This invention relates to respiratory protection devices of the type having chemisorptive property and in particular to means of providing an indication of the condition of the chemisorptive properties and whether such properties have been exhausted so as to make respiratory protection inadequate.

BACKGROUND OF THE INVENTION

Respiratory masks using replaceable filter cartridges are commonly used for protection against a wide range of respiratory hazards which include material that is toxic or simply causes discomfort The filter cartridges are replaced when the chemisorptive material is exhausted and no longer provides respiratory protection at or below hazardous concentration levels that become apparent to the user or is otherwise arbitrarily or administratively determined. Often that level is determined only by the user sensing that the offending material has entered the mask. For some materials even that level of exposure constitues a hazard.

It is desirable to have a means of indicating the exhaustion of the media which clearly indicates the efficacy of the chemisorptive medium well before the offending material enters the mask, so that the user of the respiratory mask is not placed at risk or discomfort. Preferably however the indication should not be too much in advance of exhaustion of the chemisorptive medium because otherwise the chemisorptive medium is used inefficiently.

For simplicity it may be desired to provide a simple chemically reactive colour indicator such as potassium permanganate impregnated alumina granules.

A thin peripherally disposed layer of chemically reactive indicator does not suffice to give a reliable colour indication and the depth of the indicator must be sufficient to provide effective contact with the gas passing therethrough. On the other hand, for a simple respiratory mask to which the filter cartridge is connected rigidly, the depth that is available is restricted in that it must not interfere with the operation of the mask. As the mask is extended then the weight of the filter cartridge has a greater effect on the wearer, causing greater discomfort, to the wearer as well as giving rise to a greater danger of the seal between the mask and die face of the wearer breaking, allowing unfiltered air to enter the stream being breathed by the user of the respirator mask. Additionally there is a greater likelihood of the filter cartridge being more likely to knock against adjacent articles, the whole arrangement being somewhat ungainly.

It may be possible to simply provide for a visualisation chamber within a filter cartridge for a mask, however, the indicator can only be visualised from a periphery of the filter, and a difficulty would arise in that the majority of air flows through the centre of the filter cartridge, accordingly the indicator would have a tendency to delay showing that the filter is exhausted. Additionally this would have d e draw back of adding to the cost of producing the filter, and the complexity of changing an automated assembly system, to provide for an additional layer including either the cost of a layer of indicator material across the depth of the chamber or the provision of an off-centre indicator chamber. Furthermore currently produced filter cartridges, having no in built indicator means could not be used.

There have been several proposals for indicators for respiratory filters, two of which are given by way of example. Thus US patent 1725893 by Yablick discloses a gas mask canister, with a window along one side of the canister, and an indicator medium located peripherally of the canister adjacent the window. US patent 4530706 is a more recent proposal discloses a peripherally located, multi-tiered compartment visible from an indicator window, constructed so that several different indicators can be one in each of the compartment so that the effectiveness of the unit to filter a number of compounds can be assessed and having a molecular sieve filter upstream of the indicator.

An object of this invention is to provide a cultivation apparatus that obviates or minimises at least one of the aforementioned problems in a simple yet effective way, or at least provides the public with a useful choice.

SUMMARY OF THE INNENΗON

In one form, although not necessarily the only or the broadest form, the invention could be said to reside in the combination of a respiratory mask and filter, the mask being of the type adapted to be fitted to the face of a user, and including an inlet attachment for attachment of the filter, the filter being of the type including a filter housing encasing a chemisorptive bed, with one inlet on one side for the entry of external air, and an outlet with a connection for attachment to the mask inlet attachment, an indicator module including a housing of rigid material including a transparent window extending through the housing including two open ends, a first of the open ends attached to the mask inlet, and a second attached to the filter outlet, said indicator housing including indicator bed in an air passageway connecting said mask and the filter, to indicate the efficacy of the chemisorptive bed, a cross-sectional dimension of the passageway being restricted at

least at said window with respect to the cross sectional dimension of the chemisorptive bed.

The restriction at the window is to ensure that gas passing through the filter has a relatively uniform effect on the indicator within the indicator module so that visualisation of a result is reliable for the condition of the chemisorptive bed. Furthermore because of the contriction of the indicator module their is greater contact of the indicator to air that for the chemisorptive bed, thereby giving a somewhat conservative indication of the condition of the chemisorptive bed

The indicator medium might be an activated alumina which is impregnated with potassium permanganate as an indicator. It is to be understood that other indicator media can equally be used, and the choice is in part dependent on the material which is desired to be filtered. The colour of the indicator in the activated alumina granules can be compared against a colour chart to determine the condition of the chemisorptive bed. The colour chart may be fixed on the outside of a casing enclosing the filter to enable easy checking of the state of the indicator in the chemisorptive medium.

