Note: Descriptions are shown in the official language in which they were submitted.
~l2~ 379
LIGHTING SYSTEM FOR HAZARDOUS AREAS
The present invention relates to the general
field of illumination. More specifically, the present
invention relates to illumination of areas containing
potentially explosive agents which can be in the form
o~ dust, vapor or gas.
Xllumination of an area containing a
potentially explosive agent can be complicated,
particularly if the area is quite large and/or a
variety of potentially explosive agents may be present.
An example of such an area is a hanger for painting
commercial aircraft, although similar problems are
present in various other areas classified as hazardous~
One approach has been simply to avold
placement of electric lighting equipment in a very
hazardous area (Class 1~ Division 1l in the terminology
of the National Electric Code) which can be achleved by
isolating the area containing thé potentially explosive
agent from the lighting equlpment. For example, ligbt
can be beamed through windows or transparent panels
from a nonhazardous location. In a large open area,
the lighting equipment may be placed at a locatlon
remote from the source of the potentially explosive
agent with increased ventilation to decrease the
possibility of ignition or explosion~
I~ the electric lighting equipment must be
place.d in the very hazardous area, the conventional
solution is to provide lighting fixtures class1fied as
"explosion-proof". Examples of such fixtures are shown
in Appleton et alO U.5. patent No. 3,675,007, issued
July 4, 1972, and Lowndes U.S. patent No. 4,142,179,
~h
7~
issued February 27, 1979. Such fixtures are not
intended to be airtight. Rather, conventional
explosion-proof lighting fixtures are designed and
located so that the maximum temperature of all exposed
parts of the fixtures does not exceed 80 pPrcent of the
ignition temperature of l:he explo~ive agent present.
Recoynizing that a malfunction may occur, such fixtures
are designed to withstand an internal explosion and
allow pressure to be released, such as by escape of
burned gases, but at temper~tures suf~iciently low that
external ignition is avoided.
Explosion-proof fixtures are very expensive
and may re~uire expensive maintenance and replacement
if used in a very hazardous area. In addition, the
limitation as to the external temperature still limits
the areas in which the fixtures can be used.
It is an object of the present invention to
provide a system for illuminating a hazardous area
safely by electric lighting fixtures.
It also is an object to provide such a system
in which the fixtures can be located in the hazardous
area close to the source of a potentially explosive
agent.
An additional object is to provide such a
system utilizing conventional heavy-duty fixtures with
a minimum of modi~ication, i.e., fixtures which are not
necessarily explosion-proof~
Another object is to provide such a system
adaptable to prevent buildup of potentlally explosive
agents on the fixture~
A further object is to provide such a system
effective for illuminating a large area which may
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contain a variety of po~entially explosive agents such
as a hanger for paintin~ commercial aircraft.
In accordance with the present invention,
aspects of the foregoing objects are acc~nplished by
providing a lighting system for an area classified as
hazardous by reason of possible presence of potentially
exp~osivQ a~ents in the ~mbie~t atmosphere,. said system
comprising a plurality of separate liyhtiny fixtures
disposed in such ambient atmosphere~ each of said
fixtures having an internal light-producing electric
lamp element and a substantially closed lamp housing
separate and spaced from the housings of the other
fixture, means for supplying clean, dry, nonambient gas,
under pressure which nonambient gas is devoid of the
potentially explosive agents, a network of closed
conduits extending from said supplying means, said
conduits having portions extending through such ambient
atmosphere to said fixtures/ respectively, and having
unobstructed interior passages in open communication
: 20 with the interiors of the housings of all of said
fixtures for supplying the clean r dry, nonambient gas
under pressure into said fixture housings, and means
~ for regulating the flow of the nonambient gas u~der
: pressure from said supplyih~ means into said conduit
network for controlling the supply of such nonambien~
gas to all o said housings of all of said fixtures.
