1. Topic 6 : Hazards of
Temperature Extremes
Topic Learning outcome :
1. Describe the definition of thermal comfort.
2. Explain the Heat stress and strain, and Cold stress condition.
3. Describe the identifying and assessing technique of hazard
temperature extreme.
4. Describe the temperature extreme control and prevention
strategies.

2. Introduction:
• Extreme temperatures, both cold and hot, have a significant effect on human
health and/or infrastructure- they can be dangerous.
• Humans are warm-blooded, that is, we have the physiological ability to
regulate our body’s internal temperature, which is kept at 37°C ± 2°C. If the
body’s core temperature either rises or falls beyond this, then serious illness
or even death may result.
• 6 factors that impact on a person to determine how they feel hot or cold;
Air temperature, humidity, radiant heat, Air movement, physical activity and
clothing.
• Also additional factors that effect individual ; Weight, health, level of fitness,
age, use of prescribed substances
• One all the influences on a individual are taken into account, that individual
will feel Thermal comfort, Thermal discomfort, Heat or Cold stress strain.
• In term of Health and Safety, heat and cold stress is a “significant hazard” and
heat and cold strain is “serious harm”.

3. Thermal Comfort:
• Thermal comfort is defined in British Standard BS EN ISO 7730
as: that condition of mind which expresses satisfaction with the thermal
environment.’
• So the term ‘thermal comfort’ describes a person’s psychological state
of mind and is usually referred to in terms of whether someone is
feeling too hot or too cold.
• Thermal comfort is difficult to define because need to take into account
a range of environmental and personal factors when deciding what will
make people feel comfortable.
• 6 factors affecting thermal comfort are both environmental and
personal.
Environmental factor :
Air temperature, Air velocity,
Radiant temperature,
Humidity.
Personal factor:
Metabolic heat, Clothing
Insulation

4. Thermal Comfort:
Why is thermal comfort important?
People working in uncomfortably hot and cold environments are more
likely to behave unsafely because their ability to make decisions and/or
perform manual tasks deteriorates.
For example; people may take short cuts to get out of cold environments, or
workers might not wear personal protective equipment properly in hot
environments increasing the risks, or
the workers' ability to concentrate on a given task may start to drop off and
increases the risk of errors occurring.

5. Thermal Comfort:
Calculating Thermal Comfort.
The predicted mean vote (PMV) and percentage people dissatisfied (PPD)
index and use of BS EN ISO 7730 and BS EN ISO 10551 British standards are
recommended.
The PMV/PPD index predicts the thermal comfort of people working in a
given environment.

6. Heat Stress and Strain:
Heat Stress Definition :
The net heat load on the body with contributions from both metabolic heat
production, and external environmental factors (i.e. temperature, relative
humidity, radiant heat transfer and air movement), as they are affected by
clothing.
There are THREE major forms of heat illness :
a) HEAT CRAMPS
- Muscle spasms which usually affect the arm, leg or stomach. Frequently
occur at night or when relaxing.
- Caused by heavy sweating, especially when water is replaced by drinking
but not salt or potassium.
b) HEAT EXHAUSTION
- Surface blood vessels and capillaries which originally enlarged to cool the
blood collapse from loss of body fluids and necessary minerals.
- This happens when we don't drink enough fluids to replace what were
sweating away.

7. Heat Stress and Strain:
HEAT EXHAUSTION
- The symptoms of heat exhaustion include: headache, heavy sweating,
intense thirst, dizziness, fatigue, loss of coordination, nausea, impaired
judgment, loss of appetite, hyperventilation, tingling in hands or feet, anxiety,
cool moist skin, weak and rapid pulse (120-200)
c) HEAT STROKE
- Is a life threatening illness with a high death rate.
- It occurs when the body has depleted its supply of water and salt, and the
victim's body temperature rises to deadly levels.
- A heat stroke victim may first suffer heat cramps and/or the heat
exhaustion before progressing into the heat stroke stage, but this is not
always the case.
- The early symptoms of heat stroke include a high body temperature ; a
distinct absence of sweating (usually); hot red or flushed dry skin; rapid
pulse; difficulty breathing; constricted pupils; any/all the signs or
symptoms of heat exhaustion

