There has for some time been a dilemma in the handling of sterile or toxic materials in contained facilities. The normal practice in the U. K. has been to place such materials in a negative pressure enclosure. This has the advantage of ensuring that any leakage in the chamber would be inwards, thus containing the toxic material. This approach met with the approval of safety officers and authorities but may compromise the sterility of the product.

The risk to sterility is considered to be of importance for such products as chemotherapy drugs, where a non-sterile product would put at risk the patient. To eliminate the potential of contaminating the product during handling in the containment system it should be run at positive pressure, so that any leaks would be outwards, thus protecting the product from external contamination. Thus, negative pressure is required to protect the operator and positive pressure is required to protect the product. These types of enclosures are described in a code of practice 1 published by the U. K.

Stationary Office. In some European countries, especially France, the risk to the product is considered to be more important than the risk to the operator, so containment systems for sterile toxic materials are generally operated at a small positive pressure. In the U. K. the risk to the operator is considered to be more important. Hence, in the U. K., sterile toxic materials are generally handled under negative pressure.

There are many different types of construction of containment systems, normally called isolators. They will vary in the materials of construction from flexible wall devices manufactured from flexible PVC film to rigid isolators manufactured from stainless steel. The type of construction will depend on the frequency of use and the demands of the process and operators. Isolators also have different types of airflow patterns, which

will either be turbulent or laminar flow. Turbulent flow systems are generally cheaper as they do not require the same volume of airflow, and hence the air handling equipment is smaller. Laminar flow isolators are usually more expensive but because of the higher airflow rates will reach the required internal air quality much quicker.

To maintain cleanliness inside an isolator the air is filtered both as it enters and as it leaves. For isolators that are to be used for sterile manipulations the air is generally filtered twice before entering the chamber, and only once prior to leaving the chamber. The filtration technique is changed for isolators that are used for the handling of toxic material, by using a single filter on entry and a double filter at the exit.

An object of the invention is to overcome the problems of handling sterile or toxic materials in a positive pressure containment box.

This invention provides a closed cabinet for toxic or sterile material having a work station within the cabinet to receive toxic or sterile material, means to enable an operator to conduct contactless operations on the material, means to provide a flow of filtered air through the cabinet at an elevated pressure above ambient to prevent ingress of contaminant material to the cabinet and means to cause said pressurised air to flow over the work station in a direction away from the side of the cabinet which the operator functions to protect the operator from exposure to toxic material.

The arrangement according to the invention can be regarded as a complex laminar flow device, in which the direction of the laminar airflow is changed inside the chamber. It is, perhaps, more accurate to describe the airflow as unidirectional at any one point in space inside the isolator.

The description of unidirectional, where applied to airflow implies that the air is travelling in the same direction, but not necessarily all of the air is travelling at the same velocity. Truly laminar airflow is not only unidirectional, but will also have the same velocity at all points in a cross- section of the flow.

By generating a unidirectional flow of filtered air from the top of the Isolator in a downwards direction; at an average velocity of between 0.1 and 0.3 m/sec, the air within the Isolator will be changed very frequently, and hence any airborne particles will be swept away.

Normally, in prior art cabinets it would be expected that the air would be extracted from or near the base of the Isolator, thus maintaining the near laminar flow until the air reaches the base of the Isolator.

Such cabinets may be operated at either positive or negative pressure, and will usually have gloves that penetrate a window in the front face of the cabinet for the operator to conduct manipulation of the materials at the work station inside the cabinet.

The present device places the extract of the air from the cabinet, not in the base, but in the rear wall. The air is then extracted through filters placed in the rear wall. Deflector vanes are placed inside the chamber to ensure that the airflow patterns are correct. One deflector vane is placed in the top of the chamber to ensure that the air moves down the front of the chamber and then across the base. A second vane is placed at the rear to prevent the air taking the shortest route from the top to the rear filter.

This arrangement of having the air delivered to the cabinet at the top, and extracted at the rear, causes the air to be swept to the rear of the chamber at the working zone. The air movement at the working zone towards the rear of the Isolator, ensures that any material is swept away from the operator, protecting him/her by the movement of the air, whilst the product remains protected by the positive pressure.

With the type of airflow patterns described it is important that the internal chamber pressure is maintained at a low level of about 35 Pascals. This is most easily achieved by using a two-fan system, one fan supplying air and one extracting air. Such"push-pull"systems require dynamic control and are balanced by using one to control the pressure and the other to control the flow. The fan controlling the pressure is made to react quickly

to any change while the fan controlling flow reacts only slowly. This difference in reaction time ensures that the fans do not unbalance each other.

Because of the critical nature of any leaks an automatic test facility has been built into the program. This performs a leak test on the whole system prior to the commencement of any work, and will not allow work to start until a satisfactory leak test has been completed.

The following is a description of a specific embodiment of the invention, reference being made to the accompanying drawing which is a diagrammatic view of a cabinet or isolator for the handling of toxic or sterile material.

Referring to the drawing, there is shown a cabinet for isolator indicated generally at 10 for handling toxic or sterile materials. The cabinet has a base wall 11, top wall 12, inclined front wall 13, back wall 14 and side walls 15. A work station indicated generally at 16 is provided above the bottom wall 11 where toxic or sterile materials are supported Front wall 13 of the cabinet has a window 17 for an operator to view the materials at the work station and has gloves 18, the cuffs 19 of which are mounted in ports 20 in the window. The gloves project into the cabinet behind the window for an operator to use to manipulate the materials of the work station without direct contact therewith.

A pump or pumps (not shown) of conventional construction are provided for delivering an airflow to the top of the cabinet. Air enters the cabinet through a port 22 in which a high efficiency particulate air filter 23 is mounted having an efficiency of at least 99.997% when tested in accordance with British Standard 3928. Other grades and deficiencies of a filter may be used according to the type of containment required.

Filtered air flows downwardly from the inlet in the directions of the arrows 24.

An air deflector 25 is mounted on the underside of the top wall of the

cabinet to deflect a flow of air downwardly over the inclined front wall of the cabinet as indicated by the arrows 26. The rear wall of the cabinet has an outlet port 27 towards the lower end thereof in which a further high efficiency particulate air filter 28 is mounted to filter air exiting from the cabinet. A second air deflector 29 is mounted on the inside of the rear wall of the cabinet to extend from the upper end of the outlet port diverging away from the port towards the bottom of the cabinet to provide an entry indicated at 30 to the outlet port which is open towards the bottom of the cabinet. Air flowing downwardly from the inlet port in the direction of the arrows 26 over the front window of the cabinet passes over the operator gloves and thence turns as it reaches the lower part of the cabinet to flow towards the rear of the cabinet over the work station and through the entry 30 to the outlet port 27. The positioning of the inlet and outlet ports coupled with the air deflectors thus ensures that there is a stream of air moving through the cabinet away from the front wall of the cabinet from where the operator views and acts on the contents of the cabinet at the work station. The air patterns created thus ensure that airborne material generated in the working zone is swept away from the operator keeping him safe from contamination whilst the project is projected by the position pressure of the air.

The pump or pumps provided air flow through the cabinet are controlled conventionally to maintain the required pressure balance in the cabinet.

As indicated earlier, the cabinet or isolator may be used for either toxic or sterile materials.

The air patterns thus ensures that air borne material generated in the working zone is swept away from the operator keeping him safe from contamination, whilst the product is protected by the positive pressure.

It will be appreciated that many modifications may be made without departing from the scope of the invention. For example, the apparatus may be used for handling sterile material instead of toxic materials.