United States Patent 15
`Betzvog, Jr.
`
`[11] Patent Number:
`(45) Date of Patent:
`
`4,937,717
`Jun. 26, 1990
`
`[54] LIGHTING SYSTEM FOR HAZARDOUS
`AREAS
`
`[76]
`
`Inventor:
`
`John M.Betzvog, Jr., 919 NW 56th,
`Seattle, Wash. 98107
`
`[21] Appl. No.: 204,465
`
`[22] Filed:
`
`Jun. 9, 1988
`
`[S51] Tt. Cho cosccssssssesecssescssssscesssenssseesee F21V 25/00
`[52] U.S. Che seesessssssssssssssssssssesseeessees 362/310; 362/264;
`362/294; 362/295; 362/276; 362/373
`[58] Field of Search ............... 362/264, 294, 295, 373,
`‘
`362/310, 267, 276; 174/47
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`3,112,890 12/1963 Snelling....
`.- 240/51.11
`
`3,217,097 11/1965 Pauli et al.
`....
`wee 174/47
`
`3,375,773 4/1968 Wotowiec etal. ..........sccssse 98/40
`3,675,007 7/1972 Appletonetal......
`. 240/11.2 E
`
`00.0...
`cesses 362/267
`3,754,133
`8/1973 Youdin et ab.
`
`3,959,644 5/1976 Dammeletal. ..
`seee 240/47
`
`4,142,179 2/1979 Lowndes .........sssssecersssseerere 340/321
`
`4,546,420 10/1985 Wheeler et al.
`..........cccseee 362/268
`
`4,630,182 12/1986 Moroiet ab.
`eee 362/294
`
`4,678,290 7/1987 Welker ..........
`.- 362/267
`
`4,701,833 10/1987 Bornhorst ........cscsscsscesssees 362/299
`FOREIGN PATENT DOCUMENTS
`529341
`3/1975 ULS.S.R. wnccscccssscccssscsessonnseee 362/294
`
`a» 362/294
`494562 2/1976 U.S.S.R..........
`
`575975 4/1976 United Kingdom................ 362/294
`
`OTHER PUBLICATIONS
`
`Crouse~Hinds 1987 Code Digest.
`NFPA 196 “Standard for Purged and Pressurized En-
`closures for Electrical Equipment”, 1986 Edition.
`Appleton NEC 1987 Code Review.
`Wide-Lite Hostile Environment Lighting Guide, no
`date.
`
`Primary Examiner—Stephen F. Husar
`Assistant Examiner-—-Sue Hagarman
`Attorney, Agent, or Firm—-Ward Brown; Robert W.
`Beach
`
`ABSTRACT
`[57]
`Conduits having the electric wiring for supplying
`powerto lighting fixtures in an area classified as hazard-
`ous by reason of the presence of potentially explosive
`dust, vapor or gas have unobstructed interior passages
`for conveying nonexplosive gas under pressure from
`outside the hazardous area to each fixture. The pressure
`of gas in the conduit network can be monitored auto-
`matically and control mechanism can be provided to
`shutoff the supply of electric powerto thefixtures if the
`pressure falls below a predetermined pressure or a dan-
`gerous over-pressure condition occurs. At each fixture,
`the nonexplosive gas can be discharged along the face
`of the transparent fixture lens and/or along an exterior
`surface of the fixture housing to prevent build-up of
`potentially explosive agents and to cool the housing.
`
`13 Ciaims, 4 Drawing Sheets
`
`
`
`
`Petitioner Ensign
`Exhibit 1026 - Page 1 of 9
`
`Petitioner Ensign
`Exhibit 1026 - Page 1 of 9
`
`

`

`US. Patent
`
`Jun.26,1990
`
`4,937,717
`
`Sheet 1of4
`
` WisanrNa*4 haoiON
`
`Exhibit£1026. Page2or9
`
`etitioner
`
`Ensiign
`
`Petitioner Ensign
`Exhibit 1026 - Page 2 of 9
`
`