Aspects of su~h objects also can be
- accomplished by the process of lighting an area
classified as hazardous by reason of possible presence
of potentially explosive agents in the ambient
atmosphere which comprlses disposing in such ambient
atmosphere a plurality o~ separate lighting fixtures
3~
each having an internal light-producing electxic lamp
element and a substantially closed lamp housing
separate and spaced from the housings of the other
fixtures, interconnecting such fixtures with a network
of closed conduits extending from a source of clean,
dry, nonambient gas under pressure which nonambient gas
is devoid of the potent:ially explosive agents, such
conduits having unobstnlcted interior passages in open
communication with the :interiors of the housings of all
of the fixtures for supplying the clean, dry,
nonambiant gas under pressure into the fixture
housings, and regulating the flow of the nonambient gas
under pressure from such source into the conduit
network for controlling the supply of such nonambient
gas to all of the housings of all of the fixtures.
In drawings which illustrate the preferred
embodiment of the invention:
Figure 1 is a top perspective of an electric
light fixture modified in accordance with the present
invention for use in a lighting system for hazardous
areas,
Figure 2 is a somewhat diagrammatic rear
elevation of the upper portion of the light~ng fixture
of Figure 1 J with parts Droken away,
Figure 3 is an enlarged section along line
3--3 of Figure 2 showing, in cros~ section, a condult
of a t:ype usable ln the invention,
Figure 3A is a corresponding section of a
- . modif:Led conduit or cable,
Fiyure 4 is a~somewhat diagrammatic side
eleval:ion of the upper portion of the light fixture of
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Figure 1, with parts broken away and parts shown in
section,
Figure 5 is an enlarged section along line
5~-5 of Figure 4, and
Figure 6 is a schematic diagram of the gas
supply system of a lighting system for hazardous axeas
in accoxdanc~ with ~he present invention.
A representative light fixture 1 of a type
usable in a lighting system for hazardous areas in
accordance with the present invention is illustrated i~
Figure 1. Most component.s of such fixture 1 correspond
to the "MF-HAZ" floodlight available from Wide-Lite of
San Marcos, Texas. With slight modifications, the less
expensive "F Series" floodlights available from the
same company can be used. The MF~HAZ floodlight is
approved for use in some hazardous locations, whereas
the F Series floodlight is not. Both of such
floodlights are designed to be substantially
weatherproof and include a substantially airtight lamp
housing 2, but neither is an explosion-proof fixture
approved for use in the most hazardous areas (Class 1,
Division 1).
The fixture housing ~ contains the lamp 3 and
rear reflector 4 and has a transparent front lens 5.
In a representative installation, the housing is
mounted on adjustable yohe arms 6 supported from a
ballast casing assembly 7. Such casing assembly, in
turn, is mounted on a lony upright cylindrical mast 8
extending upward from a heavy base 9.
With reference to Figure 2, power to the
fixture is conveyed by w.ires 10 extending through a
sealed or "sealtight" conduit 11. Such wires extend
~2~35~'C~
into the ballast casing 7 which includes among other
things the ballast capacitor 12 acc~ssible by a
removable access plate 13. The bottom portion of
casing 7 is hollow. Power to the lamp is conveyed by
wires 14 extending from inside the casing 7 through a
conduit 15 identical to the conduit 11. As seen in
Figure 3, conduit 15 is substantially oversized as
compared to the size of the wires 14, as is conduit 11
as compared to the size of wires 10~ When conventional
electrical conduit is used, preferably at least the
major portion of the cro,ss-sectional internal area of
each conduit is open and unobstructedO
In the MF-HAZ ~loodlight, the line from the
ballast casing to the larlp housing is a sealtight
conduit of the type used in the present invention,
whereas the wires 10 leading to the casing would
normally be encapsulated in a closed cable. In
accordance with the present invention, such a closed
cable is replaced by the oversized hollow conduit 11 to
allow unrestricted flow o~ nonexplosive gas such as
clean air through such conduit. From conduit 11, the
gas flows through the hollow interior of the ballast
casing 7 and conduit 15 into the lamp housing 2 as
represented by the arrows in Figure 2.
As best seen in Figure 5, conduit 15 is
sealed to the bottom lamp socket extension 16 o~ the
lamp housing 2. Such extension 16 is detachable from
the remainder of the housing for replacement of the
lamp 3~ There is an unobstructed passage from the
interior of conduit 15 alongslde the wires 14 to the
lamp socket 17 and outward from such socket through
slots 18. Gas passlng throuyh the slots 18 flows
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upward through the generally central hole 19 in the
bottom of the lamp housing 2 into the upper portion of
the housing.
