Wayfinding and Rescue in Heavy Smoke or Blackouts:
Low Tech Marking Outperform Sophisticated Concepts
Geir Jensen
InterConsult Group ASA
Newly recognized earth-borne pigments have made a ten-fold improvement in luminance of photoluminescent (PL) wayfinding systems and removed doubts of deficiency. The debate on 'sufficiently visible or not' has shifted to a discussion on how much the width of marking lines may be reduced and still conform.
Due to a comfortable margin for error new products tolerate minor design flaws, periodic loss of charging light, blackouts in excess of 10 hours or degradation caused by aging or dirt.
The superior reliability, low cost and unmistakable marking of earlier zinc sulphide PL systems has been retained.
The PL manufacturing industry concern is to establish an international standard of their own and to arrest public misconceptions of PL marking versus powered emergency lighting.
Photoluminescent systems are non-radioactive materials containing pigments that store energy from natural and artificial lights. When the lights are extinguished, the materials glow in the dark by releasing this stored energy.
New Designs
The new PL (after-glowing) materials employ rare earth-borne pigments of heavy metals such as stronium, barium, europium, boron, arsenic, mercury and cadmium. Compared to conventional zinc sulphide PL the visible after-glow persist for 3 days rather than 5 hrs, and the 60 min luminance requirement is surpassed 10-20 times.25-35 min strip widths may be as effective as conventional 60-100 min strips. The IMO and DIN standards is yet to be 'upgraded'.
The new PL comes along with new product designs such as afterglowing handrails for use in utility service tunnels or complex industry structures. The PL material is moulded in special resins to withstand harsh environments. At least one manufacturer offer a 5 year warranty for offshore applications. They may be embedded in situ to decks of concrete protected by thermosetting top layers against impact from vehicles or tools. Some lacks the dreaded PVC.
They are UV-stable and may be used in sunlight.
Improvements ADD Substantial Safety Margins to Underrated PL
PL marking has been a trusted concept to provide reliable wayfinding in industry for decades. At the start of the 90-ies researchers in Norway tested the performance of PL in smoky conditions against powered lighting concepts. It was proven that despite the relatively low afterglowing luminance PL was capable of outperforming their high luminance electrically powered counterparts in the most severe smoke density.
The key factor is the short viewing distance provided by linear - also referred to as 'proximity', 'delineation' or 'continuous' marking. Strips of PL material identifies the escape route or rescue items located at floor, skirting boards, threads or handrails ('low location lighting') ensuring that the viewing distance of evacuees never exceed roughly one meter when they are bending slightly forward. Within this viewing range luminance is no longer important provided a visible contrast only. Indeed, added luminance may cause glaring and diffusion effects in smoke making visibility worse.
There was but one difficult shortcoming of zinc sulphide PL: Luminance was just barely sufficent at extreme smoke densities where they left no margins for upright evacuees looking at floor markings or for the visually impaired. Conventional wisdom stated 'the more luminance the better' and many therefore mistakenly preferred electrified lighting.
