EXPLOSION-PROOF LIGHTING DEVICE

Abstract: An explosion proof lighting device which is suitable for lighting an area which is at risk of explosion, belonging to zone zero, comprising a housing (1), a light source (3) which is situated in the housing, a light guide (4), one end of which is connected to the housing, a light head (5), which is arranged at the other end of the light guide, and a power supply (6) to the housing in order to provide at least the light source with energy. The housing is provided with an air feed line (7) for feeding air, while the device is operating, to the housing from an air source which is at a distance from the housing, in order to maintain an excess pressure in the housing with respect to the environment. The housing is also provided with a pressure-monitoring system, which ensures that the device is switched off safely if the excess pressure in the housing becomes too low or too high.

Description: Explosion-proof lighting device The present invention relates to an explosion-proof lighting device which is suitable for lighting an area which is at risk of explosion, belonging to zone zero, comprising a housing, a light source which is situated in the housing, a light guide, one end of which is connected to the housing, a light head, which is arranged at the other end of the light guide, and a power supply to the housing in order to provide at least the light source with energy. Areas which are at risk of explosion are divided into different zones. Zone zero is the zone which is most at risk. The next zone is zone one. According to safety regulations, the heat emitted by a lamp means that a light source of a lighting device must never be positioned in zone zero. The light source may be positioned in zone one, provided that the housing is of -explosion-proof design. The light has to* e carried in cold form to zone zero via a guide. An example of a zone zero area is an aircraft wing, since this is where the fuel tanks of the aircraft are accommodated. When inspection work is carried out in the wing, the technicians have to crawl into the wing. They are never allowed, for example, to take a torch with them. It is therefore necessary to position a light source at a distance from the aircraft wing and for the technicians to carry with them a light guide in order to be able to illuminate the wing on the inside. Light is always lost in a light guide, as a function of the material used and the length of the guide. It is therefore desirable for the light source to be arranged as close as possible to the areas which are to be illuminated, in order for the length of the light guide to be kept as short as possible and, as a result, to restrict the loss of light in the light guide. An explosion-proof lighting device of the type described in the preamble is known from EP-A-0 533 987. When this known device is used, the light head and a part of the light guide which is connected thereto are brought into the zone zero area. The housing and the other part of the light guide which is connected thereto is arranged outside the zone zero area. To be able to comply with the explosion-proof requirements, the housing is of heavy design. This constitutes a drawback. It is an object of the present invention to provide a device for lighting a zone zero area in which the housing together with a light source with a relatively high light output may be positioned in zone one without the housing having to be of heavy design. This object is achieved by a lighting device of the type described in the preamble in which the housing is provided with an air feed line for feeding air, while the device is operating, to the housing from an air source which is at a distance from the housing, in order to maintain an excess pressure in the housing with respect to the environment. As a result of light being supplied from outside the zones which are at risk of explosion and an excess pressure being maintained in the housing with respect to the environment, there is no risk of explosion inside the housing. In the event, for example, of seals failing, there is no risk of explosive gases or vapours entering via the light guide or via leadthroughs in the housing. Preferred embodiments of the lighting device according to the invention are defined in the subclaims . In the description which follows, the invention will be explained with reference to the drawing, in which the only figure diagrammatically depicts a specific embodiment of the lighting device according to the invention. In the figure, zone zero and zone one of an area which is at risk of explosion are shown as separated from one another by a dashed line. A housing 1, in which a light projector 2 is arranged, is located in zone one. The housing 1 is preferably made from metal, in particular stainless steel. The light source 3 is situated in the projector 2. A light guide 4 is fitted in order to carry the light from the light source 3 to zone zero. One end of the light guide 4 is arranged in the vicinity of the light source 3. At the other end of the light guide 4, there is a light head 5, by means of which the light can be focussed in zone zero and can be directed in a defined direction. The light guide 4 is preferably a synthetic fibre-optic cable, but may also be a glass fibre-optic cable. The light guide 4 is preferably surrounded by a wound or braided metal sheath. The metal used is preferably stainless steel, but may also, for example, be copper. The metal sheath is earthed, so that electrostatic charging of the light guide 4 is counteracted and any sparking is prevented. The metal sheath is also used to protect the light guide 4 from damage. The light guide 4 with its sheath may be flexible, such as a hose, so that the light guide 4 can even be used in a tight, complex space, such as for example an aircraft wing. Another advantage is that a wound or braided sheath may be light-permeable, with the result that a person who is in a tight, complex space with the light guide can find his way back using the light guide, which emits light over its entire length. The housing 1 is provided with a power supply line 6 for supplying energy for, inter alia, the light source 3, to the housing 1 from outside the area which is at risk of explosion. The housing 1 is also provided with an air feed line 7 and an air outlet 8 with a restricted passage. Air is carried out of an area which lies outside the area which is at risk of explosion to the housing 1 via the air feed line 7, in order, by interacting with the air outlet 8, to keep the housing 1 at an excess pressure with respect to the environment. This air may be derived from a compressor or from a compressed-air system. The light projector 2 is provided with a fan 9, in order, inter alia, to cool the light source 3. The housing 1 is also provided with a pressure-monitoring system. This system comprises pressure sensors (not shown) for measuring the pressure in the housing 1. The pressure-monitoring system also comprises a control unit 10 and a container 11 in which there is an emergency supply of compressed air. From the container 10, an air line 12 leads to the inside of the housing 1. The air line 12 has a mouthpiece 13 which is directed onto the light source. Valves 14 and 15 are fitted in the lines 7 and 12, respectively, which valves can adopt a position between a closed position and an open position. These valves 14 and 15 are preferably solenoid valves. A valve 16 is also fitted in the air outlet 8. In the power supply 6 there is a switch 17. This switch 17 can be used to interrupt the supply of energy to the light source 3. The control unit 10 is electronically connected to the valves 14, 15 and 16 and to the switch 17. The pressure sensors are also electronically connected to the control unit 10. * During normal operation, the control unit 10 uses the valves 14 and 16 to control the flow of air and therefore the excess pressure in the housing 1. If, in the housing 1, the excess pressure disappears completely or partially with respect to the environment, with the pressure sensors measuring a significant drop in the pressure, the control unit 10 sends a control signal to the switch 17, with the result that the latter opens and the light source 3 is switched off. A control signal is also sent to the valve 15, with the result that air is passed from the container 11, via the line 12, into the housing 1, so that the light source 3 is cooled directly and the excess pressure in the housing 1 is maintained as much as possible until the light source 3 has reached a sufficiently low temperature. The disappearance of the excess pressure may be the result, for example, of a major air leak arising in the housing 1 or the failure of the regular air supply. The light source 3 is also switched off in the event of an excessively high excess pressure in the housing 1. When the device is started up, first of all air is circulated through the housing 1, in order to remove any hazardous gases which may be present in the housing 1, and an excess pressure is built up in the housing 1. Only then is the light source 3 ignited. The starting operation is also controlled by the control unit 10. It will be clear that other embodiments of the lighting device are also possible. For example, it is possible for the device to be designed with a plurality of light guides. In Figure 1, the light head is illustrated as a type of spotlight, but it may also be of some other form, for example in striplight form. In the lighting device according to the invention, the housing 1 with the light source 3 can be positioned in a zone one area, with the result that a zone zero area can be illuminated with a limited length of light guide 4.

