US3209138A - Explosion-proof headlamp and power source - Google Patents

Description

SePt- 28, 1965 w. c. MOORE ETAL 3,209,138

EXPLOSION-PROOF HEADLAMP AND POWER SOURCE Filed Feb. 5, 1962 2 Sheets-Sheet l 2^ 48 42 E fg 45" 68 I NVENTORS WILLIAM CMOORE. AND BY WILUAM s. MLGRIM Mmmm Sept. 28, 1965 w. c. MOORE: ETAL 3,209,133

EXPLOSION-PROOF HEADLAMP AND POWER SOURCE Filed Feb. 5, 1962 2 Sheets-Sheet 2 lll /l/ l lll VIIIIII l I N VENTORS WILLIAM C. MOOREI AND 5 BYWILLIAM S. PILGRIM I; @Mww @Thx United States Patent O 3,209,138 EXPLSION-PROOF HEADLAMP AND IWER SOURCE William C. Moore, Skaneateles, and William S. Pilgrim,

Port Byron, N.Y., assiguors to Welch Allyn, Inc.,

Skaneateles Fails, NX., a corporation of New York Filed Feb. 5, 1962, Ser. No. 171,048 8 Claims. (Cl. 24U-10.6)

This invention relates to explosion-proof medical head lamps and more particularly to a headlamp having its own connected, portable, rechargeable source of electric power in which the connecting circuit is so regulated as to prevent generation of heat suliiclient to cause an explosion in case of a fault in the circuit in the presence of explosive gases usual to an operating room.

Explosion-proof lamps suitable for use in an explosive atmosphere usually depend on sealing the interior of the lamp from communication with atmosphere so that, should there be a short circuit or other fault within the lamp, no explosive gas can reach a spark or flame within the lamp. Such sealed lamps may be filled with an inert gas under pressure and may have, in connection therewith, a circuit breaking pressure sensitive switch or an incandescent bulb ejection device for cutting off the electric circuit to the bulb upon the breaking of the glass of the bulb or other damage to the lamp.

Such sealed lamps are generally too heavy to be worn on a headband if the source of electric current is self-contained, or are inconvenient and hampering if there must be a long electrical connecting cord to a remote source of power, such as a wall plug. Moreover, ordinary electrical connecting cords in themselves are dangerous in that there may be a spark or a dangerously heated area due to a short circuit or other fault in the cord sufficient to cause an explosion.

There has ,for a long time been a demand by doctors, hospitals and their insurers for a light-weight headlamp for use in the presence of explosive anaesthetic gases and adjudged safe by local regulatory rules, underwriters, and by law. The need for a source of light which may be directed by the surgeon himself on hard-to-illuminate spots is so great in some instances that frequently headlights that have not been approved by regulatory agencies are being used even though the danger is recognized.

The principal object of the present invention, accordingly, is to provide a light-weight explosion-proof headlamp adapted to be worn on a headband, the headlamp having its own connected source of electric power which is also explosion-proof and sufficiently light-weight and r portable to be carried in a pocket or pouch supported on the person or mobilely supported nearby.

Another important object is to provide a headband-supported lamp and an independently supported unitary battery power source which is freely portable and rechargeable and separably connected to the lamp so as to be easily and quickly replaceable, and which lamp, power source, and electrical connecting means are all explosion-proof.

A further object is to provide a headeborn lamp which is easily adjusted and directed, together with a portable, rechargeable dry-cell battery pack for powering the lamp, the pack and lamp each having an explosion proof housing, and separable means electrically connecting the lamp and battery pack in a low-voltage circuit so controlled as to be incapable, even when there is a fault in the circuit,

3,2938 Patented Sept. 28, 1965 to cause an explosion of any explosive gases which may ybe encountered in an operating room.

A still further object is to provide separate `but connectable lamp and battery pack units, each of which is housed so as to be explosion-proof, each of which is rugged in construction, and each having the interior thereof so closed as to suppress the propagation of llame to the outside should an explosion accidentally take place therein.

