To limit the probability that vapour-either in the room or space or while being exhausted from the room or space-will come in contact with ignition sources within or conveyed by ventilation systems serving other areas, which could lead to the ignition of the vapour, which could lead to harm to persons.
To limit the probability that vapour will migrate through the ventilation system to other areas of the building, which could lead to the accumulation and subsequent ignition of the vapour from a nearby ignition source, which could lead to harm to persons.
To limit the probability that fire originating in the room or space will spread to other parts of the building, which could lead to harm to persons.