Background to the Invention

This invention relates to an entrance chamber for a contamination control enclosure of the type which may be used with or without a negative pressure environment in the contamination control enclosure, such as may be required when a contamination control enclosure is provided for retaining hazardous substances or materials within the enclosure.

There are often situations in which a contamination control enclosure is required. These include:

• The removal of hazardous materials or chemicals from buildings where release into the surrounding environment would be undesirable and would therefore need to be controlled, e.g. asbestos removal; • Containment of substances such as genetically modified seeds which need to be retained in an enclosed portion of a building to prevent them being transmitted to the outside environment.

The most common approach to handling such situations is to create a negative pressure enclosure within the building. This may be a room within a building which is sealed to the rest of the building and has an extractor with a fine filter fitted to it, to remove air. Clean air is drawn into this enclosure and air is filtered before being released into the environment by the extraction. The weak point of any such enclosure is the point of entry into the enclosure. Under normal operation, because the air is being drawn in as a result of the negative pressure, contaminants are not released through the entrance. However, if the negative pressure generating equipment fails through either technical or human error, a backdraft can cause contaminants to be released through the entrance, as can the passage of personnel through the entrance.

Summary of the Invention

Preferred embodiments of the present invention seek to overcome this problem by restricting any reverse air flow which may result from the loss of negative pressure whilst still enabling personnel to enter or leave the enclosed area with minimum release of contaminants.

Embodiments of the invention may also be used without a negative pressure environment.

A preferred embodiment of the invention provides an entrance chamber for a contamination control enclosure comprising an impervious flexible tent sealable to an entrance to a contamination control enclosure and supportable by a substantially rigid frame, the tent comprising at least one chamber with an opening at each end, each opening having a surround and a hanging flap of a larger area than the opening on the enclosure side of the surround and which hangs adjacent to the surround in the absence of any pressure differential across the opening.

The frame may be made from metal or plastics type material.

The tent may be made from any impervious fabric.

The tent may be manufactured from plastics material such as polythene.

The tent may be disposable.

The tent may be fire retardant.

Preferably the tent is constructed such that it hangs from the frame and the frame is not exposed to the interior of the tent.

Preferably the tent is of a single piece of construction with sealed seams to prevent contaminants passing through any joins.

The tent may be constructed as a plurality of chambers each separated by a corresponding opening and surround and a vertically hanging flap.

Brief Description of the Drawings

Preferred embodiments of the invention will now be described in detail by way of example with reference to the accompanying drawings in which: Figure 1 shows a frame assembly for use in an embodiment of the invention; Figure 2 shows the frame of figure 1 slotted through external loops formed in a tent embodying the invention; Figure 3 shows a side view of an embodiment of the invention with a negative pressure environment in the enclosure to which it is connected; Figure 4 shows a side view of an embodiment of figure 3 with a failure in the negative pressure environment; Figure 5 shows an embodiment of a hanging flap and the opening against which it bears; Figure 6 shows an embodiment of the tent using hook and loop straps and clips for attachment to the frames; Figure 7 shows an alternative arrangement for attaching the tent to the frame using resiliently stretchable suspension fixings, and; Figure 8 shows a frame for an alternative embodiment comprising a hinged collapsible unit.

Detailed description of Preferred Embodiments

Figure 1 shows a frame comprising a plurality of straight, square or round or rectangular tubes of 2 of metal or plastic, connected together using metal or plastic joints 4 to form a rigid structure 6. The frame may also be provided as a pre-fabricated rigid structure. The frame when constructed comprises two or more rectangular sections 8 spaced from each other by substantially rigid spacing members 10. This material used for the frame may be resiliently flexible material to enable it to be bent when it is packaged for transportation.