Other objects and advantages will become apparent from the lfollowing description taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a side elevational View, partly in section on the line 1 1 of FIG. 2, of a headlamp assembly according to the present invention;

FIGURE 2 is an end elevation thereof as viewed from the right of FIG. l;

FIGURE 3 is a longitudinal sectional View on the line 3 3 of FIG. 5 of the lamp assembly shown in FIG. l;

FIGURE 4 is a side elevational View of the male portion of the separable connector used with the connecting cord of the headlamp assembly of FIG. l;

FIGURE 5 is an end view of the lamp assembly of FIG. 3 as viewed from the right;

FIGURE 6 is a top plan View on a reduced scale of the battery pack used with the headlamp assembly of FIG. 1, with cover removed;

FIGURE 7 is a transverse sectional View on the line 7 7 of FIG. 6; and

FIGURE 8 is a wiring diagram of the headlamp, battery pack, and connecting circuit of the explosion proof headlamp of FIGURES l-7.

In FIGURES 1 and 2 of the drawings, a headlamp assembly 10 comprises a lamp assembly 11, a socket assembly 12, and a lens holder assembly 13.

The lamp assembly 11, best seen in FIGURES 3 and 5, is provided with an incandescent lbulb 14, including a glass envelope and an incandescent filament 16 supported within the envelope by the lead wires 17 and 18. The lead wires pass through the envelope, being sealed therein and lead wire 17 is secured by a screw 19 in electrical contact with the lamp body 2i).

The lamp body is cylindrical, hollow, and open at one end so as to be adapted to receive envelope 15 therein. The body 20 has an exteriorly threaded annular boss 21 at its closed end and the central bore 22 of the boss is threaded to secure an insulating plug 23 therein. The plug 23 is tubular and has a headed metal central contact member 24 extending therethrough, the lead wire 18 being joined lby soldering to the inner end of the contact 24. The outer end of the central contact 24 is provided with a C-washer 25 to secure the contact in the plug 23. A set screw 26 in the boss 21 locks the plug 23 in the bore 22 of the boss, and the incandescent bulb 14 is secured and supported within body 20 by cementitious supporting material 27 packed into the closed end of the body.

The open end of the body Z0 is reduced in diameter to provide a shoulder at 28 and is exteriorly threaded. An interiorly threaded cap member 30 is screwed to the body 20 against the shoulder 2S and is locked in place by a set screw 29. The outer end of the cap member 30 is provided with an annular shoulder 31 about an orifice 32 and an annular lock nut 33 with a similar orifice secures a glass window or plano-plano lens 34 in position against the shoulder 31. The window 34 is sealed between nut 33 and shoulder 31 as indicated at 35 as by means of an epoxy cement capable of adhering to both glass and metal over a suitable range of temperatures. Body 20, cap 30 and nut 33 are preferably of aluminum for strength and lightness and the supporting material at 27, which is heat resistant, non-corrosive and a non-conductor, adheres to this metal and to the glass of envelope and hardens quickly without appreciable shrinking. The material 27 thus supports the envelope within the central closed chamber 36 of the lamp body, there being clearance as indicated at 37 between envelope 15 and window 34 to allow for expansion of the envelope when heated.

The socket or receptacle assembly 12 is best seen in FIGURE 1 and includes a hollow receptacle body 40, also preferably of aluminum, having a cylindrical sidewall 41 and one end wall 42. Side wall 41 has an interior diameter substantially equal to the outside diameter of the lamp body 11. The end wall has a ball post 43 secured thereto for adjustably supporting the headlamp assembly on the headband in conventional manner, and is provided in the interior of the body with an insulating disk 44.

Telescoped within sidewall 41, an annular socket member 45 is locked in place by a set screw 46 to divide the interior of the receptacle body 40 into the terminal chamber 47 and the socket chamber 48. Socket member 45 has an interiorly threaded annular sidewall portion 49 projecting toward the open end of body 40 into which the boss 21 of lamp assembly 11 is screwed. The socket member is also formed with a rearwardly projecting, centrally bored, end-wall boss 50 in the terminal chamber 47.

