GB2382593A

GB2382593A - A working enclosure providing a clean air zone in hazardous environments

Info

Publication number: GB2382593A
Application number: GB0128534A
Authority: GB
Inventors: Daniel Alexander Constantinis
Original assignee: E M & I
Current assignee: E M & I
Priority date: 2001-11-29
Filing date: 2001-11-29
Publication date: 2003-06-04
Anticipated expiration: 2021-11-29
Also published as: GB0128534D0; GB2382593B; CA2426638C; CA2426638A1

Abstract

A working enclosure comprises a canopy 10 supported by a frame 11 with a skirt 12 to be held in close proximity with the contact surface. Magnetic pads 13 are provided to enable attachment of the enclosure to a metallic surface. A supply of clean air from a fan 23 is supplied to the interior of the canopy by an inlet duct 20 and maintained at a slight over pressure therein by controlled discharge from an outlet duct (Fig 2 item 30). The supply of clean air is monitored to detect contamination and the operation automatically shuts down the supply of air when the contamination alarm is raised. The pressure inside the enclosure is maintained when an operator enters or leaves by the provision of an air lock (Fig 2, 33).

Description

A WORKING ENCLOSURE THIS INVENTION concerns a working enclosure adapted to provide a clean air zone within a potentially hazardous environment.

The invention is particularly though not exclusively concerned with the provision of a clean air zone in the form of a habitat within which so-called"hot work"may be carried out. Hot work may be deemed to be any activity which has the potential to introduce a source of ignition into a zone which may contain a gas and air mixture within a flammable range. The lower limit of such a range may be defined as the concentration below which there is insufficient flammable gas to support combustion and the upper limit may be the concentration above which there is insufficient air to support combustion. Such work is often carried out in vessels adapted to contain gas or flammable liquids such as the oil storage tanks of crude oil carriers. It is sometimes necessary, to carry out, when such vessels are empty, repair work on parts of the internal structure. This work may involve welding or cutting, and residues of gas and oil can cause an explosion when a source of

ignition is introduced into such a potentially hazardous environment.

Patent specification No. GB 2311847 describes a working enclosure adapted to provide a clean air zone within a potentially hazardous environment, the enclosure comprising a canopy adapted to cover at least a part of a working surface to define therewith a clean air zone, at least one inlet duct connecting said zone to a supply of clean air, means to monitor the content of the air supplied to said zone, and alarm/shut down means responsive to the monitoring means.

The term"clean air"is to be construed as including either fresh clean air which is free of acutely inflammable gases, or for example, a mixture of clean air and an inert gas.

According to the present invention such a working enclosure is improved by the provision of means to discharge air from the enclosure to establish a controlled operating air pressure within the enclosure.

The discharge means may be a duct having a diameter less than that of the clean air inlet duct.

The operating air pressure within the enclosure may be controlled within the range of 0.1 to 0.3 bar above ambient pressure outside the canopy.

An air lock may be provided in the canopy wall to enable operator access without substantially affecting the operating air pressure within the canopy.

Means may be provided to direct air circulation around the interior of the canopy thus to ensure substantially complete scavenging of any contaminant gases therefrom.

The canopy may be provided in the form of a flexible shroud or a rigid enclosure or bubble.

Preferably, the canopy also includes means whereby the edges of the canopy may be maintained in close relationship with the working surface.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which :- Fig. 1 is a perspective view of a working enclosure as described in specification GB 2311847 and occupied by an operator in readiness to carry out work on a vertical surface within, for example, an emptied oil tank; Fig. 2 is a schematic elevation of a working enclosure made in accordance with the invention and located against a vertical wall; and Fig. 3 is a schematic elevation of a modified form of enclosure when located against a horizontal surface.

The canopy 10 made from, for example, a durable material such as nylon, pre-treated or lined with a fire prevention substance or blanket, is supported by a frame 11 and has a

peripheral skirt 12 adapted to locate closely against a working surface to which the device may be applied and retained by magnetic pads 13. The canopy is supported from above by rigging ropes 14 and 15. A salable access flap 16 is provided through which an operator 17 may enter and leave the enclosure. One or more suspension lines 18 to support the operator, pass into the canopy 10 through a generally sealed aperture 19 at the top of the canopy. Thus the enclosure is located temporarily in a fixed position against the working surface and in substantially sealed engagement therewith by means of the skirt 12, the flap 16 and the aperture 19.

An air inlet duct 20 is connected to the canopy wall and communicates with the interior of the enclosure. The duct is preferably made from a flexible material and passes upwardly out of the hazardous environment, for example, through an aperture in a decking panel 21 and is supported above same by a frame 22 at the upper open end of which there is provided a fan 23 supplying air through the duct 20 into the enclosure. The fan 23 is associated with a sensing or monitoring device (not shown)

which is further associated with an adjacent or remote alarm ! shut down system for a purpose to be described.

