Risk Management Guidelines
Fire Hazards of High Intensity Discharge Lighting
Introduction
High Intensity Discharge (HID) lighting
systems have been used for many years
internally, in factories and warehouses, and
externally, principally in street and security
lighting. They are increasingly common as
a light source and appear in many specialist
industries and equipment. HID lights have
a long life-span, up to 25,000 hours, and
give a wide coverage of efficient lighting.
They are gas filled tubes containing
mercury, argon and metal halides, usually
sodium iodide, scandium iodide and
occasionally lithium iodide. These gases
improve luminance and colour quality. The
lamps are denoted “M” on the bulb.
They use ballasts to produce light when an
electric current is passed between two
tungsten electrodes inside a gas filled
quartz or ceramic arc tube. This flow of
current creates an arc that vaporises the
metallic content in the tube. When
operated, the temperature [up to13000C]
and pressure [up to 6 bar in the case of
metal halide lamps, and 3.5 bar otherwise]
of the lamp rises, with a characteristic delay
of several minutes in developing the visible
light coming from the lamp. A hot lamp
cannot be re-started until it has cooled
down again. Bulb sizes range from
75Watts to 1500Watts.
Other types, which are mostly used
externally, are:
A variety of this light technology, known as
HMI, has a more intense arc, and are
generally used in spotlights.
a) Mercury Vapour lamps, which have
mercury sealed in an argon gas fill in
the quartz tube that emits a blue-white
visible light, and Ultra Violet invisible
light, that is corrected to a more natural
light by the addition of phosphors.
Unlike other types of Discharge lamps
they can work on DC as well as AC
current. They are denoted “H” on the
bulb.
b) High Pressure Sodium Vapour lamps
have an arc tube of ceramic
construction as at the high temperatures
associated with this type of light
(13000C) sodium chemically attacks
glass and quartz. Solid sodium and
mercury are sealed in the xenon (or
sometimes neon-argon) inert gas filled
arc tube within the outer glass
envelope. These produce an orange –
white light with the highest luminance
efficiency of all HID lights. These are
the only HID lights with starters, except
for “instant re-start” metal halide lamps.
They are denoted “S” on the bulb.
Whilst these lamps are both cost effective
and efficient, they also have been involved
in a number of fires over the years.
This Risk Management Guideline is aimed
at the prevention of such fires in buildings.
HID Technology
Metal Halide lamps are the type most
commonly installed inside buildings, and
can be 75% more efficient than fluorescent
lamps.
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Risk Management Guidelines
Failure Problems
Recommendations for Safe Use of
HID Lights
Failures, leading for fire and explosion, can
occur if:
Fit a shroud to protect the arc tube
where a lamp containment barrier is not
possible e.g. in the case of open
fixtures. The ANSI electrical safety
code designates “O” rating usually for
shrouded lamps suitable for use with
open fixtures.
a) the lamp is not positioned in accordance
with manufacturer‟s specifications.
b) a breakage occurs following impact, e.g.
from stock being positioned by fork lift
trucks.
c) a tube fails due to age or an incorrectly
rated tube or ballast being used. A
particular ballast will generally only work
effectively with one type of bulb. The
wattage of the bulb must always be
matched with the ballast. For instance,
if a smaller rated bulb is used than the
correct one it can easily overheat and
then explode. Conversely, if a larger
rated bulb is used it will have a
shortened lifetime but the ballast could
overheat because the bulb is not
warming to the correct temperature.
Where there are high values of goods,
and where particularly susceptible
goods such as packaging materials are
present, both a lamp containment
barrier, as part of the fixture and an “O”
rated lamp with a shroud fitted, are
strongly recommended.
New installations should have external
barriers that fully enclose the whole
lamp unit. “E” rated units must have
enclosed fixtures. There have been no
known incidents of fires caused by HID
lights fitted with non-combustible
enclosures.
d) the bulb „self cycles‟ i.e. may start
correctly and then turn off. This is
usually caused by a bad ballast or
overheating of the bulb with the result
that the protector shuts off the bulb.
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Only retrofit lamp containment barriers if
the action does not invalidate the
approved standard for the fixture
assembly. Always fit the correct bulb to
the correct ballast and power supply.
Remember that tempered or
borosilicate glass barriers are preferred
as normal glass could shatter. Plastic
and aluminium barriers could melt and
are not recommended.
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Risk Management Guidelines
Lamps must always be positioned in
accordance with the manufacturer‟s
requirements and must be clear of both
combustible building construction
materials as well as combustible goods.
The positioning of goods should take
account of the possible explosion and
descent of very hot materials from the
lamps. This is particularly important for
the higher temperature lights but less so
for low pressure sodium lights that can
be cooler than ordinary domestic
lighting.
Where the lamps are operated
continuously night and day it is required
that they are turned off for around 15
minutes each week. If there are
problems with the lamp it will not reignite after the “cycle-off” period and
should be replaced.
This will ensure that the fault has a
passive rather than violent reaction due
to the fault. The “cycle-off” process
reduces the potential for explosions in
operation.
Those checking lamps should only
handle them when they are cold and the
power is locked off.
The lamps should be changed after
70% of their rated life-span. They
should be regularly inspected, and if
found to be scratched or damaged in
any way, they should be changed. The
checks should also include looking for
signs of water ingress in the vicinity of
the light unit. This could result in
thermal shock and potential explosion.
Remember that lamp explosions can
seriously injure staff working in the area.
Full enclosures and the use of shrouds
are therefore strongly recommended
where there routinely exposure to the
workforce.
Fork-lift truck drivers should be trained
in the hazards of these lights and
should take care in storing and moving
goods nearby.
Generally lights should only changed by
qualified electricians and a safe means
of gaining access to height should
always be used.
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© 2010 Royal & Sun Alliance Insurance plc
Risk Management Guidelines
These and other Risk Management Guidelines addressing a wide variety of risk control issues
are freely available from: www.rsabroker.com/risk-management
The information set out in this document constitutes a set of general guidelines and
should not be construed or relied upon as specialist advice. RSA does not guarantee
that all hazards and exposures relating to the subject matter of this document are
covered. Therefore RSA accepts no responsibility towards any person relying upon
these Risk Management Guidelines nor accepts any liability whatsoever for the accuracy
of data supplied by another party or the consequences of reliance upon it.
Royal & Sun Alliance Insurance plc (No. 93792).
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