B-1.1, r. 2 - Construction Code

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8.133. The ambient air must be tested with a flammable vapour indicator before cutting or welding work on a petroleum equipment installation to ensure that no explosive concentration is present.
Two portable extinguishers having a minimum rating of 20-B: C must also be available on the work site while the work is being carried out.
O.C. 220-2007, s. 1.