8. Heat Stress and Strain:
Heat Strain Definition :
Heat strain refers to the acute (short-term) or chronic (long-term)
consequences of exposure to environmental heat stress on a person’s
physical and mental states.
The physical effects of heat strain can vary from less serious disorders
such as skin rashes and fainting, to serious life-threatening situations
where sweating stops and heat stroke develops.
The following conditions are indications that heat strain is occurring:
- Dehydration
- Heat syncope (fainting)
- Heat rashes
- Heat cramps
- Heat exhaustion
- Heat stroke

9. Cold Stress:
Definition :
Cold stress is a response of the body to cold temperatures resulting from heat
loss from a portion of the body, such as the feet, hands, limbs or head.
Types of Heat Loss:
1) Radiation - heat is lost to the environment due to temperature gradient.
There is a difference in air temperature and body temperature.
2) Conduction- Heat loss through direct touch with a cold object. Heat loss is
the greatest when in direct contact with cold water.
3) Convection – Heat is lost from the body to the surrounding air as air moves
across a surface. This type of heat loss is dependent on air speed, with
increased wind speed there is greater heat lost.
4) Evaporation- Loss of heat due to water changing from liquid to gas. In the
human body is accomplished through sweating and breathing. Evaporation
of heat also causes the body to lose fluids, which can lead to dehydration.
Excessive exposure to cold can lead to hypothermia, which can be fatal.

10. Identifying and assessing hazards of
temperature extreme :
Hazard Identification
Step
Hot Environment
Identify hazard Heat is likely to be a hazard if, in addition to the work
process has :
• High radiant heat (e.g. from a dryer, an oven or
furnace)
• High humidity (e.g. kitchen or laundry)
• A high worker metabolic load.
• A person wearing clothing (such as PPE) that means
they cannot lose heat to the environment.
Assess hazards to
determine if they are
significant
Tools use to assess the heat hazard :
• Visual assessment
• Measuring the environment with a heat stress
monitor (wet bulb globe thermometer or WBGT)
• Direct physiological measurements e.g. body
temperature and heart rate.

11. Identifying and assessing hazards of
temperature extreme :
Hazard Identification
Step
Cold Environment
Identify hazard The following situation may present risk of cold stress :
• Situation where work outside in cold or wet
weather.
• Work and spend time in an artificially cold
environment e.g. walk-in fridge, cool store or
freezer
• Any person doing occupational diving
Assess hazards to
determine if they are
significant
• Measurement of temperature and wind speed as
well as observation of effects of cold on employees

12. Temperature extreme hazard control and
prevention strategies:
Hot Environment :
1) Environment controls :
• Provide ventilation to give significant air current. An increased air velocity
aids evaporation of sweat and cools the worker.
• Provide air conditioning either by reducing humidity or providing cooling.
• Shield the work environment from any radiant heat sources e.g. insulating
pipes.
2) Process Modification:
• Modify the process so that less heat is needed to carry out the task required.
• Reduce the heat created in carrying out a process to the lowest possible
level.

13. Temperature extreme hazard control and
prevention strategies:
Cold Environment :
1) Work environment:
• The cooling effects of air movement should be reduced by the provision of
effective shielding in the work area.
2) Equipment design:
• Metal handles and bars should be covered with thermal insulating materials.
3) Clothing:
• Protective clothing should be worn in all environments where work takes
place at temperature below 4oC.
• Hand protection need to be used when work at temperature below 16oC.
• Wear head covering as over 50% of heat loss is through the head.

14. Temperature extreme hazard control and
prevention strategies:
Cold Environment :
4) Safe work Practices; examples :
• Do not allow bare skin to come into contact with cold surface below -7oC.
• Do not allow bare skin to come into contact with evaporative liquids e.g.
petrol, cleaning fluids, alcohol.
• All work in cold conditions should be under constant observation (through a
buddy system or supervision).
• New employees should not be required to work full-time in the cold until
they have become accustomed to the working conditions.
• Apply lip balm and moisturizing lotions to prevent lesions.
• Maintain a high level of physical fitness.
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