Element B10 / 1 Thermal Comfort

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Eric Wilcox
5 years ago
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1 Thermal Comfort

2 Thermal Comfort HSE A person s state of mind in terms of whether they feel too hot or too cold If 80% employees comfortable employer reasonable

3 Thermal Comfort Not Just Temp Other environmental and personal factors to consider Environmental Air temp Radiant temp eg. From sun, fires, furnaces, molten metal Air velocity cooling effect on skin Humidity higher = feels warmer Personal Sweat slow to evaporate feels warmer Clothing Metabolic heat More physical activity more heat

4 Thermal Comfort Workplace (Health, Safety and Welfare) Regs 1992 Reg 7 Reasonable temperature in the workplace Reasonable number of thermometers Comfort ACoP reasonable comfort Where impracticable as close as possible to comfortable i.e. clear requirement to manage

5 Reasonable Temperature WHSWR ACoP At least 16 degrees 13 degrees for work which involves severe effort No Max But all reasonable steps should be taken through design of building Insulating hot pipes Air cooling plant Shading windows Locate workshops away from radiant heat Where no reasonable temp achieved Provide local cooling and heating Also protective clothing, rest facilities, SOW (task rotation)

6 Effects of High and Low Temperature Unit of heat Joule (J) Rate of heat emission J per sec = watt (W) 1kW = 1000w Body heat Normal range = 36.4 to 37.2 degrees

7 Effects of High and Low Temperature Heat transfer / heat loss Conduction Body in contact with sources Convection Heat transferred by current of moving air Radiation Radiant energy in the environment. Furnace etc. Evaporation Heat transferred to sweat

8 Effects of High and Low Temperature High Temperature Body temp regulated by rate skin radiates heat and evaporation Radiant process vasodilatation Skin temp raised sweating Excessive sweating muscle fatigue, cramps loss of salts Overheating heat stroke, coma, death.

9 Effects of High and Low Temperature Low Temperature Body cold blood vessels contract muscles under skin vibrate (shiver) to generate heat Extreme cold Frostbite Toes and fingers. Blood and oxygen diverted from extremities to vital organs Hypothermia Fall in body temp to below 35 degrees Severe below 30

10 Effects of High and Low Temperature Humidity High Limits body's ability to regulate heat through sweating Low Moisture taken from skin Dry cracked skin, lips Eyes and throat dry

11 Wet / Dry Bulb Air Temp Dry bulb Humidity Wet bulb

12 Air Temperature WHSWR Reg 7 Sufficient number of thermometers Does not show where temp coming from, only temp in vicinity Dry bulb thermometer most basic type Thermocouples very accurate measurements Personal Thermal Stress Monitor Audio and visual alarms if unsafe levels Tells worker to stop work immediately

13 Radiant Temperature Globe thermometer Suspended at point of measurement for at least 20 mins

14 Relative Humidity Hygrometers Psychrometer Wet and dry bulb. Both readings plotted onto psychrometric chart RH readings Whirling Hygrometer Wet and dry bulb side by side Rotated by hand Static Not accurate Forced Draught Hygrometer Extremely accurate As static but has fan, is insulated. Less susceptible to env effects

15 Metabolic Rate Rate calories are burned to maintain bodily functions Basal Metabolic Rate BMR Number of calories used by inactive person 60% calories used for normal body functions

16 Heat Balance Equation M = K +/- C +/- R +/- E +/- S Measures heat equilibrium in body Depends on Heat absorbed, heat evaporated, metabolic rate, calories used M = metabolic rate K = Heat exchange via conduction C = Heat exchange via convection R = radiation E = evaporation S = rate of heat storage (lost or gained) + = heat loss / - = heat gained. M always positive.

17 Heat Stress Indices Effective temperature Wet and dry bulb temp Combines temp, humidity and air movement Corrected Effective Temp As above but corrected for radiant heat Heat Stress Index Upper limits

18 Heat Stress Indices Predicted 4 hour sweat rate Environmental and personal factors Target below 2.7 litres in 4 hrs Not exceed 4.5 litres Wind Chill Index Work in low temp Air temp and velocity

19 Wet Bulb Globe Temp (WBGT) Quantify thermal stress Takes into account 4 main thermal factors affecting heat stress Humidity Air temp Air velocity WB (without whirling natural reading) DB Radiant heat GT Outdoor work WBGT = 0.7WB + 0.2GT + 0.1DB Indoor work WBGT = 0.7WB + 0.3GT

20 Wet Bulb Globe Temp (WBGT) Readings Compared against psychrometric chart Cross referenced with metabolic rate (work load) tables Defines safe working temperatures Continuous work Defined rest periods

21 Controls Control heat / cold source Screens, ventilation, insulation, Control environment Humidity, air movement, draughts Workplace design Insulate hot plant, air cooling, shaded windows, workshops away from heat, enclose product, pre-chill Job design Work rate, rotation, rest breaks, mechanical aids hot environments

22 Controls Clothing Suitable for temp, dress codes flexible Health surveillance Regular for those in extreme environments, also pregnant, ill, disabled, medicating. Monitor dehydration Training To recognise early symptoms of exposure to extreme temp

23 Controls Hydration Frequent cool drinks, small volumes Thirst not good indicator already too late

QUICK START GUIDE. QUESTemp o 32 Heat Stress Monitors

QUICK START GUIDE. QUESTemp o 32 Heat Stress Monitors QUICK START GUIDE QUESTemp o 32 Heat Stress Monitors Up and running 1. Make sure the wet bulb wick is clean. Fill reservoir with distilled water. + Check and fill wet bulb reservoir: remove the reservoir