CAW National Council 4000
Occupational Health and Safety

Heat Stress

What is Heat Stress?

Many CAW members spend some part of their working lives or days in a hot environment. Workers in CAW workplaces such as
foundries, casting, steel mills, assembly, components, laundries, kitchen and construction projects and bakeries – just to name a
few industries – often face hot conditions. Especially in the summer months, these conditions pose special hazards to their safety
and health.

Working where it is hot puts stress on our body’s cooling system. High temperatures and humidity stress the body’s ability to cool
itself and heat illness becomes a special concern during hot weather. There are three major forms of heat illness: heat cramps, heat
exhaustion and heat stroke, with heat stroke being a life threatening condition.

There are four environmental factors that affect the amount of stress a worker faces in a hot work environment: temperature,
humidity, radiant heat (such as from the sun or a furnace) and air velocity. Important to the level of stress the individual faces are
personal characteristics such as age, weight, fitness, medical condition and acclimatization to the heat.

How our bodies cope with heat

The body reacts to high external temperatures by circulating blood to the skin which increases skin temperature and allows the
body to give off its excess heat through the skin. However, if the muscles are being used for physical labour, less blood is available
to flow to the skin and release the heat.

Sweating is another means the body uses to maintain a stable internal body temperature in the face of heat. However, sweating is
effective only if the humidity level is low enough to permit evaporation and if the fluids and salt lost are adequately replaced.
Workers over 40 should be more careful because of a reduced ability to sweat. But if the body cannot dispose of excess heat, it will
store it. When this happens, the body’s core temperature rises and the heart rate increases. As the body continues to store heat,
the individual begins to lose concentration and has difficulty focussing on a task, may become irritable or sick and often loses the
desire to drink. The next stage is often fainting and ultimately death is possible if the person is not removed from the source of heat

Heat Stress hazards and their signs and symptoms

Heat Rash
, also known as prickly heat, may occur in a hot and humid environment when sweat is not easily removed from the
surface of the skin by evaporation. When extensive or complicated by infection, heat rash can be so uncomfortable that it inhibits
sleep and impedes a worker’s performance or even results in temporary or total disability. It can be prevented by resting in a cool
place and allowing skin to dry.

Heat Cramps are painful spasms of the muscles, are caused when a worker drinks large quantities of water but fail to replace their
body’s salt loss. Tired muscles – those used for performing the work – are usually the ones susceptible to cramps. Cramps may
occur during or after working hours and may be relieved by taking liquids by mouth or saline solutions intravenously for quicker
relief, if medically determined to be required.

Heat Exhaustion results from the loss of fluid through sweating when a worker has not replaced enough fluids by drinking or taken
in enough salt or both. The worker with heat exhaustion still sweats but experiences extreme weakness, fatigue, giddiness, nausea
or headache. The skin is clammy and moist, the complexion may be pale or flushed and the body temperature is normal or slightly
higher. Treatment is usually simple. The victim should rest in a cool place and drink an electrolyte solution (a beverage used by
athletes to quickly restore potassium, calcium and magnesium salts). Severe cases involving victims who vomit or lose
consciousness may require longer treatment under medical supervision.

Heat Fatigue resulting from prolonged heat exposure, causes a decline in coordination, alertness, and performance. With so much
blood going to the periphery of the body, less is available for muscles. Strength drops and fatigue kicks in sooner that otherwise.
Accidents are more likely to happen. For example, accident rates for heavy machine operators double when they work in hot

Fainting or heat syncope may be a problem for the worker unacclimatized to a hot environment by standing still in heat. Victims
usually recover quickly after a brief period of lying down. Moving around, rather than standing still, will usually reduce the possibility
of fainting.