Within an enclosure as described the operator may carry out welding, cutting or similar operations without the risk of causing an explosion since clean air is ducted into the enclosure at a slight over-pressure thus bleeding from the flap 16 and aperture 19, and around the skirt 12.

The upstanding frame 22 ensures that the fan supplying clean air is disposed well above the deck 21 and any low-lying gases which may be present.

The sensing or monitoring device associated with the fan 23 is adapted to detect the presence of a toxic or inflammable contaminant in the air being supplied to the enclosure, and if present will either sound an alarm to alert the operator or other staff thus to discontinue the hot work, or to shut down the supply of power to whatever hot work tools are being used in the enclosure, or simply to shut down the fan supplying the contaminated air to the duct 20.

When the working surface upon which the hot work is being carried out is located between two potentially hazardous zones, for example, when repairing a bulkhead separating two hydro-carbon storage tanks, a second enclosure similar to that described may be positioned on the opposite side of the bulkhead whereat local heating of the working surface may otherwise create an explosive condition.

Referring now to Figs. 2 and 3 which schematically illustrate an improvement in accordance with the present invention, Fig. 2 depicting the working enclosure located against a vertical surface, and Fig. 3 depicting the enclosure against a horizontal surface, there is provided a discharge duct 30 in communication with the interior of the canopy at a position remote from that at which the air inlet duct 20 is connected. The diameter of the discharge duct 30 is less than that of the inlet duct 20 thus to ensure a controlled over pressure within the canopy, of between 0.1 and 0.3 bar above ambient pressure outside of the canopy. If required, an adjustable constriction of pipe 30 may be provided whereby the rate of discharge of air there through may be selected.

A baffle 31 within the canopy directs air circulation around the interior of the canopy as indicated by arrows 32. This ensures substantially complete scavenging of any contaminant gases therefrom.

Thus, by controlling the discharge of air from the canopy as opposed to the expedient of allowing it to bleed through the aperture 19 as in Fig. 1 or around the skirt 12, maintains a controlled amount of air over pressure within the canopy thus avoiding discomfort for personnel within the enclosure or insufficient pressure to ensure correct operation thereof.

An air lock 33 is attached to the wall of the canopy to enable operator access without substantially affecting the operating air pressure within the canopy.

Referring now to Fig. 3 there is shown an alternative configuration for the enclosure when located on a horizontal working surface. In this example, the air inlet and discharge ducts are connected to one end wall of the canopy while the access air lock is located on the opposite end wall.

It is not intended to limit the invention to the above details. For example, the canopy 10 may be produced in the form of a rigid pre-shaped enclosure, and the air lock 33 may be omitted in an application where the canopy is to be disposed over a horizontal surface and lowered into place with an operator already in position. Indeed, the form of the enclosure may differ in many respects depending upon the application and location of the work to be carried out.

Claims

1. A working enclosure adapted to provide a clean air zone within a potentially hazardous environment, the enclosure comprising a canopy adapted to cover at least a part of a working surface to define therewith a clean air zone, at least one air inlet duct connecting said zone to a supply of clean air, means to monitor the content of the air supplied to said zone, and alarm/shut down means responsive to the monitoring means; characterised by the provision of means to discharge air from the enclosure to establish a controlled operating air pressure within the enclosure.

2. A working enclosure according to Claim 1, wherein the discharge means is a duct having a diameter less than that of the clean air inlet duct.

3. A working enclosure according to Claim 1, wherein the operating air pressure within the enclosure is controlled

within the range of 0.1 to 0.3 bar above ambient pressure outside of the canopy.

4. A working enclosure according to any preceding claim, including an air lock in the canopy wall to enable operator access without substantially affecting the operating air pressure within the canopy.

5. A working enclosure according to any preceding claim, including means to direct air circulation around the interior of the canopy thus to ensure substantially complete scavenging of any contaminant gases therefrom.

6. A working enclosure according to any preceding claim, wherein the canopy is in the form of a flexible shroud supported by a frame and having a peripheral skirt adapted to locate closely against the working surface.

7. A working enclosure according to any preceding claim, wherein the canopy has a non-flammable internal surface.

8. A working enclosure according to any preceding claim, wherein the canopy is disposed upright, supported by rigging ropes.

9. A working enclosure according to any preceding claim, wherein the air inlet duct includes an open end to which is connected a fan supplying the air through the duct into the enclosure, the duct being supported by a frame at its open end at a position remote from the canopy.

10. A working enclosure according to any preceding claim, wherein the alarm/shut down means is adapted to shut down the supply of power to hot-work tools when used within the enclosure.

11. A working enclosure according to Claim 1, wherein the canopy is in the form of a rigid pre-shaped enclosure.

12. A working enclosure according to any preceding claim, including a plurality of magnetic pads attached peripherally to the canopy to maintain it in close proximity with the working surface.