To limit the probability that the performance of polyethylene sheets will fall significantly below expectations, which could lead to an inability to resist loads induced by air pressure differences, which could lead to the sheets rupturing or tearing at fasteners, or becoming prematurely brittle, which could lead to the failure of the membrane.
Where the air barrier system separates a garage, or suite containing a garage, from residential space, this is to limit the probability of a loss of airtightness, which could lead to gas and fumes migrating from the garage into the remainder of the building, which could lead to the accumulation of gas and fumes and their subsequent ignition by a nearby ignition source, which could lead to a fire or explosion, which could lead to harm to persons.