Transcript BASIC PRINCIPLES IN OCCUPATIONAL HYGIENE

BASIC PRINCIPLES IN
OCCUPATIONAL HYGIENE
Day 4
15 - THERMAL ENVIROMENT
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.
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.
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.
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.
Heat Transfer from the Body
Six parameters that may be taken into account:
S=M-W+C+R+K-E
Where: S
M
W
C
R
K
E
=
=
=
=
=
=
=
Storage, which in the long term must equal 0
Metabolism
External work done
Convection
Radiation
Conduction
Evaporation
Factors Influencing Heat Balance
1
Person
2
Work rate (i.e. activity or
metabolic rate)
Clothing
3
Air temperature
Environment
4
Radiant temperature
5
Air Velocity
6
Humidity (moisture)
conditions
Metabolic Rate
Activity
Sleeping
Metabolic Rate
(W/m2 body surface)
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
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
THERMAL ENVIROMENT
•
Dry Bulb Temperature
•
Mean Radiant Temperature
•
Air Velocity
•
Personal monitoring.
Heat Stress Indices
Various 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.
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.
Controlling the Thermal Environment
Specific Environmental Problems
High radiant components
Specific Environmental Problems
High humidity conditions
Specific Environmental Problems
Hot dry conditions