To limit the probability that an outdoor air supply fan will not be installed or that an inadequately sized outdoor air supply fan will be installed, which could lead to the excessive depressurization of dwelling units, which could lead to the spillage of combustion products from fuel-burning appliances that are susceptible to spillage.
This is to limit the probability of the entry of carbon monoxide gas into living space, which could lead to the acute poisoning or asphyxiation of persons.