In the absence of other lights in the test chamber, signs of conventional design were visible through 2-5 m of smoke of a lower density than that found in many fires. When additional illumination sources were introduced, visibility was substantially reduced. Just as fog particles scatter light from car headlamps on full beam, smoke particles scatter ambient light and absorb light from the target, reducing visibility at high ambient light levels. It should also be recognized that loss of vision is by no means the only danger from smoke. The hazard is not completely described by the degree to which vision is obscured.
Smokes are toxic, albeit to differing degrees.
Exit Signs Exit signs are important indicators of evacuation routes in emergencies such as fires, particularly if the exit route is unfamiliar. The signs must be plainly visible, in direct line of sight, and well separated from other signs. It has been demonstrated that it takes relatively little smoke to obscure exit signs or make them difficult to see. 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.