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MERCURY
VAPOR LAMPS
 Mercury
vapor lamps are widely used to light both indoor and outdoor
areas such as gymnasiums, factories, department stores, banks,
highways, parks and sports fields. These lamps are potential
emitters of ultraviolet radiation (UV). Mercury vapor lamps
consist of an inner arc discharge tube constructed of quartz
surrounded by an outer hard borasilicate glass envelope. Shortwave
UV, a result of the decay of mercury atom electrons from an
excited to a stable state, is readily transmitted through the
inner quartz tube but is virtually blocked by the outer glass
envelope during normal operation. Partial or total removal of
the outer envelope allows the shortwave UV radiation to emanate
from the lamp. In addition, the lamp may continue to operate
for several weeks with the outer protective glass envelope broken.
The resulting exposure to UV radiation from such a lamp causes
erythema (skin burns) and photokeratitis (inflammation of the
eye) which may lead to permanent eye damage. Extensive or repeated
exposure may lead to premature aging of the skin or skin cancer
in later years.
The
Food and Drug Administration's Safety Performance Standard for
mercury vapor lamps effective March 1980 (21 CFR 1040, Federal
Register Volume 44, No. 175, p. 52191) permits the manufacture
of two types of lamps. One type has a self-extinguishing device
that will shut the lamp off within 15 minutes after the outer
globe is broken. These lamps are marked "T". The following
label will appear on the packaging of self-extinguishing mercury
vapor lamps and metal halide lamps: "This lamp should
self-extinguish within 15 minutes after the outer envelope is
broken or punctured. If such damage occurs, TURN OFF AND REMOVE
LAMP to avoid possible injury from hazardous shortwave ultraviolet
radiation." It should be noted that a "self extinguishing"
lamp may take as long as 15 minutes to turn off after the outer
bulb has been broken. Therefore, if the lamp breaks, even if
it is self-extinguishing, people should leave the area immediately.
The
second type of mercury vapor lamp does not have a self-extinguishing
device incorporated into the lamp. This type of lamp should
only be used in a totally enclosed lighting fixture with a glass
or plastic shield that will absorb the hazardous UV radiation,
or in areas where people will not be exposed to UV radiation
if the outer globe is broken. These lamps are marked "R".
The following label must appear on the packaging and advertising
for non self-extinguishing mercury vapor and metal halide lamps:
"WARNING: This lamp can cause serious skin burns and
eye inflammation from shortwave ultraviolet radiation if the
outer envelope of the lamp is broken or punctured. Do not use
where people will remain for more than a few minutes unless
adequate shielding or other safety precautions are used. Lamps
that will automatically extinguish when the outer envelope is
broken or punctured are commercially available."
The
use of mercury vapor lamps in New Jersey is regulated under
N.J.A.C. 7:28-41, Mercury Vapor
Lamps. Requirements for the indoor use of mercury vapor
lamps can be found in N.J.A.C. 7:28-41.3(a). The requirements
state that for indoor use, the mercury vapor lamp must be of
the self-extinguishing type or if it is non-extinguishing, it
must be installed within a totally enclosed lighting fixture
with a protective shield which protects the lamp for damage
and absorbs shortwave UV radiation. Requirements for the outdoor
use of mercury vapor lamps can be found in N.J.A.C. 7:28-41.4(a).
If people are likely to remain in an outdoor area of illumination
for more than 15 minutes, the same provisions found in 41.3(a)
must be met. However, 7:28-41.4(b) states that the Department
may exempt certain outdoor installations from the provisions
of 41.4(a) if it determines that sufficient precautions have
been taken to minimize the possibility of overexposure to shortwave
UV radiation.
If you
have questions about this topic, try our Questions
and Answers.
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