Reappraisal of Jin's visibility through fire smoke experiment: Insights into signage visibility and the impact of ambient light

Jin's experiments in the 1970s contributed to fire evacuation research, but only examined relatively high ambient light levels. By replicating the Jin's experimental setup and varying ambient light level, we explore the relationship between smoke extinction coefficient, background illumination and signage emitting light intensity under low-light real-world emergency scenarios. Firstly, we confirm Jin's observation of a linear relationship between smoke extinction coefficient (sigma) and visibility distance (V), although our measurements of sigma are 7–11% higher under equivalent signage luminance. Our findings on the sigma versus normalized brightness at a 15.5 m distance align with Jin's results, while a 20% discrepancy is observed at 10.5 m and 5.5 m distances. At high ambient light (180 lx), the K=sigma*V is comparable in Jin's experiment (from 5 to 8) and this work (from 4.7 to 9.5). However, at low ambient light (less than 22 lx), the signage remains visible in higher smoke extinction coefficients (with K from 6 to 11). The critical extinction coefficient decreases by nearly 40% for every 5 m increase in visibility distance. This work deepens the understanding of smoke visibility under a dark fire environment, which may help guide fire signage design and inspire new fire evacuation research.