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: