Intent 1:
To limit the probability that the outdoor air supply
flow will not be equal to the normal operating exhaust capacity of
the principal ventilation fan, which could lead to:
- excessive negative pressure, or
- excessive positive pressure.
This is to limit the probability of:
- where there is excessive negative pressure:
- the ingress of soil gases (such as methane and radon),
- the spillage of combustion products from fuel-burning
appliances that are susceptible to spillage, or
- moisture ingress from the ground, or
- where there is excessive positive pressure, condensation
within assemblies.
This is to limit the probability of negative effects on
the air quality of indoor spaces, which could lead to harm to persons.