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 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 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 = Storage, which in the long term must equal 0 M = Metabolism W = External work done C = Convection R = Radiation K = Conduction E = Evaporation

Factors Influencing Heat Balance 1Work rate (i.e. activity or metabolic rate) Person 2Clothing 3Air temperatureEnvironment 4Radiant temperature 5Air Velocity 6Humidity (moisture) conditions

Metabolic Rate ActivityMetabolic Rate (W/m 2 body surface) Sleeping43 Resting47 Sitting60 Standing70 Slow Walk (2.5 kph)107 Walking (5 kph)154 Running ( 16 kph)600 Sprinting (25 kph)2370

Personal Insulation ClothingClo Value Naked0 Shorts0.1 Light summer clothes0.5 Typical indoor clothes1.0 Heavy suit1.5 Polar clothing3-4 Practical maximum5

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