Abstract
Visibility is a crucial factor affecting human behaviour and safety during fire emergency evacuations. Adequate evaluation of visibility through smoke will assist in the design of fire safety systems, particularly the smoke control and signage systems, in built environment to maintain tenable conditions and guide occupants to safety during fire emergencies. In the chapter, an appraisal of previous studies on visibility through smoke is presented. Some fundamental concepts and physics of light transmission are discussed. Based on the review, a theoretical framework is established for attenuation of light from two kinds of sources that resemble the warning and exits signs commonly and mandatorily installed in built environments. This framework incorporates both the divergence effect of light rays from light-emitting sources and attenuation effect by smoke. Light sources for emergency warning and signage are categorised into point sources and panel sources. For a point source the simple differential equation for divergence effect is merged with that accounting for the attenuation effect by smoke. The straightforward solution for light intensity is presented as a function of distance from the source as well as smoke extinction coefficient. For a light emitting panel, the concept of view factor in the radiation heat transfer theory is applied to account for variation in light intensity (luminance) as a function of position (distance and angle) relative to the panel. The resultant function is moderated by the smoke attenuation factor to give the total variation in luminance. A method is then developed for the evaluation of visibility of warning lights and exit signs in heterogeneous smoky conditions. This method is based on an empirical correlation obtained by previous researchers in the literature and with further consideration of attenuation of luminance along the line of sight from the observer to the light source. The application of this method can be extended to the processing of computational fluid dynamics simulation results to obtain visibility of exit signs through smoke. The advantage and limitations of the new method are discussed. Recommendations for future research are presented at the end.
Original language | English |
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Title of host publication | Critical Issues and Analysis in Fire Protection and Prevention |
Editors | Axel Cable, Brady Manescau |
Place of Publication | U.S. |
Publisher | Nova Science Publishers |
Pages | 39-69 |
Number of pages | 30 |
ISBN (Electronic) | 9781536187960 |
ISBN (Print) | 9781536187380 |
Publication status | Published - 2020 |
Keywords
- visibility
- fire prevention
- smoke
- safety