`

`il a P
`
`yG
`yeVg
`
`etitioner Ensign
`Exhibit 1026 - Page 3 of 9
`
`
`
`US. Patent—Jun.26, 190 Sheet 2 of 4 4,937,717
`
`
`
`Petitioner Ensign
`Exhibit 1026 - Page 3 of 9
`
`

`

`
`
`US. Patent—Jun. 26, 1990 Sheet 30f4 4,937,717
`
`
`
`
`
`OleOCCCCaeplOSS
`
`adepddehehe
`
`
`
`
`
`Sy«
`
`
`
`Pagawa
`
`rr
`
`ia
`
`|>
`
`ar
`
`ets
`
`Petitioner Ensign
`Exhibit 1026 - Page 4 of 9
`
`Petitioner Ensign
`Exhibit 1026 - Page 4 of 9
`
`

`

`US. Patent
`
`Jun. 26, 1990
`
`Sheet 4 of 4
`
`4,937,717
`
`NH
`
`i
`
`“
`
`YO
`
`Ls
`
`7)
`
`i!
`
`‘
`4
`7
`}
`y H
`BZ
`
`
`on,
`4,
`\\
`B -
`W. y
`27
`K
`OnA |
`ael- --1 G we A,
`
`
`
`
`12 Y
`Tee
`T #
`r
`
`4 1
`47 SN
`ey) 42
`SF |
`
`y
`i
`BH On
`r Ee) Wy a
`36°
`ye aH
`i sors a
`IF
`2
`REDE ©)
`a Y
`OHO-S5
`a
`i
`Z
`——_ —
`7
`y
`42 36 Y
`Z
`y
`Y |
`j
`U
`
`°
`
`TUF.6.
`
`4
`
`V7
`
`fL Yo
`SCV
`
`h
`
`IS
`e¥
`
`LY,
`Ly
`4"
`mah
`47S.
`4/ 6 he”
`
`Pe
`
`¢
`
`‘\
`
`Petitioner Ensign
`Exhibit 1026 - Page 5 of 9
`
`Petitioner Ensign
`Exhibit 1026 - Page 5 of 9
`
`

