B-1.1, r. 2 - Construction Code

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8.45. If construction work consists in removing petroleum equipment from the ground, the contractor or owner-builder must, as the case may be,
(1)  empty all petroleum product from the tank, piping and motor fuel dispensers, before their removal;
(2)  remove the tank and piping from the ground and from the site along with the motor fuel dispenser connected to it, after purging the tank of all vapours until the flammable vapour concentration is less than 20% of the lower explosive limit; or
(3)  destroy the tank as provided by section 8.68 or have it approved as provided by section 8.44, in which case it must be purged of any vapour and its openings must be hermetically sealed other than a ventilation opening of at least 60 mm in diameter.