Element B10 / 1

Element B10 / 1

Thermal Comfort

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

Element B10 / 1

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

Sweat slow to evaporate – feels warmer

Personal

Clothing

Metabolic heat

More physical activity – more heat

Element B10 / 1

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

Element B10 / 1

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)

Element B10 / 1

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

Element B10 / 1

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

Element B10 / 1

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.

Element B10 / 1

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

Element B10 / 1

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

Element B10 / 1

Wet / Dry Bulb

Air Temp

Dry bulb

Humidity

Wet bulb

Element B10 / 1

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

Element B10 / 1

Radiant Temperature

Globe thermometer

Suspended at point of measurement for at least 20

mins

Element B10 / 1

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

Element B10 / 1

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

Element B10 / 1

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.

Element B10 / 1

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

Element B10 / 1

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

Element B10 / 1

Wet Bulb Globe Temp (WBGT)

Quantify thermal stress

Takes into account 4 main thermal factors affecting

heat stress

Humidity WB (without whirling – natural reading)

Air temp DB

Air velocity

Radiant heat GT

Outdoor work

WBGT = 0.7WB + 0.2GT + 0.1DB

Indoor work

WBGT = 0.7WB + 0.3GT

Element B10 / 1

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

Element B10 / 1

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

Element B10 / 1

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

Element B10 / 1

Controls

Hydration

Frequent cool drinks, small volumes

Thirst not good indicator – already too late

Element B10 / 1