Visibility through Fire Smoke (III)

Abstract

In the preceding experiments, the signs have been obsereved through a glass window and the influence of stimulating effect (Lachrymal and Irritant effect) of smoke on visibility has been omitted.
In the present paper, to investigate such influence, observers walk to the back-lighted “EXIT” sign in the smoky corridor (20 meters long) and record the visibility at the obscuration threshold, at the distinguishable threshold of color, and at the legible threshold of letters of the sign (see Fig. 2). Fluoresent lamp of 10 W for normal operation and 3 pieces of tungsten filament lamps (2.5 V, 0.3 A) for black out are employed as the light source of sign (see Fig. 1). The stimulating smoke was generated from smoldering wood (neary white smoke), and unstimulating smoke was generated from kerosene (black smoke).
The visibility at the distinguishable threshold of color and at the legible threshold of letters of the sign in high stimulating smoke density (0.5/m of extinction coefficient) reduces by more than 30% compared with those in the same unstimulating smoke density (see Fig. 4 and Fig. 5). In stimulating smoke, especially high in density, it is more difficult to observe a sign because of lachrymation and irritation. Therefore, the apparent brightness contrasts of the distinguishable threshold of color and of the legible threshold of letters of the sign require large value compared with that in the same unstimulating smoke density (see Fig. 6 and Fig. 7). That is the reason why visibility in stimulating smoke is small.
Both the visibilities at the obscuration threshold of sign in stimulating and unstimulating smokes are about the same, because the apparent brightness contrast of obscuration threshold is little affected by stimulating smoke (see Fig. 3, Fig. 6 and Fig. 7).