Extreme Heat

Each summer, London and Middlesex County experience periods of extreme heat. The Middlesex-London Health Unit issues the following when one or more of the criteria are met:

Heat Warning

• Environment and Climate Change Canada issues a forecast calling for a daytime high of 31^oC or higher and a forecast low of 20^oC or higher for two consecutive days, or;
• Environment and Climate Change Canada issues a forecast calling for a Humidex of 40 or higher for two consecutive days, or;
• Environment and Climate Change Canada Forecasters anticipate that actual temperatures and humidex values in London and Middlesex County will reach the thresholds noted above.

Extended Heat Warning

• Environment and Climate Change Canada issues a forecast calling for a daytime high of 31^oC or higher and a forecast low of 20^oC or higher for three consecutive days or longer, or;
• Environment and Climate Change Canada issues a forecast calling for a Humidex of 40 or higher for three consecutive days or longer, or;
• Environment and Climate Change Canada Forecasters anticipate that actual temperatures and humidex values in London and Middlesex County will reach the thresholds noted above.

Individuals at high risk of heat-related illness¹

During a heat wave, everyone is at risk, but some groups are more vulnerable than others. They include:

• infants and young children
• people who are pregnant
• older adults
• people who live alone
• people with chronic medical conditions (for example, heart disease, respiratory conditions, overweight, diabetes) or mental illnesses (for example, schizophrenia, depression, dementia)
• people on certain types of medications (for example, for high blood pressure, for mental illnesses, etc.)
• people experiencing homelessness, those who are underhoused, or encounter other challenges in accessing cool spaces
• people with limited mobility
• people who exercise vigorously outdoors (play sports, cyclists, gardeners)
• outdoor workers (depending upon length or time and exertion levels)
• people who work in places where heat is emitted through industrial processes (for example, foundries, bakeries, dry cleaners)*

*Please see the Ministry of Labour, Immigration, Training and Skills Development's Managing Heat Stress at Work website for further advice.

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Symptoms of heat-related illness¹

Adverse health effects that can occur from exposure to excessive heat include:

• heat rash: red or pink rash usually found on the neck, chest and/or elbow creases
• heat cramps: painful muscle cramps
• heat exhaustion: heavy sweating, weakness, dizziness, nausea, vomiting and fainting
• heat stroke: headache, dizziness, confusion, fainting and high body temperature; skin may be hot and dry or damp; this is a medical emergency – seek emergency help and cool the person down right away

Other health problems can also occur, especially for those with chronic medical conditions such as heart disease or diabetes.

Consult a healthcare provider or call Health811 (TTY: 1-877-797-0007) if you experience any of the above symptoms.

In the event of medical emergency (for example, loss of consciousness), call 911 or your local emergency number immediately.

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Things you can do to protect yourself²

Prepare for the heat

• Tune in to local weather forecasts and alerts so you know when to take extra care.
• Find ways to keep cool before the hot weather starts. If you have an air conditioner, make sure it works properly. Find an air-conditioned spot close by where you can cool off for a few hours on very hot days. This will help you cope with the heat.
• Have drinks in your vehicle and keep your tank filled or car charged in case you need to get somewhere cool quickly.
• Arrange for regular visits by family members, neighbours or friends during very hot days in case you need help. Visitors can help identify signs of heat illness that could be missed over the phone.

Pay close attention to how you, and those around you, feel

Watch for symptoms of heat exhaustion, which include:

• headache
• nausea or vomiting
• dizziness or fainting
• rapid breathing and heartbeat
• extreme thirst (dry mouth or sticky saliva)
• decreased urination with unusually dark yellow urine
• changes of behaviour in children (like sleepiness or temper tantrums)

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

Heat stroke is a medical emergency! Watch out for the signs and symptoms of heat stroke which may include:

• high body temperature
• confusion and lack of coordination
• dizziness or fainting
• very hot or red skin

If you or anyone in your care experiences any of these signs and symptoms, call 911 immediately. While waiting for help, cool the person right away by:

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

Stay hydrated

Drink plenty of liquids (especially water) before you feel thirsty to decrease your risk of dehydration (not having enough fluids in your body). You may be dehydrated even if you are not thirsty. Stay hydrated.

• If you eat less, you may need to drink more water.
• Drink water before, during and after physical activity.
• Remind yourself to drink water by leaving a glass by the sink.
• Eat more fruits and vegetables as they have a high water content.
• Flavouring water with natural fruit juice may make it more appealing.

Stay cool

Dress for the weather

• Wear loose-fitting, light-coloured clothing and a wide-brimmed hat made of breathable fabric.
• When you buy sunglasses, make sure they provide protection against both UVA and UVB rays.

Take a break from the heat

• If you must do physical activity in extreme heat:
• take extra breaks
• drink lots of water
• remove gear to let your body cool off
• Don't expect your usual performance in hot weather. Give your body time to recover after being in the heat.

Keep your home cool

• Make meals that don't need to be cooked in an oven.
• Block the sun by closing awnings, curtains or blinds during the day.
• If possible, open your windows at night to let cooler air into your home.
• If you have an air conditioner, be sure to turn it on before it gets hot. If you are using a window air conditioner, cool only 1 room where you can go for heat relief.

If your home is extremely hot

• Take cool showers or baths until you feel refreshed.
• Spend time in a cool place. It could be a tree-shaded area, swimming facility or an air-conditioned spot like a shopping mall, grocery store or public library.

Avoid exposure to extreme heat when outdoors

Never leave people or pets inside a parked vehicle or in direct sunlight.

Reschedule or plan outdoor activities during cooler parts of the day.

• Plan strenuous outdoor activities for cooler days.
• Choose a cooler location like a place with air conditioning or a spot with shade such as from a tree.

Avoid sun exposure. Find or bring shade when possible.

• Use an umbrella.
• Choose a spot with shade such as from a tree or awning.

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Additional Resources

• For brochures and posters on how to prepare for the heat, please view Health Canada's resources for extreme heat. There is additional information for healthcare providers and industry as well.
• For a listing of cooling centres, pools, spray pads and wading pools and their hours of operation visit the City of London websites or call 519-661-5575.
• For the addresses of local libraries, please visit the London Public Library website or call 519-661-4600.
• Call Health811 by dialing 811 (TTY: 1-877-797-0007) for free advice from a Health Professional, 24/7.
• For pet care information, please visit the London Animal Care Centre website or call 519-685-1330.

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Copyright

Please note: Where indicated, the source of the information on this web page is the © King's Printer for Ontario OR the Government of Canada's Extreme heat events: How to protect yourself from the health effects of extreme heat web page, which is a copy of the version available at the URL in the references section below.