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Heat Wave: What Employers Need to Know About Managing Heat Stress in the Workplace

By Julie King |

Record temperatures were set last month in many cities in Ontario and Quebec, reaching highs over 33 degrees Celsius. While these numbers are well shy of the 45 degree Celsius temperature recorded in Saskatchewan in 1937, they do point to the potential for a sizzling summer ahead.

For employers, protecting your employees from heat stress at work is not just a good idea, it's required by law.

The challenge is that there are a lot of variables that affect the potential for heat exposure. An office worker will experience a temperature of 25 degrees Celsius quite differently from a construction worker who is wearing protective clothing and doing heavy labour in direct sunlight.

To help, we have researched the essentials that will help you keep your employees safe.

What are the signs of heat stress?

Our bodies are designed to maintain a constant temperature, with 38 degrees generally accepted as the upper limit of 'normal'. When taxed by extreme temperatures and humidity, our bodies will have difficulty cooling down.

Dr. Leon Jenesove, chief physician of the Ministry of Labour's Healthcare Unit in Ontario, outlines the progressive stages and symptoms of heat stress.

Early symptoms: The first symptoms include simple dehydration, fatigue and a heat rash. People can recover from these quickly, with rest in a cool area and proper hydration.

Heat exhaustion: The next stage of symptoms start with weakness and fatigue and progress to nausea, vomiting, heavy sweating and shortness of breath. It is important to seek medical attention if someone progresses to more extreme symptoms.

Heat stroke: This final stage is a life-threatening medical emergency. Someone with heat stroke cannot maintain body temperature, which will rise above 41 degrees Celsius. In this stage people stop sweating and will become confused and upset. They may go into a coma. If someone shows signs of heat stroke you must call 911 immediately.

Monitoring workplace heat risks

The science behind heat stress is pretty simple and is tied to our body temperatures. When we lose the ability to cool ourselves down, we run the risk of heat exhaustion or worse - heat stroke.

In an ideal world, employers would simply monitor the core body temperature of each worker to protect against heat stress.

Unfortunately, that is not a very practical approach. Instead, employers are asked to monitor a number of external factors to determine the risk of someone being affected by heat stress.

There are several indices that attempt to predict conditions that are dangerous for workers. In Canada, all of the provinces use guidelines set by the American Conference of Governmental Industrial Hygienists (ACGIH), notes Dr. Ollie Jay, assistant professor at the University of Ottawa, who has studied heat exposure in the Canadian workplace.

In simple terms, the ACGIH guidelines start by calculating a Wet Bulb Globe Temperature (WBGT) that looks at four main elements:

  • air temperature,
  • air flow,
  • humidity, and
  • whether or not workers are working in direct sunlight outside.

Once the WBGT has been calculated, tables of threshold levels, known as Threshold Limit Values (TLVs) are used to determine the risk to workers. This takes into account a number of other factors, including:

  • how acclimatized workers are to the heat,
  • rest periods,
  • clothing worn by workers,
  • the physical difficulty of the work, and
  • other heat sources, such as ovens, hot equipment or even the earth temperature in a mine.

Preventing heat stress

Dr. Jenesove says that as a general rule, once air temperature goes over 30 degrees Celsius you need to implement a heat plan. How you implement the plan and how quickly you act will depend on the workplace.

ACGIH also provides guidelines that will help employers develop a plan to help supervisors and workers prevent heat stress on the job:

Monitor. Follow weather alerts and if appropriate, measure the heat and humidity in the workplace to ensure they have not gone above dangerous levels. You may also need to install thermometers to monitor the WGBT in your workplace; in some provinces this is recommended, in others it is required by law.

Hydrate. Ensure that employees drink lots of fluids. The general guideline is a cup of water every 20 minutes. Employers should provide access to cool drinking water and need to remind workers to remain hydrated through the day.