A two-piece, centrally bored, terminal Contact plug 51- 52 is secured in the central bore of the socket member boss 50. The outer insulating member 51 of the plug has a shouldered head countersunk in the end wall of the socket member 45, and its other end has an enlarged bore in which the inner member 52 of the plug is wedged to secure the plug in the central bore of the boss 50. A spring contact 53, in electrical contact with the central contact 24 of lamp 11, is secured to one end of the plug 51-52, by an electrical conductor screw 54 having a nut 55 at the other end of the plug in chamber 47, the screw 54 passing through the central bores of the plug pieces 51 and 52.

The sidewall 41 of chamber 47 has a passage 56 (FIG. 2) therethrough and in this passage is engaged a strain relieving nylon plug 57. One end of an electrical connecting cord 58 is passed through the plug 57 and the lead wires 59 and 60 of the cord 58 extend into the terminal chamber 47. A terminal at the end of wire 59 is secured by the nut 55 in electrical contact with the conductor screw 54, and the end of wire 60 is secured in electrical contact with boss 50 by the screw 61:,-

The lens holder assembly 13 comprises a sleeve member 65, a lens holder or end piece 66 and a plano-convex lens 67. The sleeve member 65 is tubular and adapted to iit telescopically and slidably about the lamp body and cap member 30 to permit relative longitudinal movement for focusing. The outer end of sleeve member 65 is internally threaded to receive an externally threaded portion of the end piece 66.

End piece 66 is annular, having a shouldered orifice 68 axially aligned with window 34 and lament 16. Lens 67 is secured cementitiously against the shoulder of the orifice 68 and a blue filter 69 may be cemented in place adjacent the inner iat surface of the lens. The outer cylindrical sidewalls of sleeve 65, receptacle member 40, lamp body 20 and cap member 30 are grooved as shown and the parts are oxidized or anodized black throughout to aid in the absorption and dissipation of heat,

The connecting cord 58 is lprovided with a jack-type separable connector, the male portion 70 of which is shown in FIG. 4. The wires 59 and 60 of connecting cord 58 are connected respectively to the contacts 71 and 72 at the end of jack post 73, the contacts being insulated one from the other in the usual manner.

The female portion 75 of the separable connector is shown in FIGURE 7 connected in similar manner to another portion of the connecting cord 58. It is understood that the portion 75 has a cylindrical recess 76 mating with the jack post 73 with suitable insulated mating contacts at the bottom thereof.

Referring more particularly to FIGURES 6 and 7, the battery pack assembly is connected by the cord 58 to the headlamp assembly 10.

As best seen in FIGURE 7, the battery pack comprises a housing, also of aluminum, having a receptacle portion or body 81 and a top 82, the two parts being threadedly joined at 83 and locked in place by the set screw 84 to enclose a central chamber 85. It should be noted that this threaded junction of the two closure parts has at least five threads in engagement when the two parts are assembled. The same live-threaded engagement of closure parts is maintained in all the threaded junctions in the headlamp assembly 10 as well as in connection with the set screw locking means provided with each.

The exterior of body 81 and top 82 are provided respectively with shock resisting, electrically conducting neoprene rubber covers 86 and 87 cemented to their respective parts by an adhesive resistant to the liquids and gases ordinarily encountered in hospitals.

In chamber a cup-shaped power cord housing 88 of aluminum is threadedly engaged at 89 with a suitable hole through the bottom of body 81. The bottom of the housing 88 has an entrance passage 90 therethrough in which is lodged a strain-relieving nylon plug 91 at the end of the connecting cord 58.

The wires 59 and 60 of the cord extend through the interior chamber 92 of housing 88 and through an insulating bushing 93 in an annular nut 94 threadedly engaged with the top end of the housing 88. Chamber 92 is closely packed with a tire-resistant, discrete, fibrous, packing material, preferably asbestos rope.