`

`1
`
`4,937,717
`
`LIGHTING SYSTEM FOR HAZARDOUS AREAS
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`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 of dust, vapor
`or gas.
`2. Prior Art
`Illumination of an area containing a potentially explo-
`sive 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 areais a
`hangerfor painting commercial aircraft, although simi-
`lar problems are present in various otherareas classified
`as hazardous.
`Oneapproachhas been simply to avoid placement of
`electric lighting equipment in a very hazardous area
`(Class 1, Division 1, in the terminology of the National
`Electric Code) which can be achieved byisolating the
`area containing the potentially explosive agent from the
`lighting equipment. For example, light can be beamed
`through windowsortransparent panels from a nonhaz-
`ardous location. In a large open area, the lighting equip-
`_ment may be placed at a location remote from the
`source of the potentially explosive agent with increased
`ventilation to decrease the possibility of ignition or
`explosion.
`If the electric lighting equipment must be placed in
`the very hazardous area, the conventional solution is to
`providelighting fixtures classified as “explosion-proof”.
`Examples of such fixtures are shown in Appletonetal.
`U.S. Pat. No. 3,675,007,
`issued July 4, 1972, and
`Lowndes U.S. Pat. No. 4,142,179, issued Feb. 27, 1979.
`Such fixtures are not intended to be airtight. Rather,
`conventional explosion-proof lighting fixtures are de-
`signed and located so that the maximum temperature of
`all exposed parts of the fixtures does not exceed 80
`percent of the ignition temperature of the explosive
`agent present arid, recognizing that a malfunction may
`occur, such fixtures are designed to withstand an inter-
`nal explosion and allow pressure to be released, such as
`by escape of burned gases, but at temperatures suffi-
`ciently low that external ignition is avoided.
`Explosion-prooffixtures are very expensive and may
`require expensive maintenance and replacementif used
`in a very hazardous area. In addition, the limitation as to
`the external temperaturestill limits the areas in which
`the fixtures can be used.
`
`SUMMARYOF THE INVENTION
`
`It is an object of the present invention to provide a
`system for illuminating a hazardous area safely by elec-
`tric 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 uti-
`lizing conventional heavy-duty fixtures with a mini-
`mum of modification,i.e., fixtures which are not neces-
`sarily explosion-proof.
`Anotherobject is to provide such a system adaptable
`to prevent buildup of potentially explosive agents on
`the fixture.
`A further object is to provide such a system effective
`for illuminating a large area which may contain a vari-
`2
`
`10
`
`15
`
`30
`
`35
`
`40
`
`45
`
`50
`
`60
`
`65
`
`2
`ety of potentially explosive agents such as a hanger for
`painting commercial aircraft.
`In accordance with the present invention, the forego-
`ing objects are accomplished by providing a lighting
`system having a network ofsubstantially sealed con-
`duits through whichthe electrical wiring extends, such
`conduits being sufficiently large for a flow.of clean air
`through the network into the lamp-containing housing
`of heavy-duty fixtures. In the preferred embodiment,
`the fixture housing is substantially sealed and the clean
`air is exhausted from the housing through a manifold
`adjacent to the lens. Such clean air can be discharged
`along the face of the lens as an air curtain and/or along
`the top surface ofthe fixture housing to prevent buildup
`of potentially explosive agents and to cool the exterior
`of the housing. An automatic control system can moni-
`tor the pressure of the air in the conduit network and
`automatically cut off the supply of electric powerin the
`event of a failure.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG.1 is a top perspective of an electric lightfixture
`modified in accordance with the present invention for
`use in a lighting system for hazardous areas.
`FIG.2 is a somewhat diagrammatic rear elevation of
`the upper portionofthe lighting fixture of FIG. 1, with
`parts broken away.
`,
`FIG.3 is an enlarged section along line 3—3 of FIG.
`2 showing, in cross section, a conduit of a type usablein
`the invention, and FIG. 3A is a corresponding section
`of a modified conduit or cable.
`FIG.4 is a somewhat diagrammaticside elevation of
`the upper portion of the light fixture of FIG. 1, with
`parts broken away and parts shownin section.
`FIG.5 is an enlarged section along line 5—5 of FIG.
`
`4.
`
`FIG.6 is a schematic diagram of the gas supply sys-
`tem of a lighting system for hazardous areas in accor-
`dance with the present invention.
`DETAILED DESCRIPTION
`
`' A representative light fixture 1 of a type usable in a
`lighting system for hazardous areas in accordance with
`the present inventionis illustrated in FIG. 1. Most com-
`ponents of suchfixture 1 correspond to the “MF-HAZ”
`floodlight available from Wide-Lite of San Marcos,
`Tex. 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 substan-
`tially airtight lamp housing 2, but neither is an explo-
`sion-proof fixture approved for use in the most hazard-
`ous areas (Class 1, Division 1).
`The fixture housing 2 contains the lamp 3 and rear
`refiector 4 andhas a transparentfront lens 5. In a repre-
`sentative installation, the housing is mounted on adjust-
`able yoke arms 6 supported from a ballast casing assem-
`bly 7. Such casing assembly, in turn, is mounted on a
`long upright cylindrical mast 8 extending upward from
`a heavy base 9.
`With reference to FIG. 2, power to the fixture is
`conveyed by wires 10 extending through a sealed or
`“sealtight” conduit 11. Such wires extend into the bal-
`last casing 7 which includes among other things the
`ballast capacitor 12 accessible by a removable access
`
`Petitioner Ensign
`Exhibit 1026 - Page 6 of 9
`
`Petitioner Ensign
`Exhibit 1026 - Page 6 of 9
`
`

