On March 8, 2000, a subway accident took place in Tokyo. Trains derailed, six people were killed and sixty injured. If this accident had taken place in a tunnel instead of an open area, these numbers would certainly have been much higher. It is easy to imagine the panic caused if the accident victims were unable to determine the correct direction to evacuate the scene. In such situations, it would be very helpful if Glow-in-the-dark signs were installed in tunnels to show passengers the direction and distance to the nearest station.
This phosphorescent Evacuation Route Guiding Sign
directs potential accident victims to the nearest station.
Recently such phosphorescent signs were installed in a tunnel on the Nanboku line subway in Tokyo. The 30 x 60cm signs are made using a special grade phosphorescent pigment, which does not need any exclusive lighting apparatus for excitation. The light leaking from the windows of the passing trains is enough to activate these signs. After the successful field test on this subway line, it is expected that these signs will also be installed in other lines currently under construction.
Glow-in-the-dark signs are helpful not only for subways but also for other underground areas such as shopping malls, underground passages, and basements in the event of a blackout. Therefore the installation of Glow-in-the-dark signs is regulated by fire safety law.
The Fire Fighting Agency’s 1988 guidelines regarding “Exit signs and Evacuation route guiding signs” specified that the:
“Installation of emergency signs made of phosphorescent materials is recommended since they emit light even in the dark. Such signs should conform to JIS Z 9100 (Phosphorescent signs) and JIS Z 9115 (Self-luminous signs)”
This JIS standard for phosphorescent signs was recently revised because of the drastic increase in the afterglow intensities obtainable when using phosphorescent pigments, and the new Phosphorescent Safety Signs has replaced the old specification.
Table: Afterglow luminance of phosphorescent floor proximity markings (mcd/m2)
Type of photo-luminescent material Time (Min.)
0 30 60 90 120 150
AT20 13.7 3.8 3.0 2.7 2.5 2.4
ZnS 14.7 1.6 1.1 0.9 0.8 0.7
Excited with 25lux incandescent lamp for 30 minutes
Measuring conditions; measuring angle – 33 degrees, at a distance of 206cm
As shown in the above table, the new standard afterglow values are five to six times higher.
European safety signs
Photo; Examples of European safety signs
As far as international standards are concerned, ISO/FDIS 15370 1(Evacuation route guiding signs on passenger ships) regulates that the width of the evacuation pass markings can be reduced down to 25mm from the conventional 75mm (using ZnS based pigment). ISO/CD 17398 2(Safety signs) is currently under discussion for a revision taking this new JIS as a reference.
Phosphorescent material usage in European countries for fire safety signage has the highest utilization in the world. Approximately 100 metric tons per year of Phosphorescent pigment for sheet products is used. Many European sheet manufacturers have already begun to shift their production to high performance.
Emission spectrum of halogen lamp
Do highway tunnels not require phosphorescent signs? Under normal conditions, light is not of concern because of tunnel electrical lighting and headlights of the vehicles using it. However, should an accident or an electrical malfunction occur, tunnel lighting could become a problem. Phosphorescent materials that are effectively excited by headlights would be very helpful for use in highway tunnels. Unfortunately, modern headlights are equipped with halogen lamps. As shown in the above figure, their emission spectrum is not rich in the UV that is the most effective for the excitation. In order to solve this problem, LUMINTEC. were successful in developing a new version which can be excited by halogen lamps. The phosphorescent features of this new grade are shown in the table below.
Table; Comparison of new type with regular type.
After: 1min 5min 10min 20min 30min
Regular 100 100 100 100 100
New type 336 235 214 180 180
Excitation conditions: 600 lux (two 55watt halogen type headlights at 5meters for 30seconds)
The development of this new type has enabled LUMINTEC. to produce phosphorescent signs not only for highway tunnels but also for roads where ambient lighting is not present. This new version will be useful for accident prevention on rural roads or similar places where only headlights are available for excitation of the safety signage.