If you hear the warning siren, immediately go inside the nearest building. When there is an industrial accident, chemicals can be released in the air and form a toxic cloud.

• Close doors and windows, and use rags to block any ventilation openings. Turn ventilation systems off to keep toxic substances out. Stay away from doors and windows. 
• Listen to the radio to know what is happening and get instructions from the authorities. 
• Leave your children in school to avoid exposing them or yourself to the toxic substance. 
• To keep lines free for emergency help, avoid using your phone unless you are calling 911 to report an emergency.

When an alarm goes off, the siren produces a rising and descending tone that lasts for three minutes. Depending on the factory, the sound is heard within a range of 335 to 1860 metres. The siren’s range may be affected by the weather. The warning siren does not sound the same as the interior sirens of some factories in eastern Montréal. These can be heard every Tuesday around 11 a.m.

Listen to the sound of a warning siren in this video.