`

`4,937,717
`
`‘3
`plate 13. The bottom portion of casing 7 is hollow.
`Powerto 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 FIG. 3, conduit 15 is sub-
`stantially oversized as comparedto the size of the wires
`14, as is conduit 11 as comparedto the size of wires 10.
`Whenconventional electrical conduit is used, prefera-
`bly at least the major portion of the cross-sectional
`- internal area of each conduit is open and unobstructed.
`In the MF-HAZfloodlight, the line from the ballast
`casing to the lamp housingis 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 inven-
`tion, such a closed cable is replaced by the oversized
`hollow conduit 11 to allow unrestricted flow of nonex-
`plosive 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 arrowsin FIG.2.
`As best seen in FIG. 5, conduit 15 is sealed to the
`bottom lamp socket extension 16 of 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
`alongside the wires 14 to the lamp socket 17 and out-
`ward from such socket through slots 18. Gas passing
`through the slots 18 flows upward through the gener-
`ally 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 invention, one or more
`outlets 20 are provided for the gas flowing into the
`fixture. In the illustrated embodiment, two outlets 20
`extend throughthe top of the fixture housing 2 and lead
`to a long manifold 21 extending along the upperleading
`edge of the housing adjacent to the upper edge of the
`transparentlens 5, as best seen in FIG. 1 Such manifold
`has a row of closely spaced openings or holes 22 posi-
`tioned such that the gas leaves the manifold as a substan-
`tially continuous curtain blown down alongthe exterior
`of the lens 5. In addition, or alternatively, openings can
`be positioned to discharge gas rearwardalong the top of
`the housing 2 which has heat-dissipating fins 23 to assist
`in cooling the top surface of the housing Typically, the
`area immediately above and surrounding the upper
`portion of the lampis 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-
`/or along the top of the housing also helps prevent
`buildup of potentially explosive agents or agents which
`could interfere with light transmission through thelens,
`such as paint spray. Buildup on the lens can itself in-
`crease the danger by absorbing heat and increasing the
`surface temperature.
`,
`With reference to FIG.6, air to be injected through a
`plurality of the fixtures can be from the sourceof “fac-
`tory air” at a manufacturing location such as through a
`line 25. Preferably, a manually valve 26 is supplied
`allowing the supply ofair to be closed such as for main-
`tenance to the entire system. With valve 26 in its nor-
`mally open condition illustrated, the air flows to a nor-
`mally open solenoid valve 27 controlled at a central
`station such as by conventional electromechanical con-
`trols or a microprocessor 28. A pressure gauge 29 can
`be provided to monitor the pressure of air supplied
`
`.
`4
`Typically, factory air is quite dirty and may be hu-
`mid. Foruse in the presentinvention,it is important that
`the air be clean so that particulates do not collect in or
`clog any part of the system. Suchair 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 32, the supply line 25 branches to lines
`25’ each of which leads to a network offixtures 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 branch
`25’, the air supply line extends from the reduction valve
`33 to a conventional rotameter 34 to indicate the flow
`rate and, if desired, provide a signal indicative the flow
`‘rate to the microprocessor 28. Downstream of the ro-
`tameter is an additional pressure gauge 35 which,like
`gauge 29, also can supply a signal to the microproces-
`sor. In each branch 25’ leading to the individual light
`fixtures 1, an additional solenoid valve 36 is used, pref-
`erably controlled by the microprocessor 28, and an
`additional manual valve 31 is provided to be closed, for
`example, if only one branch of the lighting system re-
`quires maintenance.
`Preferably, all of the air supply components de-
`scribed above are located in the nonhazardous area NH
`which, for the purposes ofillustration,is indicated to be
`to the left of a wall W in FIG.6, as compared to the
`hazardous area H to the right of such wall. The branch
`supply lines 25’ have externally sealed joints or fittings
`37 as they extend from the nonhazardous area to the
`hazardous area.
`Within the hazardous area, preferably the air is sup-
`plied through the same network of conduits 40 and
`«junction boxes 41 used for the power supply and control
`wiring. The electrical conduits 40 have joints orfittings
`38 which are externally and internally sealed as the
`conduits enter the hazardous area and the air supply
`lines are in communication with such conduits through
`tee fittings 39. The junction boxes 41 preferably are
`substantially oversized to act as pressure accumulators.
`From each junction box, a single conduit 15 leads to the
`ballast casing for the fixture 1, and in each intercon-
`nected line of fixtures, preferably at least one junction
`box 41’ contains a pressure sensor and/or rotameter
`providing a signal to the control mechanism or micro-
`processor 28. In the event of a substantial loss of pres-
`sure or a serious overpressure condition, the supply of
`electricity to all fixtures within the same branch is auto-
`matically cut off, such as by automatically opening a
`switch 42 in the primary powersupply line. Within each
`branch individual fixtures or banks of fixtures can be
`controlled by manual switches in series with the appro-
`priate switch 42.
`Preferably, the control mechanism or microprocessor
`28 also monitors operation of the light fixtures 1 at
`start-up or restart. Prior to actuation of the lamps, air-
`flow through the fixtures should be sufficient to purge
`them of any potentially explosive agents which may
`have leaked into the fixtures. The supply ofair 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
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`35
`
`60
`
`65
`
`Petitioner Ensign
`Exhibit 1026 - Page 7 of 9
`
`Petitioner Ensign
`Exhibit 1026 - Page 7 of 9
`
`