At the center of chamber 85 a cup-shaped aluminum resistor housing 95 is located in contact with the bottom wall or iioor 96 of the receptacle or body 81, and an axially disposed center post 97 of aluminum is threadedly secured to the bottom of housing 95. The center post 97 supports a current liming resistor 98 in the interior chamber 99 of the housing 95 and a key 100, in appropriate slots in housing 95, post 97 and resistor 98, prevents the resistor from turning with respect to the housing. A nylon insulating sleeve 101 surrounds the resistor housing and a Teflon cover plate 102 covers the housing inside the sleeve. Appropriate registering holes are provided in sleeve 101 and housing 95 for the hereinafter described connecting wires to the resistor 98,

Disposed around the resistor housing 95 on either side of the power cord housing 88 are five rechargeable drycell batteries 103, preferably of the nickel-cadmium type. The batteries are connected in series by connecting wires 104 as shown, it being understood that alternate batteries are inverted so that each battery is connected at the top to the battery on one side and at the bottom to the battery on the other side. Annular grooves 105 and 106 are provided in the bottom Wall 96 of the body and the underside of top 82 to provide space for the connecting wires 104. The connecting cord lead wire 59 and resistor 98 are also connected in the series circuit with batteries 103, wire 59 being connected to the resistor and wire 60 being connected to one of the batteries, as shown.

Insulating strips 107 of paper or other suitable material are provided, as best shown in FIG. 6, to separate adjacent batteries and a sleeve 108 of similar material is provided for housing 88. Shock-absorbing disks 109 and 110 of sponge rubber are provided between the batteries and v the bottom 96, and a similar hole is provided for housing 88.

It will be noted that the batteries 103 are rmly held in place by the sponge rubber padding 109, 110, 111, and the batteries and housings 88 and 95 are compactly arranged in chamber 85 so as to leave a minimum of empty space within the pack 80. The batteries shown each have a rated Voltage of less than a v-olt and a half. Resistor 98 has a similar low rating of 1.3 ohms for a 5 watt light source and limits the current available in the low voltage connecting circuit shown in FIGURE 8 in case of a short circuit or other fault.

It will also be understood that larger batteries may be similarly used in an enlarged or heavier pack to give longer life between rechargings, but the same low voltage and restriction in the current available may be maintained. `Such larger packs are more conveniently supported behind the user on a mobile stand, such as an infusion stand which is readily available in hospitals. The smaller and lighter pack 80, however, is adapted to be carried in a pocket, or in a pouch strapped around the waist of the user.

In operation the pack is carried in any convenient manner and the headlamp assembly :10 is worn on a headband. To turn the lamp on, the parts 70 and 7S of the separable connector are joined. Current Hows from the batteries 103 through resistor 98 and the connecting circuit to the incandescent bulb 14. Light from the lilament -16 may be concentrated at any desired distance from the headlamp by moving the lens holder assembly telescopically to carry lens 67 away from or toward the window 34 in the usual manner.

The headlamp 10 is of very rugged construction and has la minimum of unoccupied space therein. The incandescent :bulb 14 is firmly supported in the chamber 36, but should the glass envelope 15 :be shattered, for any reason, the still glowing iilament 16 is completely enclosed in the chamber 36.

No attempt has been made to pressurize this chamber or to seal it or chambers 47 and 48 with high pressure seals to make them vapor proof. The threaded connections between the component parts of the headlamp and pack assemblies may be pervious to explosive gases, as are the power cord entrances to the receptacle 12 and pack housing 81-82 which are respectively engaged by the nylon plugs 57 and 91.

Chamber 36, however, is provided at one end with the comparatively thick glass window 34 sealed at 35 to the cap 30. Moreover, chamber 36 is surrounded, at this end, by the sleeve 65 and associated parts.

At the other end of chamber 36 the socket chamber 4S enclosing contacts 53 and 24 communicates with the lirst chamber 36 only along the tightly tting insulating plug 22 and the inner end of the plug is sealed by the covering of cementitious supporting material 27. The chamber 47, in which the terminal ends of wires 59 and 6@ are contained, is not sealed but its entrance passage supports the strain relieving plug 57.

Should explosive gases seep into the comparatively small unoccupied space in chamber 36 and an explosion occur therein, the walls of the chamber are amply strong to contain the explosion as has been demonstrated by test. The devious and tortuous minute passages along the threaded connections or between the tightly fitting parts between the chamber 36 and the exterior of the headlamp assembly suppress any propagation of liame outside the headlamp.

