by John M. Harder
Guiding occupants out of a smoke-filled or darkened building via luminescing egress demarcation could save lives in an emergency. Specifying photoluminescent (PL) egress products in commercial buildings is required by building codes, but should also be done with care to ensure the selected materials provide durability and long-term performance. Doing so could mean the difference between life or death for occupants exiting a facility during a fire, power outage, or other catastrophe.
PL systems are now considered critical components in an effective egress system. While emergency electrical lighting has long been a staple of facility life-safety systems, it is not failsafe since a catastrophe can potentially interrupt its link to the emergency power supply. In contrast, PL stair nosings, pathway markings, and exit signs and demarcation are not subject to power outages. Instead, they rely on PL pigmentation charged by natural or artificial light sources, such as sunlight, fluorescent, incandescent, and light-emitting diode (LED) fixtures. The charge allows the pigments to instantaneously glow bright enough to lead occupants out of a facility when electric or natural light sources fail.
The PL pigments consist of crystals charged by storing light photons when exposed to natural or artificial light. Once charged, the energy stored in the crystals slowly exhausts until it is completely depleted. This slow release allows products using the pigment to emit light for extended periods of time. The material is continually recharged by exposing it to a light source.
Pigment technology has become so advanced some industry studies suggest it can potentially be employed as an alternative to the more expensive emergency electrical lighting egress systems. (For more, read “Literature Review on Photoluminescent Material Used as a Safety Wayguidance System” by R. Tonikian, G. Proulx, N. Bénichou, and I. Reid, and published by The National Research Council Canada [NRC].)
Advancements in PL technology
The notion PL products might someday qualify as an emergency electric lighting alternative demonstrates the technology has come a long way. Most modern PL products use the patented phosphorescent chemical, strontium aluminate oxide. It is 10 times brighter, and lasts 10 times longer than its predecessor, copper-activated zinc sulfide (ZnS), which was the convention of PL 25 years ago.
The glow duration and brightness of PL products depend on the length and intensity of the light exposure. For this reason, the International Building Code (IBC) has adopted two test standards to set the bar for performance of PL products in egress applications. Products must meet either Underwriters Laboratories (UL) 1994, Luminous Egress Path-marking Systems, or ASTM E2072, Standard Specification for Photoluminescent (Phosphorescent) Safety Markings. These standards dictate the brightness and exposure time of the charging light, the decay time once the charging light is removed, and the performance expectations of the product at the end of this time. Both standards require a 60-minute exposure to an 11-lux (1-footcandle) light source and a 90-minute decay time. However, they differ in how they measure performance. UL 1994 requires the markings to be distinguishable from a defined distance, while ASTM mandates a specific luminance reading at particular time intervals. These tests recreate the potential low-light conditions in the stairwell corners.
|CODES FOR PHOTOLUMINESCENT EGRESS|
|Important building code sections requiring photoluminescent (PL) exit path markings are:
Photoluminescent stairway identification signs shall be included in interior exit stairways. This is effective from January 2009.
Photoluminescent markings shall be provided in interior exit stairways of building types A, B, E, I, M, and R-1. This section became effective in January 2009.
Effective from January 2009, the section makes photoluminescent exit stair path markings optional for all buildings, new and existing, regardless of height.
Required in occupancies in exit corridors leading to emergency exit stairwells. This was made effective in January 2008.
Required in all new and existing buildings, and effective from March 2005.