`

`4,937,717
`
`5
`through the appropriate branch, at which timethepri-
`mary powersupply switch or switches 42 can be closed
`automatically.
`In a permanentinstallation where the positions of the
`fixtures will not change, the network of standard elec-
`trical conduits can be used. For a portable lighting
`system, however, it may be desirable to provide the
`modified conduit-cable 43 illustrated in FIG. 3A. Such
`cable has a central unobstructed hose 44 with the power
`supply and control wires 45 encapsulated in insulative
`but preferably somewhatflexible material 46 such as a
`natural or synthetic rubber which protects the wires
`and central hose from kinks and breakage, even if the
`cable is moved and flexed frequently. In mostinstaila-
`tions, 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 FIG.6, as an alternative to a sys-
`tem in which gas is continuously injected into and ex-
`hausted from each individual fixture 1, each fixture can
`be provided with a valve 47, diagrammatically indi-
`cated in broken lines in FIG. 6, controlled remotely
`such as by the microprocessor 28. At start-uporrestart,
`the primary power supply switches 42 would be opened
`and all of the valves 47 would be opened while the
`system is purged of any possible potentially explosive
`agents. After a predetermined period or amount of
`purging airflow through the system, the valves 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
`previously described embodiment, the pressure of the
`system can be monitored automatically by the control
`mechanism or microprocessor 28 to cut off the supply
`of electric power automatically if the pressure is dan-
`gerously reduced or increased above design conditions.
`Another option is to actuate valves 47 to full open
`positions for maximum flow atstart-up and restart and
`to close such valves partially after the system is purged
`to a desired degree for continuous but decreased flow of
`nonexplosive gas under normal operating conditions.
`Still another option is to increase the pressure of
`nonexplosive gas supplied to the system at 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 FIG. 6, a
`second reduction valve 33’ can be connectionin parallel
`with vaive 33 and in series with a second solenoid valve
`36’. At start-up orrestart, valve 36’ can be opened auto-
`matically to supply gas to reduction valve 23’ in addi-
`tion to the supply to valve 33. Valve 33’ can reduce the
`pressure of nonexplosive 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 automati-
`cally close solenoid valve 36’, so that during normal
`operating conditions all of the nonexplosive gas is fed
`through reduction vaive 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 lo-
`cated in the hazardous area, even close to the source of
`a potentially explosive agent. Consequently, the system
`in accordance with the present invention is adaptable
`for previously difficult illumination problems suchas to
`provide bright illumination in a paint hanger for com-
`mercial aircraft at hard to light locations such as by
`
`15
`
`25
`
`30
`
`35
`
`40
`
`45
`
`55
`
`65
`
`6
`beaming light from close to the floor underneath the
`wings and bodyofthe aircraft.
`I claim:
`1. A lighting system for an area classified as hazard-
`ous by reason of possible presence of potentially explo-
`sive agents in the ambient atmosphere, said system com-
`prising a plurality of separate lighting fixtures disposed
`in such ambient atmosphere,each ofsaid 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 sup-
`plying 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 unobstructedinterior
`passages in open communication with the interiors of
`the housings of all of said fixtures for supplying the
`clean, dry, nonambient gas under pressure into said
`fixture housings, and means for regulating the flow of
`the nonambient gas under pressure form said supplying
`means into said conduit network for controlling the
`supply of such nonambientgas to all of said housings of
`all of said fixtures.
`2. The lighting system defined in claim 1, in which
`each ofthefixture housings has an outlet for the nonam-
`bient gas, the regulating means including valves for
`closing and opening said outlets and automatic control
`means. for controlling opening and closing of said
`valves.
`3. The lighting system defined in claim 1, including
`powersupply wiring for conveying electrical powerto
`the internal lamp elements of the fixtures, said wiring
`extending along the conduits.
`4. The lighting system defined in claim 3, in which
`the regulating means includes control means for auto-
`matically monitoring the supply of nonexplosive gas
`through said conduit network, said control meansin-
`cluding meanscontrolling the supply of electric power
`to the power supply wiring.
`5. The lighting system defined in claim 3, in which a
`plurality of the fixtures include open gas outlets for
`continuous exhaust of the nonambient gas from the
`housings.
`6. The lighting system defined in claim 5, in which
`the lamp housings include transparent lenses and the
`outlets include means for discharging the nonambient
`gas from inside the housings adjacent to the exterior
`faces of said lenses.
`7. The lighting system defined in claim 6, in which
`the outlets include elongated manifolds having closely
`spaced outlet holes for discharging substantially cur-
`tains of the nonambient gas over the exteriors of the
`housing lenses.
`8. The lighting system defined in claim 3, in which
`the power supply wiring extends through the interior
`passages of the conduits.
`9. The lighting system defined in claim 8, including an
`interiorly sealed fitting at the location of introduction of
`the wiring into the conduit.
`10. The lighting system defined in claim 8, in which
`the cross-sectional size of the interior passages of the
`conduits is at least twice the aggregate cross-sectional
`size of the power supply wiring such that the portion of
`the interior passages of the conduits not obstructed by
`the power supply wiring constitutes the major portion
`of the interior passages of the conduit.
`
`Petitioner Ensign
`Exhibit 1026 - Page 8 of 9
`
`Petitioner Ensign
`Exhibit 1026 - Page 8 of 9
`
`

