouse liver. Exp. Med,
185 (2): 79-87.

10. Temim S, Chagneau A M, Peresson R, Tesseraud S. (2000)
Chronic Heat exposure alters protein turnover of three different skeletal
muscles in finishing broiler chickens fed 20 per cent or 25 per cent protein
diets. Journal of Nutrition. 130 (4): 813-819.

11. Geraert P A, Padilha, J C, Guillaumin S. (1996).
Metabolic and Endocrine changes Induced by Chronic Heat Exposure in Broiler
Chickens: Biological and Endocrinological Variables. British Journal of
Nutrition. 75 (2): 205-216.

12. Samuels S E, McAllister T A, Thompson J  R (2000). Skeletal and Heart Muscle Protein
Turnover during Long Term Exposure to High Environmental Temperatures in Young
Rats.  Canadian Journal of Physiological
Pharmacology. 78 (7): 557-564.

13. Hobbesland A, Kjuus H and Thelle D S (1997). Mortality
from Cardiovascular Diseases and Sudden Death in Ferro-alloy Plants.
Scandinavian Journal of Work, Environment and Health. 23 (5): 334-341

14. Saini J, Brandenberger G, Libert J P, Frollenius M
(1993). Nocturnal Pituitary Hormone and Renin Profiles during Chronic Heat
Exposure. Journal of Applied Physiology. 75 (1): 294-300.

15. Extremes of Temperature. Hypothermia and Heat Induced
Illness (Hyperthermia) (2002) www.members.ozemail.co.au/tarong/extremes.htm

16. Priburt S M, Dr. (2002). Running in the Heat: 2000
Version. Dr Stephen M Priburt’s Sports Pages. (www.drpribut.com/sports)

17. Shade B R (1996). Heat Injuries. Emergency. 18-24.

18. Micromedex Inc, 1999. Drug Induced Hyperpyrexia and
Heat Stroke. Vol. 100. Exp. 30 June 1999. (From West Midlands Drug Information
Service, Good Hope Hospital, Sutton Coldfield)

19. Faff J and Tutak T (1989). Physiological Responses to
Working with Fire Fighting Equipment in the Heat in relation to Subjective
Fatigue. Ergonomics. (32) 6: 629-638.

20. Stirling, M, Leicestershire Fire and Rescue Service

21. Hanson M A (1999). Physiological Monitoring of Heat
Stress in UK Coal Mines. Institute of Occupational Medicine. Edinburgh. HSE Abstracts

22. Thirsty Work. Information for Medical Professionals. 4-6

23. Malley K S (1995) Heat Stress: Part 2. Maximum
Hydration. Firehouse. 112-113.

24. Smith D L, Manning, T S, Petruzzello S J (2001). Effect
of Strenuous Live Fire Drills on Cardiovascular and Psychological Responses of
Recruit Firefighters. 44 (3):  244-254.

25. Orfinger B (2002). Disaster Relief.org. Scientist
Studies Health Risks for Firefighters at Ground Zero and Elsewhere. 17

26.  US Department
of Labour. (2002) Occupational Health and Safety Administration. Heat Stress.
(Heat Stress Card) OSHA Technical Website. Section III: Chapter 4.  (www.osha-slc.gov.)

27. Lusa S, Louhevaara V, Smolander J, Pohjonen T, Uusimaki

and Korhoned O (1993). Thermal effects of Fire – Protective
Equipment during Job Related Exercise Protocol. Safe Journal. (23) 1: 36-39.

28. Carter J B, Banister E W and Morrison J B (1997). The
Effectiveness of Rest Conditions in the Prevention of Heat Stress. Fire
Engineering. 67-70.

29. Clark, D L, Dr, Smith D F and Denise L (1998). Heat
Stress in the Training Environment. Fire Engineering. 151 (3) 163-164.

30. Yakin, Heather, 1999. Firefighters wonder if gear is
safe. The Times Herald-Record. 28 September. 1-3.

31.  Bayer
Diagnostics. Urine Analysis. The Essential Information. Bayer plc. Berkshire.

32.  Home Office. HM
Fire Services Inspectorate. Chief Officers Letter. 2000. DCOL. 6 April. London.

Learning for life
CPD Heat stress

1. At present, occupational hygiene limits for heat stress are based on?

a) Acute reactions
b) Chronic reactions
c) Long-term exposure
d) The temperature

2. The body’s core temperature should be maintained at between:

a) 35-38C
b) 30 -40C
c) 36-38C
d) 36.5-37.5C

3. Heat is removed from the body by:

a) Evaporation, emission, convection
b) Convection, conduction, emission
c) Convection, conduction, evaporation
d) Evaporation, conduction, emission

4. All cases of heat stress should be admitted to hospital for at least:

a) 24 hours
b) 12 hours
c) 1 week
d) 5 days

5. Research carried out by Saini et al showed that those exposed to high
temperatures for five days had what sort of effect on the pituitary hormones?

a) Little effect
b) No effect
c) A marked effect
d) A rise in

6. Which of the following medications was NOT listed as improving heat

a) Diuretics
b) Barbiturates
c) HRT
d) Antidepressants

7. Acclimatisation can take:

a) 1-2 days
b) 3-14 days
c) 14-21 days
d) 6 weeks

8. What factors affect acclimatisation?

a) Age, gender, fitness
b) Health, gender, fitness
c) Health, age, gender
d) Age, health, fitness

9. The standard index WBGT stands for:

a) Washed bulb globe temperature
b) Wet bulb gulf thermometer
c) Wet bulb globe thermometer
d) Wet bulb globe temperature

10. Pribut advises that for pre-hydration before exercise in a hot
environment, a cupful of water should be consumed:

a) One hour before
b) 20-30 mins before
c) Every 10-15 minutes for 45 minutes before
d) 30-40 minutes before

Answers & Feedback

1) a – If you got this answer wrong, you must really go back and revise your
knowledge of the body’s temperature control mechanisms.

2) d

3. c – this is basic physics – so maybe hunt out your GCSE books or do a bit
of revising! It is important to understand what each one means.

4) a

5) a – It may be worth revising your knowledge of pituitary hormones or
getting a copy of this research.

6) c – However, it does help to control hot flushes!

7) b – This answer is a debatable and it may be worth reading some other
research on this topic, but it certainly explains why when you are just getting
used to the hot weather on holiday, it’s time to come home!

8) b

9) d – See the Resources page to find out where you get more information
about this important index.

10) c – This fact is well worth knowing for those of you planning on doing
lots of physical activity this summer.

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