Nine factories tested emergency sirens on Tuesday afternoon in Montreal.
The sirens alert the public to get indoors immediately to avoid a toxic and potentially lethal release of dangerous gases.
In the event of a real emergency, anyone who hears a siren should immediately enter the nearest building, close all doors and windows, and take shelter until authorities give the all-clear.
In Tuesday's test, sirens blasted for three minutes between 2 and 3 p.m.
The city of Montreal also issued alerts about the tests, and several TV and radio stations broadcast messages about the tests.
The factories taking part Tuesday were:
- Metro Richelieu - Atlantic fish distribution centre: 3785 Francois Bricault St. 500 metre radius
- Metro Richelieu - Meat and frozen food distribution centre: 11,701 Albert Hudon Blvd., 335 metre radius
- Indorama PTA Montreal (IVPTA): 10,200 Sherbrooke St. E. 1,523 metre radius
- Suncor Sulphur factory: 11,450 Cherrier St. 1,300 metre radius
- Molson Coors: 1550 Notre Dame St. E. 445 metre radius
- Labatt Brewery: 50 Labatt St. 1,800 metre radius
- Saputo inc.(St. Laurent complex): 2365 Cote-de-Liesse. 1,100 metre radius
- Saputo Milk Products (St. Leonard complex): 7,750 Pascal Gagnon St. 770 metre radius
- Parmalat Canada Inc.: 7,470 Saint Jacques St. West. 1,860 metre