To limit the probability that the location of the dispensers in a basement or on upper storeys will lead to delays or ineffectiveness in conducting firefighting operations in the event of a fire emergency, which could lead to the spread of the fire beyond the point of origin, which could lead to harm to persons.
To limit the probability that location of dispensers in a basement will lead to accumulation of vapours in low areas of a building, which could lead to ignition of vapour from a nearby ignition source, which could lead to harm to persons.