BASIC PRINCIPLES IN OCCUPATIONAL HYGIENE Day 4 15

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BASIC PRINCIPLES IN OCCUPATIONAL HYGIENE Day 4

BASIC PRINCIPLES IN OCCUPATIONAL HYGIENE Day 4

15 - THERMAL ENVIROMENT

15 - THERMAL ENVIROMENT

Thermal Environment • In order to function effectively we need to maintain our bodies

Thermal Environment • In order to function effectively we need to maintain our bodies at a constant temperature within 36. 5 - 37. 5 o. C • 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

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

Heat Possible adverse effects of exposure to excessive heat include; • fatigue • behavioural

Heat 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

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. • Evidence regarding physiological acclimatisation to cold is conflicting

Cold Possible adverse effects to excessive cold include; • lassitude/listlessness • chilblains • frost

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

Psychological Responses to the Thermal Environment • People will often modify the way they work depending on 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 S=M+C+R–E Where M = C = R = E

Heat Transfer from the Body S=M+C+R–E Where M = C = R = E = S = Rate of metabolic heat production Convective heat loss or gain Radiant heat loss or gain Evaporative heat loss Heat gained or lost by the body Two more parameters, W (external work done) and K (conduction) are usually small and not considered so the simplified form is often used

Factors Influencing Heat Balance 1 Person 2 Work rate (i. e. activity or metabolic

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

Evaluating the Thermal Environment

Evaluating the Thermal Environment

Metabolic Rate Activity Sleeping Metabolic Rate (W/m 2 body surface) 43 Resting 47 Sitting

Metabolic Rate Activity Sleeping Metabolic Rate (W/m 2 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.

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 Environment • Duration of exposure – use work/rest tables to reduce risk of

Thermal Environment • Duration of exposure – use work/rest tables to reduce risk of prolonged exposure to heat Dry bulb temperature – dry sensor shielded from heat • – – • Simple thermometer - inexpensive, fragile, slow to respond Electrical thermometer – accurate, convenient Globe temperature – black copper globe with a simple thermometer in centre

Thermal Environment • Air velocity – heat removed from the body by convection when

Thermal Environment • Air velocity – heat removed from the body by convection when air current is passed over unless the air temperature is higher than the temperature of the skin. – – – Also affects evaporation of moisture from skin Vane anemometer - propeller type, directional, electrical or mechanical Resistance anemometer Kata thermometer Tracer smoke – visualise air flow and measuring low air velocities

Thermal Environment • Moisture Content – Convection and evaporation play a major role in

Thermal Environment • Moisture Content – Convection and evaporation play a major role in dissipating body heat and thus the temperature and moisture content of the air are important parameters – Natural wet bulb – simple thermometer with bulb covered and dipped in distilled water • Personal monitoring – heart rate and core temperature. If less than 30 minutes of work allowed or high levels of impervious PPE – undertake personal monitoring

Heat Stress Indices Various workers have devised indices to combine some of them into

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 – P 4 SR (Predicted Four Hour Sweat Rate): Calculated from charts and used to assess physiological limits

Heat Stress Indices • Thermal Work Limit (TWL): uses five environmental parameters plus clothing

Heat Stress Indices • Thermal Work Limit (TWL): uses five environmental parameters plus clothing factors to arrive at a prediction of a safe maximum continuously sustainable metabolic rate (Wm-2) for the conditions. Must be euhydrated and acclimatised • Predicted Heat Strain: adopted in ISO 7933. It describes a method for calculating the heat balance as well as the required sweat rate that the human body should produce to maintain this balnce in equilibrium.

Thermal Comfort • Very subjective and people will feel differently about what is the

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

Controlling the Thermal Environment

Controls Hot environments Cold Environment • • Reduce exposure to wind chill – wind

Controls Hot environments Cold Environment • • Reduce exposure to wind chill – wind barrier or refuge • Covering metal handles • Local heating • Use mechanical aids so sweat less • Workplace designed for use with gloves • Workplace designed so no prolonged sitting or standing • • Screen radiant heat Increase air movement Modify behavioural patterns Work/rest regimes Provide air-conditioned refuges Increase distance from local 'hot spots' Air cooling Protective clothing Provide readily accessible and palatable drinking water Allow time for employees to acclimatise after time-off

High Radiant Components • Surface temperatures surrounding a worker are hotter than the ambient

High Radiant Components • Surface temperatures surrounding a worker are hotter than the ambient air – Boiler rooms, engine and compressor house, power generating stations, inside military vehicles (tanks and aircraft) • Increase air velocity • Air conditioning/chillers • Cooled clothing • Shielding in smelting, furnace, steel making ad foundry where surfaces are extremely high

High Humidity Conditions • Laundries, mine, textile and other manufacturing processes, wet bulb and

High Humidity Conditions • Laundries, mine, textile and other manufacturing processes, wet bulb and dry bulb are both high (indicating high humidity) – Supply dehumidified air, projected into the area, increasing air velocity, improving comfort and reducing stress

Hot Dry Conditions • Deep dry mines, inside buildings (in tropics), and manufacturing where

Hot Dry Conditions • Deep dry mines, inside buildings (in tropics), and manufacturing where heat is emitted from plant – Increase air velocity – Cooled air