BASIC PRINCIPLES IN OCCUPATIONAL HYGIENE Day 4. 15 - THERMAL ENVIROMENT.
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Transcript of BASIC PRINCIPLES IN OCCUPATIONAL HYGIENE Day 4. 15 - THERMAL ENVIROMENT.
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BASIC PRINCIPLES IN OCCUPATIONAL HYGIENE
Day 4
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15 - THERMAL ENVIROMENT
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THERMAL ENVIROMENT
• In order to function effectively we need to maintain our bodies at a
constant temperature within 36.5 - 37.5 oC.
• Temperature regulation centres in our brain are sensitive to small
changes of blood temperature and also get feed back from
sensory nerves at the skin.
• Our brains then use this information to adjust our bodies
responses to heat.
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HEAT
Physiological responses to heat– Blood vessels in skin expand– Pulse rate increases. – Increases blood to the surface of the body.– Sweating also increases heat loss due to latent heat of evaporation. – In very hot conditions, sweating offers greatest potential for regulating
body temperature.
Possible adverse effects of exposure to excessive heat include; – fatigue, – behavioural modification,– reduced concentration, – heat cramps due to salt loss, – fainting heat exhaustion – heat stroke.
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COLD
Physiological responses to cold– Blood vessels in skin contract – Heat flow to the body surface is reduced– Heat production is increased by physical activity and
shivering. – No physiological acclimatisation to cold.
Possible adverse effects to excessive cold include; – lassitude/listlessness, – chilblains, – frost bite – hypothermia.
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Psychological Responses to the Thermal Environment
• People will often modify the way they work depending on the thermal environment.
• Modify their local work environment
– moving to a more comfortable area,
– changing clothes,
– increasing or decreasing ventilation
• Performance and efficiency can also be affected by adverse thermal conditions.
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Heat Transfer from the BodySix parameters that may be taken into account:
S = M ‑ W + C + R + K ‑ E
Where: S = Storage, which in the long term must equal 0M = MetabolismW = External work doneC = ConvectionR = RadiationK = ConductionE = Evaporation
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Factors Influencing Heat Balance
1 Work rate (i.e. activity or metabolic rate)
Person
2 Clothing
3 Air temperature Environment
4 Radiant temperature
5 Air Velocity
6 Humidity (moisture) conditions
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Metabolic RateActivity Metabolic Rate
(W/m2 body surface)
Sleeping 43
Resting 47
Sitting 60
Standing 70
Slow Walk (2.5 kph) 107
Walking (5 kph) 154
Running ( 16 kph) 600
Sprinting (25 kph) 2370
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Personal Insulation
Clothing Clo Value
Naked 0
Shorts 0.1
Light summer clothes 0.5
Typical indoor clothes 1.0
Heavy suit 1.5
Polar clothing 3-4
Practical maximum 5
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THERMAL ENVIROMENT
• Dry Bulb Temperature
• Mean Radiant Temperature
• Air Velocity
• Personal monitoring.
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Heat Stress IndicesVarious workers have devised indices to combine some of them into a single figure to which a standard could be applied. Some of these include:
– Wet Bulb Globe Temperature: A simple index calculated after measuring the dry bulb, natural wet bulb and globe temperatures.
– HSI (Heat Stress Index): Calculated using a range of environmental measurements as well as work rate.
– P4SR (Predicted Four Hour Sweat Rate): Calculated from charts and used to assess physiological limits.
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Thermal Comfort
• Very subjective and people will feel differently about what is the ‘ideal’ thermal environment.
• Much less extreme conditions than thermal stress.
• Indices have also been generated in an attempt to measure thermal comfort.
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Controlling the Thermal Environment
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Specific Environmental Problems
High radiant components
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Specific Environmental Problems
High humidity conditions
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Specific Environmental ProblemsHot dry conditions