Santé Montréal

Heat and extreme heat

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Oppressive heat

Environment Canada issues "heat alerts” when the temperature reaches 30 °C and the humidex (temperature and humidity combined) reaches 40 °C.  The main effect of heat on the population is discomfort.

Extreme heat

The term “extreme heat” was defined by public health authorities in reference to anticipated heat events likely to have an impact on the health of vulnerable individuals. In Montréal, an "extreme heat" episode is defined as 

  •  three consecutive days when the average maximum temperature reaches 33 °C and the average minimum temperature doesn’t drop below 20 °C,  
  • or when the temperature doesn’t drop below 25 °C for two consecutive nights.  

Environment Canada doesn’t issue extreme heat alerts, but its weather forecasts are used to predict situations which could cause health problems.  

Did you know...

Some people are at greater risk of developing health problems during extreme heat episodes, especially older people, people with chronic conditions, people with mental health problems (including drug or alcohol addiction) and children 4 years old or younger.

  • There have been at least four extreme heat episodes in the Montréal region since the 1980s. The most recent occurred in 2018 and resulted in about 60 deaths.
  • The main health problems linked to heat are dehydration (dry mouth), headaches, dizziness, confusion and fainting.
  • In the presence of these symptoms, it is recommended to call Info-Santé at 8-1-1 or talk to a health professional. 
  • If there is fever in addition to those symptoms, this may be heatstroke, which is a medical emergency.  In this case, call 9-1-1 to get help.
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When to Consult

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Protection and prevention

When it’s very hot, it’s important to

  • spend a few hours a day in a cool, preferably air-conditioned place;
  • drink a lot of water, even before you feel thirsty;
  • reduce physical effort.

During heat waves, check in regularly on older people and people with chronic diseases or mental health problems (including alcohol or drug addiction) to make sure they’re taking the recommended preventive measures, and to help them should they need it.  

Older people and people with physical or mental health problems

To find out about what to do during heat waves, people at risk as well as friends and family members can consult the fact sheet It’s really hot! (PDF).

Information on heat episodes is also available in other languages. Click on the language of your choice to download the documents:

Preventive measures in various languages:

People with mental health problems

People with mental health problems can also find out more by downloading the fact sheet on heat and mental health (PDF).

Children 0 to 4 years old

Children aged 0 to 4 years are also very vulnerable during heat waves. To find out about precautions to take, consult the fact sheet It's really hot! (PDF)

Documentation for parents and other caregivers of children aged 0 to 4 years available in different languages (PDF): 

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Risk factors

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Help and Resources

Where to get additional credible information

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People at Risk

Everyone should take precautions during heat waves and periods of extreme heat. However, some people are at greater risk:

  • Older adults
  • People with chronic diseases like diabetes, and cardiovascular, respiratory, kidney and neurological diseases
  • People with mental health problems, especially schizophrenia and alcohol or drug addiction
  • Children aged 0 to 4 years
  • Workers:

    • Employers in Montréal and their employees, especially in construction and city workers
    • Regardless of the type of job, working when it’s hot presents health risks, especially during the first few days of a heat wave. The body needs time to get used to rising temperatures. This is especially true for workers performing continuous challenging physical tasks in poorly ventilated places or under the sun.
    • Various preventive measures must be taken: in addition to drinking a lot of water and covering yourself with light clothing to protect from possible heatstroke, see the CNESST’s advice on preventing heatstrokes. This advice also helps you recognize the first signs of heatstroke and what to do if a colleague or employee starts showing signs.

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Dernière mise à jour le : 2019.05.15