To limit the probability that the performance of the coating, with respect to resistance to vapour diffusion, will fall significantly below expectations, which could lead to insufficient control of vapour diffusion through environmental separators under expected environmental loads, which could lead to condensation.
This is to limit the probability of deterioration, which could lead to compromised structural integrity of the separators or of elements supported or protected by the separators, which could lead to structural failure, which could lead to harm to persons.