To limit the probability that:
- hydraulic load from fixtures discharging simultaneously
will lead to siphonic action or back pressures,
- discharge from water closets will lead to the siphonage
of downstream traps,
- hydraulic load from fixtures located on higher storeys
will lead to trap seal failure due to compression of air below the
- the failure of wet vent sections to conform to wet vent
requirements will lead to siphonic action or back pressures.
This is to limit the probability of
trap seal failure in a vent stack that functions as a wet vent, which
could lead to the entry of sewer gases into occupied space, which
could lead to negative effects on indoor air quality, which could
lead to harm to persons.