Heat Stress

by Dru Sahai, M.Sc. (A), Project Coordinator, CSAO

 

Where does heat stress occur in construction?

Heat stress can occur wherever construction operations involve heavy physical work in hot, humid environments. The locations may be indoors (mills, foundries, electrical vaults, interior renovation, etc.) or outdoors (road-building, excavation, roofing, home-building, etc.).

Asbestos removal and other operations that require workers to wear semi-permeable or impermeable protective clothing can contribute significantly to heat stress. Heat stress causes the body's core temperature to rise.

What happens when the body's core temperature rises?

The human body functions best within a narrow range of internal temperature. This core temperature varies from 36°C to 38°C. A construction worker performing heavy work in a hot environment builds up body heat. To get rid of excess heat, the body uses two cooling mechanisms:

1) The heart rate increases to move blood -- and heat -- from heart, lungs, and other vital organs to the skin.

2) Sweating increases so that more sweat can evaporate and cool the body.

Sweating is the body's most important way of dispersing excess heat. But when too much sweat is lost through heavy labour or working under hot, humid conditions, the body doesn't have enough water left to cool itself. The result is dehydration. Core temperature rises above 38°C. A series of heat-related illnesses, or heat stress disorders, can then develop.

How can we recognize heat stress disorders?

Heat stress disorders range from discomfort and pain (heat rash and heat cramps) to life-threatening conditions (heat exhaustion and heat stroke).

Heat exhaustion occurs when the body can no longer keep blood flowing to supply vital organs and at the same time send blood to the skin to reduce body temperature. Signs of heat exhaustion include

• weakness
• difficulty continuing work
• headache
• breathlessness
• nausea or vomiting
• feeling faint or actually fainting.

Workers fainting from heat exhaustion while operating equipment can injure themselves and others. Heat exhaustion casualties respond quickly to prompt first aid. Cooling off is the objective. Have the casualty

• rest in a cool place
• drink cool water
• remove unnecessary clothing
• loosen clothing
• shower or sponge with cool water.

It takes 30 minutes at least to cool the body down once a worker suffers heat exhaustion. If not treated promptly, heat exhaustion can lead to heat stroke -- a medical emergency.

Heat stroke occurs when the body can no longer cool itself and body temperature rises to critical levels. Signs include

• confusion
• irrational behaviour
• loss of consciousness
• convulsions
• lack of sweating
• hot, dry skin
• abnormally high body temperature -- for example, 41°C.

Heat stroke requires immediate medical attention.

• Call 911 or your local emergency number.
• Provide immediate, aggressive, general cooling.
• Immerse casualty in tub of cool water, place casualty in cool shower, or spray casualty with cool water from a hose.
• Wrap casualty in cool, wet sheets and fan rapidly.
• Transport casualty to hospital.
• Do not give anything by mouth to an unconscious casualty.

Do personal factors increase the risk of heat stress?

Certain physical conditions can reduce the body's natural ability to withstand high temperatures:

Weight
Workers who are overweight are less efficient at losing heat.

Poor physical condition
Being physically fit aids your ability to cope with the increased demands that heat puts on your body.

Previous heat illnesses
Workers are more sensitive to heat if they have experienced a previous heat-related illness.

Age
As the body ages, its sweat glands become less efficient. Workers over the age of 40 may have trouble with hot environments. Acclimatization to heat and physical fitness can offset some age-related problems.

Heart disease or high blood pressure
In order to pump blood to the skin and cool the body, the heart rate increases. This can stress the heart.

Recent illness
Workers with recent illnesses involving diarrhea, vomiting, or fever have an increased risk of dehydration and heat stress because their bodies have lost salt and water.

Alcohol consumption
Alcohol consumption during the previous 24 hours leads to dehydration and increased risk of heat stress.

Medication
Certain drugs may cause heat intolerance by reducing sweating or increasing urination. Workers in hot environments should consult their physician or pharmacist before taking medications.

Lack of acclimatization
When exposed to heat for a few days, the body will adapt and become more efficient in dealing with it. Acclimatization usually takes six to seven days but may be lost in as little as three days away from work. People returning to work after a holiday or long weekend -- and their supervisors -- should understand this. Workers should be allowed to gradually re-acclimatize to work conditions.

What can management do to control heat stress?

• Give workers frequent breaks in a cool area away from heat--around 25°C is ideal.
• Increase air movement by using fans where possible. This encourages body cooling through the evaporation of sweat.
• Provide unlimited amounts of cool (not cold) drinking water conveniently located.
• Allow workers time to get acclimatized. For those with previous experience in hot jobs, the regimen should be

- 50% exposure on day one

- 60% on day two

- 80% on day three

- 100% on day four.

- For new workers in a hot environment, the regimen should be 20% on day one, with a 20% increase in exposure each additional day.

• Make allowances for workers who must wear personal protective clothing and equipment that retains heat and restricts the evaporation of sweat.
• Schedule hot jobs for the cooler part of the day; schedule routine maintenance and repair work in hot areas for the cooler seasons of the year.
• Consider the use of cooling vests containing ice packs or ice water to help rid bodies of excess heat.

What can workers do to control heat stress?

• Wear light, loose clothing that permits the evaporation of sweat.
• Drink small amounts of water--8 ounces (250 ml)--every half hour or so. Don't wait until you're thirsty.
• Avoid beverages such as tea, coffee, or beer that make you urinate more frequently.
• Where personal protective equipment must be worn

- use the lightest weight clothing and equipment available

- wear light-colored garments that absorb less heat from the sun

- use clothing and equipment that allows sweat to evaporate.

• Avoid eating hot, heavy meals. They tend to increase internal body temperature by redirecting blood flow away from the skin to the digestive system.
• Don't take salt tablets unless a physician prescribes them. Natural body salts lost through sweating are easily replaced by a normal diet.

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