High intensity discharge lighting is used extensively in areas such as
school gymnasiums, vocational shops and other high-bay areas. Metal halide,
mercury vapor, and high pressure sodium HID lighting are commonly used, with
metal halide being the lamp of choice because of energy efficiency and light
color. Unfortunately, metal halide lamps have the potential to fail
non-passively, which means they can explode. Another problem is that UV
(ultraviolet) radiation can sometimes be emitted if a lamp outer jacket shatters
or is cracked. Overexposure to UV radiation may cause skin and eye irritations.
To minimize possible safety problems with HID lighting (primarily metal halide),
the following is recommended.
- Fixtures need to be checked to see if lamps are open types or are
protected by the design of the fixture. With open types of fixtures, lamps
are exposed directly to lighted area without any containment lens, which
would prevent problems with exposure to UV or possible injuries that could
result from a lamp that explodes. If protected, the lamps should be enclosed
with a lens made of acrylic or polycarbonate, depending on design.
- If a lamp is protected (enclosed), it should be marked on the fixture
that it meets UL-1598 standard. This will ensure that if an explosion
occurs or if a lamp becomes broken that fire hazards associated with
explosions or UV associated with a broken lamp will be contained to the
fixture. Usually, in areas such as gymnasiums, protective lens is furnished
as a part of fixture. The new metal halide lamp fixtures 250 watts and below
are required to be enclosed so they are protected. Areas such as gymnasiums
generally use 400 watts or larger fixtures. These fixtures may or may not
have a protective lens.
- If you determine that your school has open metal halide fixtures, a
more expensive lamp that is self-extinguishing (will burn out quickly if
lamp is cracked or broken) is available. It will protect from both explosion
of the arc portion of the lamp and will cause the lamp to fail before
excessive exposure to UV is possible. These special lamps will be designated
with an "O" rating from the manufacturer, which indicates
that the lamp arc tube has been enclosed with an additional protective glass
shroud.
- Other HID (high intensity discharge) lamps, such a mercury vapor and
high pressure sodium, generally do not have the same problems with
explosions as metal halide. Mercury vapor lamps do have the UV exposure
risks and should be contained with a protective lens on the fixture.
- In areas such as gymnasiums where fixtures are subject to being hit by
balls, etc., it is better to use a cord-connected fixture with a safety
chain rather than a rigid mounting. This will cause less stress on lamps if
they are hit because the fixture will move, causing less shock to lamp.
- Consider group relamping – especially of metal halide lamps in
high bay areas such as gymnasiums. Metal halides have rated lives of
approximately 5,000 to 20,000 hours, depending on wattage. Light output of
lamps drops off quickly as lamp ages resulting in inefficiency. Some experts
indicate that group relamping of metal halides should occur at 50 to 70
percent of rated life. Group relamping tends to eliminate problems with lamp
explosions. Always follow manufacturers recommendations on lamps that can be
used with fixtures and requirement relative to how the lamp can be mounted
(vertical or horizontal, etc.).
In summary, check fixtures to determine whether they are open or enclosed
types. Talk with lighting representative on the method to upgrade if required.
Consider group relamping as outlined. On new work, ensure that safety
considerations are part of design process. If you need additional information,
please contact Bob Bryan, School Planning Section, North Carolina Department of
Public Instruction, at (919) 807-3564 or John Kuchnia, Plant Operation Section,
(919) 807-3548.