MEASURING HEAT STRESS – Measuring the person

When the worker is under heat stress, body temperature will rise. The body reacts by using its various mechanisms to keep the body temperature as constant as possible. The skin temperature will rise (the heart beat will increase, breathing will normally be deeper; and the worker will perspire. Thus the body temperature (core temperature measured in the mouth) will show the result of all these protective mechanisms. However the body temperature should not change by more than about 1⁰C.

For most levels of heat stress found in industry, the rate of perspiration indicates the strain produced on the body. The amount of perspiration in a working period can be measured by calculating the loss of body weight discounting the weight taken in by eating and drinking, weight lost when going to the lavatory, and any changes in weight of clothing. This can be up to a few kilogrammes after a day’s work in hot environment.

Perspiration contains salt. If there is a lot of perspiration, the body loses a lot of salt. In extreme cases, cramp occurs in muscles due to a shortage of salt in the body.

The water and the salt lost by perspiration must be replaced. Unfortunately it is not enough just to drink when you feel thirsty. A fit young person in a very hot zone can lose more than one litre of perspiration in an one hour. But normally he can tolerate losing up to about 4 litres in an 8-hour shift provided he replaces the water and the salt. The replacement should be by drinking either pure water or by drinking fruit juices. Adding salt to food and eating foods that contain natural salt and other minerals will also be helpful.

Anyone not taking in enough water to replace perspiration loss will not pass very much urine; that which does pass will be strong and darker in colour. This is unhealthy.

Perspiration is essential. The body will never perspire unnecessarily. It is dangerous to try to reduce perspiration by drinking less.

Two medical effects of heat are heat exhaustion and heat stroke:

• Heat exhaustion is when you feel dizzy and faint and is due to a shortage of blood to the brain. Blood pressure falls. Lie down in a cool place so that the blood can flow to the head;
• Heat stroke is when the workers skin is very hot and dry and is due to the perspiration mechanism not working properly. There is a rapid rise of body temperature to over 40⁰C, a medical emergency and medical assistance must be summoned immediately. While waiting it is vital to cool the body by sponging.

Acclimatization occurs when a person lives and works in hot climate. It means that the person has adjusted and adapted to the hot climate. For fully acclimatized people, body temperature and the heart rate react less to working in heat. They perspire easily and perspiration is less salty. They can also have greater blood circulation near the skin.

There is, however, a limit to how much the body can adapt. Even for the fully acclimatized person heat stress should be reduced as much as possible.