As noted above, the particular fixtures
illustrated are designed to be essentially
weathertight. Such fixtures have sealed and gasketed
connections and joints. In accordance with the present
inventlon, one or more outlets 20 are provlded for the
gas flowing into the fixture. In the lllustrated
embodiment, two outlets 20 extend through the top of
the fixture housing 2 and lead to a long manifold Z1
extending along the upper leading edge of the housing
adjacent to the upper ed~Je of the transparent lens 5,
as best seen in Figure 1. Such manifold has a row of
closely spaced openings or holes 22 positioned such
~ that the gas leaves the manifold as a substantially
; continuous curtain blown down along the exterior of the
~-~ lens 5. In addition, or alternatively, openings can be
positioned to discharge gas rearward along the top of
the housing 2 which has beat-dissipating fins 23 to
assist in cooling the top surface of the housing.
Typically, the area immedlately above and surrounding
the upper portion of the lamp 1s the hottest portion of
the fixture and could Limit the specific hazardous
areas in which the fixture can be used. Blowing air
over the lens and/ox along the top of the hou6ing also
helps prevent buildup of potentially explosive agents
or agents which could interfer~e with light transmission
throuclh the lens, such 2-S paint spray. Buildup on~the
lens can itself increase the danger by absorbing heat
and increasing the surface temperature.
With reference to Figure 6, air to be
injected through a plurality of the ~ixtures can be
from the source of "factory air" at a manufacturing
location such as through a line 25. Preferably, a
manually valve 26 is supplied allowing the supply of
air to be close~ such as for maintenance to the entlre
sy~m Wl~h valv~ 26 in its normall~ open co~itio~
illustrated, the air flows to a normally open solenoid
valve 27 controlled at a central station such as by
conventional electromechanical controls or a
microprocessor 28. A pressure gauge 29 can be provided
to monitor the pressure of alr supplied.
Typically, factory air is ~uite dirty and may
be humid. For use in the present invention, it is
important that the air be clean so that particulates do
not collect in or clog any part of the system. Such
air also should be dry so that the electrical
connections are not exposed to moisture. One or more
conventional components 30 can be provided to clean and
dry the factory air. Also~ to protect the system in
case of a ~substantial overpressure condition, a
- conventional pressure~relief valve 32 can be used.
From valve 32l the supply line 25 branches to
lines 25' each of which leads to a n~twork of fixtures
-` 1 and has a pressure-reduction valve 33. Typically,
factory air is at fairly high pressure, such as 100
psi, whereas in accordance with the present invention
the clean air is supplied to the fixture at low or
moderate pressure, such as 2 or 3 psi above atmospheric
pressure. In each bxanch 25', the air supply line
extends from the reduction valve 33 to a conventional
rotamGter 34 to lndicate the flow rate and, if desired,
'
provide a signal indicative the flow rate to the
microprocessor 28. Downstream of the rotameter is an
additional pressure gauge 35 which, like gauge 29, also
can supply a signal to the microprocessor. In each
branch 25' leading to the individual light fixtures 1,
an additional solenoid valve 36 is used, preferably
controlled by the microprocessor 28, and an additional
man~al valve 31 is provided to be closed, for example,
if only one branch of the lighting system requires
maintenance.
Preferably, all of the air supply components
described above are located in the nonhazardous area NH
which, for the purposes of illustration, is indicated
to be to the left of a wall W in Figure 6, as compared
to the ha~ardous area H to the right of such wall. The
branch supply lines 25' hzve externally sealed joints
or fittings 37 as they extend from the nonhazardous
area to the hazardous area.
Within the haz2rdous area, preferably the air
is supplied through the same network of conduits 40 and
junction boxes 41 used for the power supply and control
wiring~ The electrical conduits 40 have ioints or
fittings 38 which are externally and internally sealed
as the conduits enter the hazardous area and the air
supply lines are in communicat1on with such conduits
through tee fittings 39. The junction boxes 41
preferably are~substalltially oversized to act as
pressure accumulatorsO From each junction box, a
single conduit 15 leads to the ballast casing for the
fixture 1, and in each interconnected line of fixtures,
preferably at least one ~unction box 41' contains a
pressure sensor and/or rotameter provldlng a signal to
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the control mechanism or microprocessor 28. In the
event of a substantial 10.5s of pressure or a serious
overpressure condition, bhe supply of electricity to
all Eixtuxes within the same branch is automatically
cut off, such as by autonatically opening a switch 42
in the primary power supply line. Within each branch
individual fixtures or banks of fixtures can be
controlled by manual switches in series with the
appropriate switch 42.
