The high intensity PL materials offer luminance with a safety margin. These wayfinding marking systems are even less susceptible to design flaws, abuse or degradation over time than their predecessors. They require a longer activation time, but accept a low charging illuminance and the brighter and long-lasting luminance makes up for this deficiency.
Applications
A stronghold of PL marking is the underground power plant industry. Most of Norway's 863 hydro power plants are equipped with PL linear marking for wayfinding and rescue operation in power outings or smoke. In Sweden an underground power plant caught fire and two survivors insisted they would have perished without sticking to the PL lines.
The new Oslo Gardermoen Airport is equipped with the novel PL in underground areas, train terminal and tunnels. Both linear marking and signs are made to perform better than 300/45 mcd/m2, surpassing conventional zinc-sulphide PL by a factor of 20. Tunnels challenge PL systems as charging lights from passing trains and vehicles may be scarce.
Following the attack at the World Trade Center in New York the high rise towers are provided with PL linear marking. All lighting power supplies in stairwells broke down in 12 minutes. The evacuation in dense smoke took seven hours.
The many hazards at North Sea Oil Rigs require escape marking to be both effective and reliable. Disasters such as the Piper Alpha oil rig, the Herald of Free Enterprise ferry and the Scandinavian Star ferry pointed at the hazards of inadequate marking and power supplies. The new marking materials points to a definite solution. The PL manufacturing industry express great expectations of increase in both offshore and maritime applications.
When accidents involve fire, explosion, collapse, shortcircuiting or ingress of water all electrical systems including emergency power supplies are at risk. Therefor, PL are increasingly used in road and train tunnels.
It is no wonder then, that PL systems have been tested and deemed adequate by FAA and the larger airlines to replace electroluminescent marking of the aisles in aircraft. The heavy metal pigments fulfilled the requirements of 11 hours for longhaul airplanes and provided intense visible delineation to the end of test at 16 hours.
When All Fails
There is no neon glamour or fancy features in PL wayfinding. There is no flood light luminance, no self-checking, no high-tech bulb fault reporting features and no long lasting battery packs to boast of. But if all fails, PL perform. There is virtually nothing that may go wrong: You may even remove or obscure parts of the marking or keep the escape route in total darkness for a whole working shift period without preventing PL to perform when called upon.
Electrically powered emergency lighting is a completely different concept that complement rather than substitute PL escape route marking. Emergency lighting ensure illumination when normal lighting fails and support PL in large public spaces to mark exits from a distance, or in smoky conditions to help identify these exits at close range. Electrified low location lighting (EP) is an alternative in luminance. But like emergency lighting EP is prone to an array of failure modes by itself and suffer a bad record of reliability and cost. Point sources of light are easily obscured by smoke and a survey concluded their performance as a wayfinding system is very low - only 8 % of evacuees in real fire catastrophies noted the presence of these.
Low location marking with PL provide reliable wayfinding safety in the worst of conditions. A Finnish study recommends linear PL as prime marking system in the most extreme of smoke.
Breathing Apparatus Required
Without breathing apparatus humans may not survive a minute of smoke densities exceeding roughly OD 1.5/m. At this density EP single light sources beyond 2 m is totally obscured. A PL handrail at 0.5 m viewing distance is useful at much denser smoke. But users must wear eye protection or breathing apparatus. In fact, eye irritation prevents effective use of visual aids from OD 0.2/m on. A 1993 study concludes directional tactile handrails may provide superior wayfinding performance in smoke more dense than OD 1.5/m - with or without visual PL/EP strips embedded.
The Low Location Lighting Objective
The objective of wayfinding systems for evacuation is to guide all persons to a safe haven as orderly, fast and unambiguously as possible. A flaming fire create a smoke layer against the ceiling in the fire room and vicinity leaving better visibility at floor levels. The smoke layer obscure point sources of light very quickly. The idea of low location lighting evolved on this during the 80-ies. Others realized that away from the fire vicinity smoke become evenly dispersed due to cooling and that marking systems must be linear to be visible. At first one kept mixing the ideas of low location, lineation and point sources of light. This led to delineated spaced EP point sources of high luminance at floor level. But in fact, linear marking perform best at eye level in evenly dispersed smoke and does barely require any luminance at all. Therefore fully linear PL systems emerged and performed equally well or best in tests.
