B-1.1, r. 2 - Construction Code

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8.99. Vent piping for an underground tank must be installed so that it is free from any device likely to cause back pressure exceeding the allowable stress for the tank.
In the case of an underground tank to be used to store a Class 2 or Class 3 petroleum product, vent piping may be fitted with return bends, coarse screens or other devices designed to minimize the entry of material.
O.C. 220-2007, s. 1.