GB2217200A

GB2217200A - Explosion protection system

Info

Publication number: GB2217200A
Application number: GB8808202A
Authority: GB
Inventors: Geoffrey R Oliver
Original assignee: Pyroban Ltd
Current assignee: Pyroban Ltd
Priority date: 1988-04-08
Filing date: 1988-04-08
Publication date: 1989-10-25
Also published as: GB8808202D0

Abstract

An explosion protection system comprises an inner enclosure (20) which shields a potential source of ignition (E), a first sensor (S1) arranged to actuate a purge over the enclosure (20) on detection of a hazardous atmosphere outside the enclosure (20), and a second sensor (S2) arranged to render safe the potential source of ignition (E) on detection of hazardous atmosphere within the inner enclosure (20). The inner enclosure (20) may be pressurised so as to resist ingress of gases. There may also be an outer enclosure (30) which may for example be the room in which the potential source of ignition (E) is situated. <IMAGE>

Description

PROTECTION SYSTEM The present invention relates to protection systems, for example to systems designed to reduce the risk of explosions when electrical apparatus is used in potentially explosive atmospheres.

One known method of protection against ignition by electrical apparatus operating in potentially hazardous atmospheres is known as the EXP system. This uses a continuously-running air purge to reduce the concentration of potentially explosive gases surrounding the electrical apparatus to a value at which ignition will not occur. The disadvantage of this is that large amounts of air are required, so necessitating the use of large high-pressure gas cylinders, which need to be regularly replaced.

An alternative protection has more recently become available in which the atmosphere surrounding the apparatus is not controlled. Instead, a suitable detector is provided near the equipment which monitors the-level of explosive gases in the ambient atmosphere, and shuts the equipment down should this level become dangerously high. The problem with this is that many users of electrical equipment do not like having to shut the equipment down every time the ambient atmosphere becomes hazardous, particularly if this occurs frequently but only for a relatively short period each time.

It is an object of the present invention at least to alleviate the problems of the prior art.

It is a further object to provide a protection system which is safer than the EXP system, while at the same time allowing , the equipment to be protected to continue running in normal circumstances even if the ambient atmosphere becomes hazardous for a short period.

According to the present invention an explosion protection system comprises an inner enclosure arranged in use to shield a potential source of ignition, a first sensor arranged to actuate a purge over the enclosure on detection of a hazardous atmosphere outside the enclosure, and a second sensor arranged to render safe the potential source of ignition on detection of a hazardous atmosphere within the inner enclosure.

The enclosure can, if desired, be pressurised so as to resist ingress of gases; but this is not essential.

The purge is desirably an air purge, and is conveniently achieved by means of a conventional air line.

Where the potential source of ignition arises from the operation of an electrical apparatus, it may be rendered safe by switching it off. Alternatively, where the potential source of ignition is a flame or other source of heat, then it may be rendered safe by extinguishing it. It would also be possible (although it is probably not desirable from a commercial point of view) for the potential source of ignition to be rendered safe by applying a high-pressure purge to the interior of the inner enclosure.

The second sensor may be positioned within an outer enclosure, which itself shields the inner enclosure. With such an arrangement, the interior of the outer enclosure is purged when the second sensor detects a hazardous atmosphere.

The second sensor may be sensitive to the level of one or more explosive gases; or alternatively sensitive to some other hazard such as the amount of explosive dust present.

The invention may be carried into practice in a number of ways and one specific exemplary protection system, illustrated in Figure 1, and its method of operation, will now be described by way of example.

Figure 1 shows an embodiment of the protection system being used to protect an item of electrical equipment 10. The equipment is surrounded by an enclosure 20 so as at least partially to shield it from the ambient atmosphere. If desired, the shielding provided by this enclosure could be increased either by providing for an over-pressure within the enclosure, or by arranging for a continuous flow of non-hazardous air to pass through it.

Surrounding the enclosure 20 is an external enclosure 30. This could be an especially built enclosure or could, for example, comprise the room in which the equipment is situated. In some circumstances, it could even be dispensed with altogether.

Hazard detectors S1 and S2 are provided respectively within the enclosure 20 and within the external enclosure 30. The purpose of these detectors is to determine when the level of explosive gases in the atmosphere reaches a dangerous value, or more generally to detect when the atmosphere becomes hazardous.

On sensing a hazardous atmosphere within the external enclosure 30, the detector S1 switches on a purging system P; this continues to operate until the atmosphere within the external enclosure 30 becomes safe again. It will be appreciated, of course, that since purging is only carried out when a hazardous atmosphere is detected, in contrast to the present EXP system in which purging is carried out continuously, far less air is required. This means that a conventional air line can be used, in contrast to the expensive high-pressure cylinders presently required.

If the detector S2 detects a hazardous atmosphere within the internal enclosure 20, then the equipment is shut down. Thus, in the event that such a high concentration of explosive gases is present that the purging system is unable to cope, the system will still protect against the risk of explosion.

Claims

1. An explosion protection system comprising an inner enclosure arranged in use to shield a potential source of ignition, a first sensor arranged to actuate a purge over the enclosure on detection of a hazardous atmosphere outside the enclosure, and a second sensor arranged to render safe the potential source of ignition on detection of a hazardous atmosphere within the inner enclosure.

2. An explosion protection system as claimed in Claim 1 in which the enclosure is pressurised so as to resist ingress of gases.

3. An explosion protection system as claimed in Claim 1 or Claim 2 including an air line for effecting an air purge on detection of a hazardous atmosphere outside the inner enclosure.

4. An explosion protection system as claimed in any one of the preceding claims including means for rendering safe electrical apparatus within the inner enclosure by switching it off.

5. An explosion protection system as claimed in any one of the preceding claims including means for rendering. safe a flame or source of heat within the inner enclosure by extinguishing it.

6. An explosion protection system as claimed in any one of the preceding claims including means for rendering safe the potential source of ignition by applying a high-pressure purge to the interior of the inner enclosure.

7. An explosion protection system as claimed in any one of the preceding claims in which the second sensor is positioned between an outer enclosure, which shields the inner enclosure, and the outer enclosure.

8. An explosion protection system as claimed in any one of the preceding claims in which the second sensor is sensitive to the level of one or more explosive gases present.

9. An explosion protection system as claimed in any one of the preceding claims in which the second sensor is sensitive to the level of explosive dust present.

10. An explosion protection system substantially as specifically described, with reference to the drawing.