Heat Stroke, the most serious health problem for workers in hot environment, is caused by the failure of the body’s internal
mechanism to regulate its core temperature. Sweating stops and the body can no longer rid itself of excess heat. Signs and
symptoms include:

  • mental confusion, delirium, loss of consciousness, convulsions or coma.
  • a body temperature of 41 degrees Celsius (106° F) or higher.
  • hot dry skin which may be red, mottled or bluish. Victims of heat stroke will die unless treated promptly. While awaiting for
    medical help, the victim must be removed to a cool area and his or her clothing soaked with cool water. He or she should be
    fanned vigorously to increase cooling. Prompt first aid can prevent permanent injury to the brain and other vital organs.

Susceptibility to other toxins
Heat stress can aggravate the effect of other toxins. Dehydration and
loss of minerals through sweat decreases the body’s ability to detoxify
chemicals. Because the circulatory system is under strain other hazards
increase. Carbon monoxide, which reduces oxygen supply to the
tissues, is of particular concern. Because of this, standards for other
substances should be adjusted downward for the workers in hot

Inspection of the workplace
An inspection of the workplace can help determine in advance if heat is
likely to be a hazard. The union and the Joint Health and Safety
Committee should recommend employers reduce heat stress in the
following ways:

Engineering Controls

  • Control the heat at the source through the use of insulating and
    reflective barriers (insulate furnace walls).
  • Exhaust hot air and steam produced by specific operations.
  • Reduce the temperature and humidity through air cooling.
  • Provide air-conditioned rest areas.
  • Increase air movement if temperatures is less than 35° C (fans).
  • Reduce physical demands of work task through mechanical
    assistance (hoists, lift-tables, etc.).

Administrative Controls

  • Assess the demands of all jobs and ensure monitoring and
    control strategies are in place for hot days.
  • Increase the frequency and length of rest breaks.
  • Use the ACGIH TLVs for work-rest regimes, classifying all jobs as “heavy”.
  • Schedule hot jobs to cooler times of the day.
  • Provide cool drinking water near workers and remind them to drink a cup every 20 minutes or so.
  • Assign additional workers or slow down work pace.
  • Train workers to recognize the signs and symptoms of heat stress and start a “Buddy System” since people are not likely to
    notice their own symptoms.
  • Pregnant workers and workers with a medical condition should discuss working in the heat with their doctor.

Personal Protective Equipment

  • Light summer clothing should be worn to allow free air movement and sweat evaporation.
  • In a high radiant heat situation reflective clothing may help.
  • For very hot environments, air, water or ice-cooled insulated clothing should be considered.
  • Vapour barrier clothing, such as acid suits, greatly increases the amount of heat stress on the body, and extra caution is

Union strategies for beating the heat

  • More work slowdowns, walkouts, and similar job actions occur over heat problems than any other workplace hazard. Many of
    these are effective in producing workplace change.
  • As a union we should collectively negotiate more permanent solutions to heat stress. CAW Locals should negotiate the ACGIH
    (American Conference of Government Industrial Hygienists) schedule on heat stress and ensure that all work be classified as
  • We need revised work schedules during heat waves. Increasing breaks and reducing exposure should be the number one
    administrative control of heat hazards. Heavier work can be done during cooler times. Overtime should be reduced during
    heat waves and people should work at a slower work pace during hot weather.
  • Cool down periods should be implemented in addition to workplace breaks.
  • Ensure that all workers know that they have the right to refuse work which is likely to endanger them. If it is too hot to work
    safely, don’t work.
  • “Cool Jackets” should be made available to those workers, at the expense of the employer, where engineering controls are
    not practicable (eg. foundry, casting, smelting etc.).
  • Cool rest areas are needed near the work area for breaks.
  • Isolation or insulation of hot equipment is needed as is shielding between workers and heat sources.
  • Cool drinking water should be supplied near the work area, up to 2 gallons per worker per day. Some workplaces offer
    popsicles as refreshment. While popsicles are refreshing and help to boost morale, they do almost nothing to replenish the
    water that the body has lost.

Humidex Based Heat Response Plan

Source:  CAW Health, Safety & Environment Department