Claims: CLAIMS 1. Explosion-proof lighting device which is suitable for lighting an area which is at risk of explosion, belonging to zone zero, comprising a housing, a light source which is situated in the housing, a light guide, one end of which is connected to the housing, a light head, which is arranged at the other end of the light guide, and a power supply to the housing in order to provide at least the light source with energy, characterized in that the housing is provided with an air feed line for feeding air, while the device is operating, to the housing from an air source which is at a distance from the housing, in order to maintain an excess pressure in the housing with respect to the environment. 2. Device according to claim 1, in which the housing is provided with a pressure-monitoring system. 3. Device according to claim 2, in which the pressure- monitoring system comprises means for measuring the pressure in the housing, as well as at least one compressed-air container with an emergency supply of compressed air, as well as a control unit. 4. Device according to claim 2 or 3, in which the pressure- monitoring system is designed in such a manner that, in the event of a pressure drop in the housing, the light source is switched off. 5. Device according to claim 3 or 4, in which the pressure- monitoring system is designed in such a manner that, in the event of a pressure drop in the housing, compressed air flows out of the compressed-air container into the housing. 6. Device according to one of claims 3-5, in which the compressed-air container is provided with a line for air flowing out, which is directed at the light source. 7. Device according to one of the preceding claims, in which the light guide is flexible. 8. Device according to one of the preceding claims, in which the light guide comprises bundled synthetic fibres . 9. Device according to claim 7 or 8, in which the light guide is surrounded by a wound metal sheath. 10. Device according to claim 9, in which the metal sheath of the light guide is light-permeable. 11. Device according to one of the preceding claims, in which the device is connected to a compressed-air system in order to maintain the excess pressure in the housing. 12. Device according to one of the preceding claims, in which the device is connected to a compressor in order to maintain the excess pressure in the housing. 13. Method for inspecting an area which is at risk of explosion belonging to zone zero, making use of a device according to one of the preceding claims, in which the light guide with the light head is used in zone zero and the housing is positioned outside this zone.

Inventors: KEIJZER EDWIN, KEIJZER, EDWIN
Applicants: IBG FIBER OPTICS B V, KEIJZER EDWIN, IBG FIBER OPTICS B.V., KEIJZER, EDWIN
Application year: 2001
Main classification: F21V25
IPC codes: F21V25