The interior chamber 85 of the battery pack 80 is also screened from direct communication with an explosive atmosphere outside the pack. Communication from chamber -85 to the exterior of the pack housing is only along the threads at 33, or along the threaded junction 89 between the cord housing 88 and the bottom wall 96, or through housing 88 and past the plug 91 in passage 91B. This last mentioned path, of course, is through the tightly packed asbestos rope at 92. Any of the paths of communication between the chamber and the outside of the pack is thus along a tortuous and devious route between closely fitting particles or walls which suppress the propagation of tflame from within the battery pack.

The low voltage connecting circuit between batteries 103 and lament 16 has the current limiting resistor 98 wires in series therein. Should the cord 58 become worn or short circuited the current is limited by the resistor, preventing even an instantaneous surge, and the heat which can be produced by a fault in the cord 58 is limited to an amount well under that required to ignite the anaesthetic gases ordinarily encountered.

Both `battery pack and headlamp assembly are sufiiciently rugged in construction to meet the strictest underwriters tests for accidental breakage and are designed for rapid heat dissipation. The black coloration and grooved outer surfaces of the headlamp assembly collect and dissipate the heat so that the exterior surface may be comfortably handled even after extended use. In the pack 80, the housing in its nylon sleeve acts as a heat sink for the resistor 98. Should the resistor become overheated because of a short circuit, the post 97 carries the heat freely to the bottom of housing 95 and thence to the bottom 96 of the pack housing to dissipate the heat throughout the entire housing.

It will be apparent that by providing the separable connector 70, 7S between pack and lamp, the need for a switch is eliminated and also means are provided for removing a pack which has become exhausted through use and substituting another fully charged pack. The pack which has been removed may then be recharged by plugging its connector 75 into a battery charger provided with a connector pack-post similar to that shown at 73, FIGURE 4.

[As will be apparent to those familiar with the art, the invention can :be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The embodiment disclosed is therefore to be considered in all respects as illustrative rather than restrictive, the scope of the invention being indicated by the appended claims.

What is claimed is:

1. An explosion-proof headlamp having its own connected source of electricity and adapted to be worn in an explosive gas atmosphere, comprising: a light-weight lamp assembly having a rst closed chamber and a second chamber having threadedly interengaged walls, said rst chamber having a sealed transparent window in one wall thereof, a sealed glass lamp envelope supported in the iirst chamber and having a filament and exterior lead wires connected to the filament, a pair of terminals supported in the second chamber, current carrying means connecting the terminals to the lead wires with at least one such means being insulated in the wall bet-Ween said chambers; a battery pack assembly having threadedly engaged housing parts deiining a central closed chamber, a plurality of low-voltage rechargeable dry type battery cells and a discharge current limiting resistor mounted in said central chamber; and insulated current conducting means including a ilexi'ble cord connecting said terminals and said batteries and resistor in a low-voltage series circuit, said second chamber and said central chamber having entrance passages for said cord, a resilient strainrelieving plug around the cord at each of said entrance passages, and discrete non-inflammable iibrous packing material around the cord in said central chamber entrance passage, whereby current is limited in said cord lfor preventing overheating in case of a fault in the cord, and said first chamber is closed to suppress the propagation of any flame therein to the outside.

2. An explosion-proof head1-amp adapted for use in an explosive gas `atmosphere comprising: a tubular closed walled chamber having a sealed transparent window forming one end wall thereof; a sealed glass envelope in said chamber; an incandescent ilament in said envelope; lead wires extending from said iilament through said glass envelope; a tirst insulated contact in the other end wall of said chamber and connected to one of the lead wires; cementitious material supporting said glass envelope in the chamber; a second walled chamber having therein a second insulated contact in resilient connection with said rst contact; a third walled chamber having therein a rst terminal secured in electrical contact with said second insulated contact and a second terminal electrically connected to the other iilament lead wire, one wall of said third chamber having an entrance passage therethrough; a resilient plug engaged in said passage, and a pair of insulated wires each connected to a respective one of said terminals passing through said plug for connecting said lilament with a source of electric current.

3. The headlamp of clai-m 2 having a tubular sleeve telescopically engaged about one end thereof, said sleeve having a shouldered orifice at one end aligned with said transparent window and lament, and a plano-convex lens secured in said orice against the shoulder for focusing light from the iilament by moving said sleeve telescopically.