`

`4,937,717
`
`7
`11. A lighting system for an area classified as hazard-
`ous by reason of possible presence of potentially explo-
`sive agents, said system comprising a plurality of light-
`ing fixtures each having an electric lamp and a substan-
`tially closed lamp housing, a network of conduits hav-
`ing unobstructed interior passages in open communica-
`tion with the interior of the housings of all of said fix-
`tures, and means for injecting nonexplosive gas under
`_ pressure from outside such hazardous area into said
`conduit network for supply to all of the housingsof all
`of the fixtures, said gas-injecting means including means
`for supplying the nonexplosive gas at a first pressure for
`a desired period and, thereafter, at a second pressure
`different from the first pressure.
`12. The process of lighting an area classified as haz-
`ardous by reason of possible presence of potentially
`explosive agents in the ambient atmosphere which com-
`prises disposing in such ambient atmospherea plurality .
`of separate lighting fixtures each having an internal
`
`8
`light-producing electric lamp element and a substan-
`tially 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 underpres-
`sure which nonambient gas is devoid of the potentially
`explosive agents, such conduits having unobstructed
`interior passages in open communication with the interi-
`ors of the housings of all of the fixtures for supplying
`the clean, dry, nonambient gas under pressure into the
`fixture housings, and regulating the flow of the nonam-
`bient gas under pressure from such source into the con-
`duit network for controlling the supply of such nonam-
`bient gas to all of the housingsof all of the fixtures.
`13. The process defined in claim 12,including initially
`supplying the nonexplosive gas to thefixtures at a first
`pressure and subsequently supplying the gas to the fix-
`tures at a lower pressure.
`*
`*
`&
`&
`*
`
`10
`
`20
`
`25
`
`30
`
`35
`
`45
`
`30
`
`35
`
`65
`
`Petitioner Ensign
`Exhibit 1026 - Page 9 of 9
`
`Petitioner Ensign
`Exhibit 1026 - Page 9 of 9
`
`