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Heat Warning

Image of young child standing in the shadeWhile it is important to enjoy the outdoors during the summer, it is also important to remember that extreme heat and humidity can cause serious health problems.

What is a heat warning/extended heat warning and when is it issued?

  • Heat Warning: When forecast temperatures are expected to be at least 31°C and overnight temperatures are above 20°C for 2 days or the humidex is at least 40 for 2 days.
  • Extended Heat Warning: When forecast temperatures are expected to be at least 31°C and overnight temperatures are above 20°C for at least 3 days or humidex is at least 40 for at least 3 days.
  • Residents that would like to receive email notification of heat events can sign up for e-alerts.
  • Smog can often accompany extreme heat.

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What is Humidex?

Humidex describes how hot, humid weather feels to the average person. Humidex values are calculated using temperature and humidity.

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Who is at greatest risk from extreme heat?

While extreme heat and humidity can put everyone at risk for heat illnesses, those at greatest risk include:

  • older adults (over the age of 65)
  • infants and young children
  • people with chronic illness e.g. heart disease, asthma
  • people with physical or mental disabilities
  • people who work in the heat
  • people who exercise in the heat
  • people who have limited resources to protect themselves

Obesity, dehydration, fever or infection, sunburn and alcohol use also increases a person’s risk from extreme heat.

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What are heat illnesses?

  • Heat illness occurs when a person’s body temperature rises quickly and sweating is not enough to cool the body properly.
  • High body temperature can lead to heat stroke, heat exhaustion, heat fainting, heat cramps (muscle cramps), heat rash and heat edema (swelling of hands, feet and ankles).
  • Heat illnesses are preventable.

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Heat stroke is a medical emergency.

Call 911 immediately if you notice that someone has a high body temperature and is either unconscious, confused or has stopped sweating.

While waiting for help, cool the person right away by:

  • moving them to a cool place, if you can
  • applying cold water to large areas of the skin or clothing
  • fanning the person as much as possible

What are symptoms of heat illness?

  • dizziness or fainting
  • nausea or vomiting
  • headache
  • rapid breathing and heartbeat
  • extreme thirst
  • decreased urination with unusually dark yellow urine

If you experience any of these symptoms during extreme heat, immediately move to a cool place and drink liquids. Water is best.

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How can I prevent heat illness?

You can avoid heat illness by doing the following:

  • Pay close attention to how you – and those around you – feel.
  • Frequently visit neighbours, friends and older family members, especially those who are chronically ill, to make sure that they are cool and hydrated.
  • Reschedule or plan outdoor activities during cooler parts of the day.
  • Block sun out by closing awnings, curtains or blinds during the day.
  • Avoid sun exposure. Wear a wide-brimmed hat or use an umbrella.
  • Wear loose-fitting, light-coloured clothing made of breathable fabric.
  • Drink plenty of cool liquids, especially water, before you feel thirsty to decrease your risk of dehydration.
  • Prepare meals that don’t need to be cooked in your oven.
  • Take a break from the heat by spending a few hours in a cool place e.g. tree-shaded area, swimming facility or air-conditioned site.
  • Use a fan to help you stay cool.
  • Take cool showers or baths until you feel refreshed.
  • Never leave people or pets in your care inside a parked vehicle or in direct sunlight.
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Are there cooling centres in Halton?

Yes. In the event of an extreme heat warning, there are a number of cooling centres and places that you can visit including swimming pools, splash pads and air-conditioned public facilities.

Visit your local municipal website for locations and hours of operation:

Other air conditioned public places are available, including malls and movie theatres.


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What can I do to help prepare for extreme heat events?

  • Ensure that air conditioners are working properly.
  • If you are taking medication, ask your doctor or pharmacist if it increases your health risk in the heat.
  • Choose light-coloured paint for the exterior of your home and other surfaces e.g. deck, patio.
  • Consider planting a broadleaf tree on the side of the house where the sun hits during the hottest part of the day to provide shade and shelter to the house.

The information provided on this website is based on content from Health Canada’s Climate Change and Health Resources (external link).

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Halton-Peel Heat Warning Totals to Date

  Total # of Heat Warning Total # of Days
2018 5 16
2017 3 7
2016 7 21
2015 4 12
3 10
6 8
5 13
2010 4 12
2009 3 3
2008 1 4
2007 5 10
2006 4 11
2005 8 30
2004 1 1
2003 3 4

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