4. An explosion-proof medical headlamp adapted to be worn on a headband, comprising: a hollow supporting base portion having a cylindrical sidewall and one wall adapted to be secured to the headband; said sidewall having a passagetherethrough; a resilient plug engaged in said passage; an electrical connecting cord adapted to be connected to a source of electric current and having one secured in said plug; an annular metal socket member telescopically fitted and secured within said base portion and dividing the interior thereof into a terminal chamber and a socket chamber; said cord having wires extending into said terminal chamber; an axially extending bore through said socket member; an axially bored insulator plug in said socket member bore; a spring contact at one end of said insulator plug; electrically con- V/ductive means through said plug bore securing said spring contact to one end of the plug and one of said Wires to the other end of the plug; the other wire being secured in electrical contact with the socket member; said socket member having an annular internally threaded sidewall extending axially away from said spring contact member; a cylindrical metal lamp body having an annular boss at one end threadedly engaged within said internally threaded sidewall; said lamp boss having a threaded central bore therein; a tubular insulator threadedly engaged in said central bore; a metal center contact secured Within said tubular insulator and having one end in contact with said spring contact; a lamp including a glass envelope, a filament sealed in the envelope, and lead wires extending from the li'lament outside the envelope; one lead wire being secured in electrical contact with said lamp body and the other lead wire being secured in electrical Contact with said center contact; cementitious supporting material securing said lamp envelope Within said lamp body; a cylindrical hollow lamp top cap threadedly engaged at one end with said lamp body and having a shouldered oriice at the other end, set screw means locking said top cap and lamp body in engagement, an annular nut threadedly engaged within said top cap, and a glass window secured between said shouldered oriiice and said annular nut and cementitiously sealed therebetween, whereby said lamp is enclosed for preventing the propagation of a llame outside of said headlamp.

5. An explosion-proof battery pack adapted to be carried in a pouch and connected for use with a medical headlamp in an explosive gas atmosphere, comprising: la metal housing having two threadedly engaged portions defining a central closed chamber, a plurality of rechargeable sealed, dry type battery cells and discharge current limiting means positioned in said chamber, an entrance passage tothe chamber in saidv housing,- a connecting oord adapted to be connected to the headlamp andphaving a resilient plug at one end engaged in said passage, said cord having wires extending into said chamber and connecting said battery cells and current limiting means in series, and discrete non-iniiammable iibrous material packed in said passage about said Wires whereby the propagation of any flame in the chamber to the outside is suppressed.

6. An explosion-proof battery pack adapted for use with a medical headlamp in an explosive atmosphere, comprising: a hollow metal body having a receptacle portion and a cover portion threadedly interengaged to provide a closed body chamber; means for locking said receptacle and cover portions in engagement; a plurality of dry rechargeable batteries and a discharge current-limiting resistor disposed within said body chamber and connected in series; an entrance chamber within said body chamber having a passage at one end leading outside said body and communicating at its other end with said body chamber; a connecting cord having one end adapted to be connected to the headlamp and having electrically conductive wires at its other end leading through said passage and said entrance chamber and being connected in said body chamber to said batteries and resistor; and discrete noninflammable liibrous packing material in said entrance chamber tightly packed about said wires; whereby communication from the interior of said body chamber to the atmosphere is so minutely tortuous and devious as to suppress propagation of liame from said body chamber to the explosive atmosphere.

'7. The battery pack of claim 6 having conductive, resilient, shock-absorbent covering material adhesively secured to the outer surfaces of said metal body, and having a lining of soft and resilient insulating material disposed between the walls of said body chamber and said batteries, whereby injury to said body and its contents is prevented if the pack is accidentally dropped.

