Safe Escape and Rescue in Smoke
Emergency lighting and signage do not perform as expected at fire diasters. Very often systems are found to be nonoperative, not providing useful wayguidance or both. There are two common denominators: the systems are traditionally not required to be designed for smoky conditions and they are prone to failure by lack of maintenance or complexity.
A decisive factor to evacuees is the time they become exposed to heavy smoke. This time is governed by the perceived wayguidance of the evacuees - less by the length of the smoke filled escape route, which is within 16 m only in 90% of fire disasters by statistics - therefore wayfinding systems for smoky conditions play an important role.
One need to design for wayfinding in smoke exceeding OD 1.5/m in some industry as well as some public structures, contrary to current proposed general limits of OD 0.4/m within some international standardization bodies.
Careful studying has indicated a level of smoke severity and time of exposure (irritant smoke at density 1.53 to 2.26/m, exposure time 3 to 4 min, escape path 25 to 30 m) as the limit to what normal people will endure without protection - no matter what emergency egress information system is being used.
At industry plants, underground installations and complex high risk structures such as nuclear power plants or offshore drilling platforms visibility may become crucial in severe smoke. In order to perform shutdowns, extinguish fires, closing valves, rescue work or other intervening operations at imminent disaster, or indeed when all things have failed, personell may encounter very dense smoke, if ever so briefly.
Very high performance of guiding people in smoke may be provided by simple nonpowered wayfinding systems, a tactile safety hand rail system or photoluminescent marking or both. Decisive factors in designing optimum wayfinding systems for smoky conditions are continuous marking less than 1 meter above floor level, simplicity, independence of electric power, long operational times, simple maintenance and low cost.
Viewing distance, not power or luminance, is the crucial factor at high smoke density. This relies not on obscuration by distance alone, but on the simple reason that visibility of any luminance must converge to zero at 100% obscuration.
A photoluminescent strip at 0.5 m distance to the eye is more visible than the most powerful luminaries at just 1.5 m.
The photoluminescent strip built into a directional handrail in test was 25 mm wide only, and tilted to an angle of only 30゜ to the view direction. Amazingly, this design performed well even at smoke densities between OD 1.4/m and 1.5/m, but is explained by the short viewing distance.
Without respiratory protection the time available in severe smoke is approximately 50 seconds at a mean travel speed of 0.35 m/s. This is relevant to the 16 m length of escape in smoke which accounts for 90% of incidents. Thus given a good wayfinding system or a familiar route the life saving potential is very substantial. This calls for Class 1 wayfinding systems (OD＞1.5/m) and escape hoods or breathing apparatus to prevent irritation of eye and respiratory system.
Research recommend fast escape in upright or forward bent walking mode. Optimum system designs involve continuous marking at waist height at skirting board or at the floor center line.