Preferably, thle control mechanism or
microprocessor 28 also monitors operation of the light
fixtures 1 at start-up or restart. Prior to actuation
of the lampsl airflow through the fixtures should be
sufficient to purge them of any potentially explosive
agents which may~have leaked into the fixtures. The
supply of air through the fixtures can be monitored
automatically so that the lamps can be actuated only
after a certain period has passed or a certain volume
of air has been injected throu~h the appropriate
,
branch, at which time the primary power supply switch
~ ~ or switches 42 can be closed automatically.
- In a permanent instalIation where the
positions of the fixtures will not change, the network
of standard electrical c~nduits can be used~ For a
portable lightlng system, however, it may be desirable
to provide the modified ~onduit-cable 43 illustrated in
Figure 3A. Such cable has a central unobstructed hose
44 with the power supply and control wires 45
encapsulated in insulative but preferably somewhat
flexibla material 46 such as a natural or synthetic
rubber which protects the wires and central hose from
kinks and breakage, even if the cable ~s moved and
~2~tg~
flexed frequently. In most installations, clean and
dry air is an acceptable pressurizing and purging
medium injected through the hose 44, but in extremely
hazardous conditions, inert gas can be used.
With reference to Figure 6, as an alternative
to a system in which gas is continuously injected into
and exhausted ~rom each individual fixture 1, each
fixture can be provided with a valve 47, diagrammati-
cally indicated in broklen lines in Figure 6, controlled
remotely such as by the microprocessor 280 At start-up
or restart, the primary pol.~er supply switches 42 woul~
be opened and all of the valves 47 would be opened
while the system is purged of any possible potentially
explosive agents. ~fter a predetermined period or
~;~ amount of purging airflow through the system, the
valYes 47 can be closed automatically to pressurize the
substantially sealed fixtures 1 and thereby prevent
introduction of potentially explosive agents into the
,
fixtures. As in the pre~iously described embodiment,
the pressure of the systPm can be monitored
automatically by the control mechanism or
microprocessor 28 to cut off the supply of electric
power automatically if the pressure is danyerously
reduced or increased above design conditions.
Another option lS to actuate valves 47 to
full open positions for ~laximum flow at start-up and
restaxt and to close such valves partially after the
system is purged to a desired degree for continuous but
decreased flow of nonexplosiYe gas under normal
operating conditions.
Still another option is to increase the
pressure of nonexplosive gas supplied to the system at
1 1
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start-up or restart for a corresponding increase in the
purging gas flow. With reference to the broken line
illustration toward the left of the upper branch 26' in
Figure 6, a second reduc~.ion valve 33' can be
connection in parallel wi.th valve 33 and in series with
a second solenoid valve 36'. At start-up or restart,
valve 36' can be opened automati~ally ~o supply gas to
reduction valve 23~ in addition to the supply to valve
33. Valve 33' can xeduce the pressure of nonexploslve
gas to a lesser degree than valve 33, such as 5 to 10
psi above atmospheric pressure. After the desired
degree of purging has occurred, the control mechanism
~: or microprocessor 28 can automatically close solenoid
valve 36', so that during normal operating conditions
all of the nonexplosive gas is fed through reduction
valve 33.
In either system~ fixtures which are not
necessarily explosion-proof can be used, such as
substantially sealed heavy-duty fixtures, and the
fixtures can be safely located in the hazardous area,
even close to the source of a potentially explosive
agent. Consequently, thP system ln accordance wlth the
present invention is adaptable for previously difficult
illumination problems such as to provide bright
illumination in a paint hanger- for commercial aircraft
at hard to light locations such as by beaming light
from close to the floor underneath the wings and b~dy
of the aircraft.
