Long gone are the times when we thought of photoluminescent material as gimmick glow-in-the-dark Halloween stuff. These days, photoluminescent safety markings are required by codes and controlled by standards in the United States and worldwide. Photoluminescent material is divided into two categories:
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- Safety markings.
- Exit signs.
How it works
The composition of both categories is the same: photoluminescent pigments in a base material (paint, film or rigid sheeting for tape and signs, and various plastics for extrusion and injection molding). The pigments absorb energy from daylight and artificial fluorescent and incandescent lighting. In full darkness, the photoluminescent effect is visible as a yellowish to green-yellowish glow that declines over time. How visible a material is in full darkness depends on several factors.
First is the pigment type. Zinc sulfide has the advantage in that it charges quickly even in dim ambient light, but its glow declines faster than that of other materials. With sufficient pigment loading, zinc sulfide can provide as much as eight hours of luminance.
Short charging time may be important in locations that use motion-detectors, which only activate when something in the area moves. Products based on zinc sulfide may be ideal in dimly lit areas or in storage rooms where the lights are on only when someone enters. In sudden darkness conditions, the zinc sulfide-based safety markings have the best chance of being sufficiently charged to provide light.
Strontium-oxide aluminate pigment glows for many hours, even days, but it requires bright activating light to achieve a sufficient chargeincandescent bulbs are too dimand requires a charging time of at least an hour for good output.
The second factor affecting output is the type of activating light source. Sunlight and fluorescent lighting are good activators. Soft, warm incandescent light bulbs only provide limited activation, while red light or sodium vapor light won't activate the pigments at all.
Third is the level of illumination on marking surface. The more activating light that shines on the surface, the brighter the material will be in full darkness. One foot-candle (10 lux) is the bare minimum illumination level that will serve the purpose.
The fourth factor is the duration of activation. A zinc-sulfide-based marking may be sufficiently charged after five to 10 minutes of fluorescent activation, whereas a strontium-aluminate-based marking may need more than an hour to acquire a sufficient charge.
Testing for sufficient charge
The best way to test is to use a light meter that measures the activating light levels in foot-candles and lux. Light meters are available for rent. Another possibility is to conduct an empirical test. Install the product, charge it, turn off the lights and try to find your way out.
When the lights go out, safety markings define the best escape route.
Marking escape routes
Photoluminescent safety markings outline escape routes from the place of occupancy inside a building to safe areas outside. The American Society for Testing and Materials (ASTM) publishes three relevant standards:
E 2072-00 Standard Specification for Photoluminescent (Phosphorescent) Safety Markings.
E 2073-02 Standard Test Method for Photopic Luminance of Photoluminescent (Phosphorescent) Markings.
E 2030-02 Standard Guide for Recommended Uses of Photoluminescent (Phosphorescent) Safety Markings.
The standard specification sets minimum acceptable levels of luminance. If a marking of a certain width meets or exceeds the luminance requirements, it qualifies for use in safety installations. Otherwise, it's only suitable for gimmick or novelty applications.
The standard test method describes how to prepare a product for testing, apply suitable instruments and record the luminance findings for repeatable and reproducible test results for the purpose of comparing products.
The standard guide describes recommended uses with informative drawings highlighting the installation of photoluminescent safety markings. The markings are typically located low, either directly on the floor or on the wall within eight inches of the floor. During a building fire, smoke accumulates under the ceiling and quickly obscures electrical lighting. Building occupants are forced to crawl below a layer of heavy smoke. Photoluminescent lighting in low locations outlines the escape path. The floor markings may be anti-skid tape, epoxy floor paint or durable floor inserts that resist the wear and tear of foot traffic.
To avoid injuries, obstacles and protrusions are marked with a glowing warning tape, acrylic wall paint or cushioned bumper guards. Exit doorframes are outlined with tape or paint. Photoluminescent material is placed on or behind the exit door handle to avoid searching for the door's opening device. One photoluminescent exit sign should be installed above the door to be visible during clear air evacuation. A second exit sign should be in a low location to be visible underneath a smoke layer.