8. An explosion-proof battery pack adapted to be carried in a pouch and connected for use with a medical headlamp in an explosive atmosphere, comprising: a hollow metal body having a receptacle portion and a cover portion threadedly interengaged to provide a cylindrical closed chamber; set screw means for llocking said receptacle and cover portions in threaded engagement; a layer of electrically conductive, resilient, shock-absorbent material adhesively secured to the outer surfaces of said body; a layer of soft resilient electrical insulating material disposed about the walls of said closed chamber, a cylindrical hollow power cord housing in said chamber threadedly secured at its outer end to said body; an entrance passage through said body into said cord housing; a resilient plug in said passage; a power cord having one end passing through the plug and being adapted at the other end for connection to said headlamp, said cord having electrically conductive wires extending into said chamber through said housing; asbestos rope in said housing packed about said wires; a hollow cylindrical resistor housing in contact with said body and centrally disposed in said chamber; a discharge current limiting resistor secured within said resistor housing; an insulating sleeve about said resistor, said sleeve having a cover therefor; and a plurality of rechargeable cylindrical battery cells disposed in said chamber about said resistor housing on either side of said power cord housing so as to substantially fill said chamber; said cells and said resistor being connected in a series circuit with said power cord wires for illuminating said headlamp, said resistor housing and sleeve having passages therethrough for said connection, whereby current through said cord is limited to generate less heat than needed to ignite the explosive atmosphere in case of a fault in the cord, and said entrance passage for the cord is so tortuous and devious by reason of said asbestos packing as to suppress propagation of a llame from Within said chamber to the explosive atmosphere.

References Cited by the Examiner UNITED STATES PATENTS Wappler 240-1066 Yost 240-112 Wheat 240-106 Watkins 240-10.6 10 Blood 240-11.2

Merrill 24U-10.6 Arnesen 128-23 Gellman 12S-22 McNail 240-10.6 Muller 240-10.61 Werner 24U-10.6 Font 174-52 Amlee 240-52 Monroe 24U-123 X NORTON ANSHER, Primary Examiner.

Claims (1)

1. AN EXPLOSION-PROOF HEADLAMP HAVING ITS OWN CONNECTED SOURCE OF ELECTRICITY AND ADAPTED TO BE WORN IN AN EXPLOSIVE GAS ATMOSPHERE, COMPORISING: A LIGHT-WEIGHT LAMP ASSEMBLY HAVING A FIRST CLOSED CHAMBER AND A SECOND CHAMBER HAVING A SEALED TRANSPARENT WINDOW IN ONE FIRST CHAMBER HAVING A SEALED TRANSPARENT WINDOW IN ONE WALL THEREOF, A SEALED GLASS LAMP ENVELOPE SUPPORTED IN THE FIRST CHAMBER AND HAVING A FILAMENT AND EXTERIOR LEAD WIRES CONNECTED TO THE FILAMENT, A PAIR OF TERMINALS SUPPORTED IN THE SECOND CHAMBER, CURRENT CARRYING MEANS CONNECTING THE TERMINALS TO THE LEAD WIRES WITH AT LEAST ONE SUCH MEANS BEING INSULATED IN THE WALL BETWEEN SAID CHAMBER; A BATTERY PACK ASSEMBLY HAVING THREADEDLY ENGAGED HOUSING PARTS DEFINING A CENTRAL CLOSED CHAMBER, A PLURALITY OF LOW-VOLTAGE RECHARGEABLE DRY TYPE BATTERY CELLS AND A DISCHARGE CURRENT LIMITING RESISTOR MOUNTED IN SAID CENTRAL CHAMBER; AND INSULATED CURRENT CONDUCTING MEANS INCLUDING A FLEXIBLE CORD CONNECTING SAID TERMINALS AND SAID BATTERIES AND RESISTOR IN A LOW-VOLTAGE SERIES CIRCUIT, SAID SECOND CHAMBER AND SAID CENTRAL CHAMBER HAVING ENTRANCE PASSAGES FOR SAID CORE, A RESILIENT STRAINRELIEIVING PLUG AROUND THE CORE AT EACH OF SAID ENTRANCE PASSAGES, AND DISCRETE NON-INFLAMMABLE FIBROUS PACKING MATERIAL AROUND THE CORD IN SAID CENTRAL CHAMBER ENTRANCE PASSAGE, WHEREBY CURRENT IS LIMITED IN SAID CORD FOR PREVENTING OVERHEATING IN CASE OF A FAULT IN THE CORD, AND SAID FIRST CHAMBER IS CLOSED TO SUPPRESS STHE PROPAGATION OF ANY FLAME THEREIN TO THE OUTSIDE.

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