Exit Signs in Smoke: Design Parameters for Greater Visibility

A review of regulations and specifications for internally illuminated exit signs recommended or enforced by various sanctioning bodies in Canada, Great Britain and elsewhere reveals omissions and inconsistencies which may compromise the safety of building occupants in smoke. Since these problems are partly due to lack of conclusive research, a controlled psychophysical experiment was conducted to assess the readability of three common exit sign design features (i.e. the various combinations or opaque and transilluminated text and backgrounds) under different levels of smoke density and ambient illumination. The sign designs differed greatly in terms of threshold illuminance at the rear of the signs (analogous to the intensity of the sign's light source), but all were similar in terms of the threshold luminance of the sign’s front panel. Based on these findings, recommendations are made for improved building codes.