Provide cool rest spaces. When employees do work in hot conditions, employers should provide access to cool rest places to help them regulate their body temperature. This could be an air conditioned area indoors or a shaded area on an outdoor job site. If possible, Dr. Jenesove recommends that you bring outdoor workers inside for breaks.

Avoid direct sunlight. Ensure that employees wear a hat if they work in the sun. Sunscreen is also recommended.

Control the pace. Slow things down. Take longer and more frequent breaks. If possible, add extra workers to help share the load. You should also schedule heavier task for cooler times of the day.

Train. It is important to train both supervisors and staff to spot the signs of heat stress. Create a buddy system and train people to monitor their buddy, because people are not good at recognizing symptoms of heat stress in themselves.

Know when to call 911. Employees and supervisors need to know what to do if someone becomes seriously ill. Dr. Jenesove stresses the importance of knowing when you need to call 911, as heat stroke can be fatal.

Be prepared. Plan ahead and make sure you have outlined processes for supervisors and workers to follow when someone starts to show signs of heat stress. In addition to setting a process to follow, make sure you have tools on hand, such as a thermometer to measure body temperature, that will be needed to evaluate and help a sick worker.

Understanding humidity: a key contributors to heat stress

On July 23, 2007 Canada's record for the highest humidex, registering at 53, was set in Carman, Manitoba. Had it risen to 54 it would have reached the point where heat stroke, and possible death, were imminent.

While temperature measures the heat of the actual air, the humidex is a Canadian invention that measures how hot the air feels to the average person, based on both the air temperature and the humidity in the air.

Environment Canada reports that discomfort will be felt in ranges from 30 to 39, with great discomfort experienced when the humidex is 40 or higher. Levels over 45 are dangerous and as mentioned above, at levels over 54 heat stroke becomes imminent.

High humidity interferes with the body's ability to get rid of metabolic heat and cool itself down, explains Dr. Jenesove, as perspiration, a key mechanism to remove metabolic heat, becomes less effective.

Dr. Jenesove notes that the humidex can be a good trigger for the following recommendations.

Humidex reaches 34: provide extra water, decrease the workload.

Humidex reaches 38: add an extra 15 minute break.

Humidex reaches 42: work shifts need to be 30 minutes on, 30 minutes off.

Humidex reaches 46: many types of labour will need to be restricted.

Provincial outlook: what Employers Must Know

Labour standards, which include things like how employers must protect workers from things like heat stress, are set by each province and territory. As usual, legislation varies from province to province.

For example, in Ontario employers are required to have an adequate heat plan.

While employers are free to develop a plan appropriate for their workplace, Dr. Jenesove notes that when the Ministry of Labour issues a heat warning, it becomes very active in enforcement with inspectors looking closely at what workplaces have in place to protect workers. Businesses can expect spot checks and if they are not meeting the standards, the Ministry could issue a compliance order.

In contrast, in Quebec the WGBT calculation is written in the legislation under Annex 5 of Regulation S-2.1,r.19.01.

(Under Quebec law, the La Commission de la santé et de la sécurité du travail (CSST) may only speak or write French when corresponding with employers based in the province. The province also published a helpful guide for employers, Confort thermique à l'intérieur d'un établissement.)

While it is a good idea to follow the guidelines set by the ACGIH, you should also check your provincial legislation.

What employees should do in a dangerous workplace

If you feel your workplace is not safe, you can complain to the Ministry of Labour in your province.

In larger workplaces you can start by raising your concern with a supervisor. If that is not effective you can speak to the safety committee - if that fails to get results you can call the labour standards body in your province or territory to complain.

You can expect the government to send an inspector to investigate the complaint and issue a compliance order to the employer if it is found to be valid.

Further reading & resources

ACGIH website

Heat Stress Guideline, Ministry of Labour, Ontario

Confort thermique à l'intérieur d'un établissement

Humidex-Based Heat Stress Calculator

Extreme Hot or Cold Temperature Conditions

Hot Environments - Control Measures

Environment Canada's Humidity Fact Sheet

Weather extremes in Canada

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