In figure 2 a tent is shown connected to the frame of figure 1 by slotting the frame tube through loops 12 as the frame is constructed. The loops are formed on the outside of the tent as the frame is assembled. Each section 8 of the frame passes through a loop in the exterior of the tent. The spacing members 10 may also optionally pass through additional loops. The tent is formed from a tube of flexible material such as polythene or from a plurality of panels of polythene which are connected with impervious seals, such as welded seals or glued seals. Each section 8 of the frame supports, via its attachment to the tent, a vertically hanging flap 16. The vertically hanging flaps may be formed from material of sufficient density to cause them to hang substantially vertically, or alternatively may be of a lighter weight material such as polythene with weights attached to the free end of each flap to cause it to hang substantially vertically.

Figure 3 shows a side view of the entrance chamber in operation. The right hand end of the unit is imperviously sealed to the negative pressure enclosure to which it is to form an entrance an exit. This is done using impervious tape. A sheet of e.g. polythene is preferably sealed first to the entrance and the entrance chamber is then sealed to that sheet, and an opening is cut in the sheet. A flange of impervious material is attached to the end of the chamber and is fixed to the sheet of polythene with impervious tape. Because there is a negative pressure differential between the enclosure on the right hand side of the entrance/exit chamber and the exterior there is an air flow into the chamber. This causes the four flaps shown in this embodiment to move in the direction of the air flow, thereby permitting air to enter the negative pressure enclosure by lifting the flaps from the vertical position.

When there is a failure of the negative pressure environment, the flaps hang down substantially vertically as shown in figure 4. The reverse air flow causes the flaps to be pushed closed against the surrounds of the openings they are intending to close, thereby preventing the escape of contaminants. An example of a flap 16 and the opening 20 against which it closes is shown in figure 5. As can be seen, the flap 16 has a greater area than the opening and therefore it can bear against the surrounding of the opening to close it. The flap is suspended from substantially the same position as the attachment of the surround to the top of the tent or to a position on the surround above the opening, but in a place substantially adjacent to the place of the opening. The opening 20 and its surround may be positioned at an inclined angle with the top further from the enclosure than the base in the tent with the hanging flap suspended from the top of the surround. In such a situation the weight of the flap will cause it to bear against the surround with more force than it would with a vertical surround, thereby improving the resistance to contaminant release in the event of failure of the negative pressure environment and also make the entrance chamber more suitable for protecting enclosures which do not use negative pressure. The hanging flap may be sealed by welding to the tent during manufacture, or alternatively may be provided with an adhesive strip and may be fixed to the tent when it has been positioned on its frame.

An example of the tent suspended using hook and loop fixings and clips is shown in figure 6. These form straps 22 which pass around the frame and are then connected together thereby suspending the tent from the frame.

An alternative method for attaching the tent to the frame is shown in figure 7. This uses stretchable and non-stretchable suspension fixings 24 which hook onto the frame.

Figure 8 shows an alternative frame construction using connected hinged elements. This enables erection and deconstruction from a single complex unit rather than individual tubes. Frame sections are connected by hinges 26. Some form of hook or loop or suspension fixing must be used with such a frame to suspend the tent since the elements of the frame are unable to pass through external loops in the tent.

In use, when the negative pressure system is working, the vertically hanging flaps shown in figures 3 and 4 are drawn into the negative pressure environment. If the negative pressure fails, the doors are no longer drawn inwards and hang vertically. Any positive pressure towards the external environment causes the flaps to bear against the plastic surround 20, thereby restricting the release of contaminants.

Preferably multiple chambers are provided in the entrance to enable safe entry and exit from the building. This is preferably improved by ensuring that the entrance and exit from each chamber are sufficiently spaced to enable one flap to close before the next opens, when a person passes through. A single chamber may be provided with a vertically hanging flap and a corresponding opening at each end. The examples shown in this description show three chambers. The tent may be a disposable unit for use in temporary applications such as removal of asbestos from a portion of the building. This prevents the need to clean the tent and it can be disposed of by suitable methods.

The tent may be formed of fire retardant material.

The tent and frame can be supplied separately with disposable units being put on the frame as required.

The embodiments show the entrance being provided in a straight line. In some circumstances, it may be preferable to provide e.g. an L-shaped entrance and this can be easily constructed on the same principles as the embodiments shown.