In staircases, each step should be marked at one or more locationson the left, on the right and along the front edge of each stair tread. A line should lead from one flight of stairs along the landing to the next flight of stairs. The handrail should be marked to provide additional guidance. "No Re-entry" doors should be marked with a continuous line (the door frame doesn't get highlighted), and a photoluminescent sign at eye level should indicate the nearest re-entry floor. The doorframe and door handle of the exit door leading out of the staircase should be marked and a "Re-entry on This Floor" sign mounted on the door.
Fire fighting equipment and other life safety installations, such as first aid kits and defibrillators, should be marked with photoluminescent warning tape and glowing signage.
In industrial facilities, photoluminescent markings point out escape routes along aisles of shelves, around stacks of pallets and machinery, along catwalks and on stairs from a mezzanine. Durable porcelain-enamel coated floor inserts or indoor pavement markers that resist forklift traffic should lead workers to the exits.
Unfortunately, most building occupants never take notice of building escape route maps during non-emergency situations. Only when disaster strikes do they realize the importance of the maps. At that point, however, nobody can read them, as they are commonly printed on paper not visible in the dark. Photoluminescent escape route maps should be printed on a clear film backed by a photoluminescent rigid panel, and the two layers should be mounted in a frame. Should the power fail, this escape route map remains visible in full darkness and helps building occupants escape.
Mark each tread on stairways and mark landings.
High performance exit signs
The National Fire Protection Association's 2001 edition of NFPA 101Life Safety Code allows the use of photoluminescent exit signs if they are in compliance with Underwriters Laboratories Inc.'s UL924 Standard for Emergency Lighting and Power Equipment.
In July 2001, Underwriters Laboratories updated its Standard UL924 by including test requirements for photoluminescent exit signs. The signs must pass a mold stress relief test, a humidity exposure test, an impact test and a visibility test.
For the latter test, photoluminescent signs with the correct spelling "EXIT" and the incorrect spelling "FYIT" are exposed to five foot-candles of fluorescent lighting for sixty minutes. Then they are kept in full darkness for 90 minutes. Then eight observers from four age groups, ranging from 18 to 70, test the legibility of the two signs at a viewing distance of 50 feet, 75 feet or 100 feet. If observers can read the respective texts correctly and quickly, the signs are eligible for the UL924-listing.
The front of UL924-listed photoluminescent exit signs must display two important messages:
Its viewing distance (50 feet or 75 feet). The 100-foot-viewing distance doesn't need to be printed, as that is the standard distance.
A notice that whenever the building is occupied, the sign must be illuminated by a minimum of five foot-candles (54 lux) of fluorescent lighting.
OSHA's Occupational Safety and Health Standard, Part 1910.37 for Exit Routes, requires exit signs to be distinctive in color and illuminated by at least five foot-candles (54 lux) from a reliable light source. High performance photoluminescent exit signs fulfill these requirements.
Sometimes it's difficult for users to differentiate between a self-luminous sign and a photoluminescent sign. "Self-luminous" is another term for radio-luminescent: These signs are filled with radioactive tritium gas, have a life expectancy of 10, 15 or 20 years and are to be treated as radioactive waste at their life's end. They can't be thrown into the trash, but must be returned to the manufacturer for proper recycling.
Photoluminescent exit signs, sometimes called self-illuminating, are non-radioactive and non-toxic. They often have a 25-year life expectancy rating (depending on brand) and can be disposed of normally as required by local regulations.
Don't wait until disaster strikes
During the 1993 World Trade Center terrorist bomb attack, smoke quickly rose up the emergency staircases. It took many building occupants hours to evacuate through the dense smoke. Following that event, the Port Authority of New York and New Jersey installed photoluminescent epoxy paint on each step, on each landing and on handrails. They also installed photoluminescent signage indicating the floor and staircase numbers, plus re-entry possibilities. These photoluminescent escape route markings were praised as aiding the evacuation during the September 11, 2001 events.
Since then, numerous building owners and facility managers have started requiring photoluminescent escape route markings in their facilities to increase the safety level. New requirements and regulations requiring photoluminescent signage and low location lighting are appearing in many jurisdictions.
Be proactive and install photoluminescent safety markings and exit signs in your facilities. You want to be well-equipped in case of a power failure or a dense-smoke fire.
Marina Batzke is Chairperson of ASTM Sub-committee E12.13 on Photoluminescent Safety Markings and general manager of American PERMALIGHT Inc., Torrance, Calif. She can be reached at (310) 891-0924 and email@example.com.