If it is assumed that signs may not always be adequate to guide occupants to a place of refuge, the designer must ensure that building occupants are not exposed to smoke. While this is excellent advice, people do sometimes find themselves exposed to smoke. In such cases the present requirements may not provide adequate indication of escape routes. People taking part in the study consistently found it easier to see bright signs through smoke. The number and location of signs should minimize the distance between observer and sign at all times.
Transmission of light falls off with distance, so that apparent brightness also is diminished.
Placement Low placement of signs on walls may increase visibility in the early stages of a fire. In some countries exit signs are always placed low on walls rather than above doors, as is customary in Canada, because smoke tends to travel along the ceiling when it mixes with hot, buoyant fire gases. As these gases cool, however, the smoke sinks and eventually fills the entire space. Smoke may also be dispersed evenly through rooms by forced ventilation systems and by the action of sprinklers activated by the fire. Under these conditions low placement of exit signs may offer little advantage.