Hot summer temperatures can create uncomfortable, and sometimes dangerous, conditions.  But outdoor environments aren’t the only workplaces that can be extremely hot.  Many indoor occupations also involve exposure to excessive heat.  Too much heat, or heat stress, can cause discomfort or illness and can sometimes be fatal.

Understanding Heat Stress
Your body relies on sweating and the subsequent evaporation of sweat to keep you cool.  It also gives off excess heat through the skin in order to maintain a safe core temperature.   In hot environments where the body cannot cool quickly enough, a number of heat-related illnesses could result.  Common heat disorders, in order of increasing severity, include:

• Heat rash (prickly heat)
• Heat edema (swelling)
• Heat cramps
• Heat syncope (fainting)
• Heat exhaustion
• Heat stroke.

Heat stroke can be fatal if not treated immediately.¹  Furthermore, victims won’t usually be able to recognize their own heat stroke symptoms – so it’s important that others recognize what’s happening.  Common symptoms include: weakness; confusion or strange behaviour; difficulty breathing; hot, dry, red skin; elevated pulse; headache or dizziness.  At advanced stages of heat stroke the victim may pass out or have convulsions.^2,3  Call for medical help immediately, remove excess clothing from the victim, offer sips of cool water, and fan or spray the victim with cool water.²

The degree of heat stress experienced by a worker depends on environmental factors and the individual’s characteristics.  Air temperature, humidity levels, the amount of radiant heat, and air velocity all contribute to heat stress levels.  So do personal traits such as age, weight, degree of fitness, medical status, and acclimatization to heat.⁴

Managing Heat Stress in the Workplace
There are several strategies that can be used to minimize the effects of workplace heat stress.

Use Engineering Controls

• Use fans to move air and enhance evaporation (effective if the air temperature is less than 35C, 95F).
• Local exhaust ventilation can be used to remove hot air or steam before it mixes with general room air.
• Minimize the impact of radiant heat by insulating hot surfaces or with shielding placed between the radiant heat source and workers.
• Reduce humidity with air conditioners or dehumidifiers.

Acclimatize Workers

• Gradual exposure to heat will help workers cope with high temperatures.  Complete acclimatization normally takes about one to two weeks for healthy workers.

Keep Them Hydrated

• Water lost through sweating must be replaced.  Workers should drink 250 millilitres (1 cup) of water every 15 to 20 minutes.
• Don’t rely on thirst to determine when water is needed.
• Avoid drinking caffeine, alcohol, and sweet beverages.
• Salt replenishment is not recommended. 

 Regulate the Pace of Work

• Provide frequent rests away from heat sources to allow the body to compensate for heat exposure.  The American Conference of Governmental Industrial Hygienists (ACGIH) has published work-rest regimens for various working scenarios (see Reference 5).

 Manage Exposure Time

• Schedule outdoor work during cooler times of day if possible.
• Rotate workers in hot jobs to minimize each individual’s overall exposure time.

Dress Properly

• This often requires a balance between dressing for safety and dressing to keep cool.
• If possible, wear clothing that allows sweat to evaporate.
• Use insulated clothing or reflective clothing for work in high radiant heat.
• Cooling can also be provided with ice vests and air-conditioned respirators.

Provide Training

• Workers and supervisors should know about the adverse effects of working in hot environments, how to recognize the symptoms of heat disorders, first aid procedures, as well as the benefits and procedures for managing heat stress in their workplace.

Useful References

1. “Too Much of a Good Thing – The Hazards of Summer Heat”, Health & Safety Report, Volume 2, Issue 6, June 2004, Canadian Centre for Occupational Health & Safety.
2. Working in Hot Environments: Health & Safety Guide, Canadian Centre for Occupational Health & Safety, 96 pages, 2005.
3. “OSHA Quick Card – Protect Yourself: Heat Stress”, US Department of Labor, Occupational Safety & Health Administration, www.osha.gov/Publications/osha3154.html
4. “Protecting Workers in Hot Environments”, Fact Sheet No. OSHA 95-16, U.S. Department of Labor, Occupational Health & Safety Administration, 1995.
5. 2006 TLVs and BEIs, American Conference of Governmental Industrial Hygienists, Cincinnati, www.acgih.org/store
6. “Working in Hot Environments”, U.S. Department of Health & Human Services, National Institute for Occupational Health & Safety (NIOSH), April 1986.