For simplicity of manufacture the indicator housing is transparent in its entirety so that, for example, the housing may be formed from a transparent plastics material.

In an alternative form the invention might be said to reside in an indicator module for use with a respiratory mask and a filter, the mask being of the type adapted to be fitted to the face of a user, and including an inlet attachment for attachment of the filter, the filter being of the type including a filter housing encasing a chemisorptive bed, with one inlet on one side for the entry of external air, and an outlet with a connection for attachment to the mask inlet attachment, the indicator module including a housing of rigid material including a transparent window extending through the housing including two open ends, a first of the open ends attached to the mask inlet, and a second attached to the filter outlet, said indicator housing including indicator bed in an air passageway connecting said mask and the filter, to indicate the efficacy of the chemisorptive bed, a cross-sectional dimension of the passageway being restricted at least at said window with respect to the cross sectional dimension of the chemisorptive bed.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding the invention will now be described with reference to the accompanying drawings wherein

FIG. 1 is a part perspective view of a first embodiment of an indicator module attached to a filter cartridge and mask with the indicator housing shown in part cutaway,

FIG. 2 is a somewhat magnified sectional view of the indicator module showing component parts,

FIG. 3 is a part perspective view of a second embodiment of an indicator attachment in place between a filter cartridge and a mask, with the indicator housing shown, in part, cutaway.

DETAILED DESCRIPTION OF THE DRAWINGS

Similar reference characters indicate corresponding parts throughout the several views of the drawings.

Dimensions of certain of the parts as shown in the drawings may have been modified and/or exaggerated for the purposes of clarity of illustration.

The drawings show generally a respiratory mask 1 attached to a replaceable filter cartridge 2 via an indicator module 3. The respiratory mask is of a standard type that may simply fit over the nose and mouth of the user, or may be more extensive to protect the eyes of the user as well. The mask is generally constructed of a gas impermeable material such as a synthetic rubber, however with an inlet 4 being reinforced so as to be supported away from the face of the user, and sufficiently strong to support the weight of the filter cartridge.

The filter cartridge 2 is generally of a rigid construction, and includes a housing 5 constructed either from a rigid plastics material or thin coated sheet metal. The details of the filter used is not shown but it generally comprises a mechanical filter of a non¬ woven fibrous material or an open cellular foam supported behind a mesh, and downstream of the mechanical filter is positioned a chemisorptive bed. The filter generally has means to keep the chemisorptive bed in position from either end of the cartridge. At the inlet 6 that might be by means of the mesh together with the mechanical filter. Although separate means may also be used, such as by a woven fabric positioned downstream of the mechanical filter. The chemisorptive material may vary depending upon the type of pollutant that it is desired to filter out, and for general use that might be an activated carbon. This gives a general indication of the type of filter toward which this invention is directed, however, other configurations are available or may become available, and it is to be understood where there is a filter with

a depletable chemisorptive compound and an indicator exists that reflects its condition then this invention applies.

The outlet of the filter 7 is formed so as to provide a rigid connection with the inlet of the mask 4, and in the illustrated embodiments this is achieved by a screw threaded fit.

The indicator module is formed so as to take advantage of the connection means already provided, and has a complementary screw threaded oudet 8 adapted to fit to die inlet of the mask, and a screw threaded inlet 9 adapted to fit to the outlet of the filter cartridge. The indicator housing 10 is formed from a transparent plastics material, in its entirety, so that the interior can clearly be seen. Potassium permanganate impregnated alumina granules 11 are held in the indicator module at eiti er end by a press fitted mesh 12 and an open cellular foam 13. The indicator granules are tightly packed so that in use the granules do not settle and allow passage of gas without contacting the granules. The open cellular foam acts in part to prevent passage of fine material, it also however acts to slow down the air passing into the indicator module so that a greater volume of the chemisorptive material within the filer cartridge is utilized.

The potassium permanganate content of the activated alumina is 5% by volume and contains no more than 5 mg per cubic metre respirable dust

The dimensions of me indicator module are such that they reflect a constriction of the passage through the filter. The cross sectional dimensions of the indicator bed witiiin the indicator module is restricted relative to the cross sectional dimensions of the filter. This ensures that firsfly there are no reductions of airflow through the periphery of the indicator, and secondly that there is a greater passage of air through the indicator as compared to the chemisorptive bed of die filter cartridge.

The dimensions of the indicator bed within the indicator module is approximately 1.5 cm in diameter, and approximately 2.5 cm in depth. It is found that this dimensions give an accurate indication of die condition of die chemisorptive bed of the commercially available replacement filter cartridges. Some experimentation has found tiiat this may also vary dependent on the packing, to down as low as about 2 cm. It is found that an addition of about 2.5 cm does not make the mask particularly cumbersome, however that will naturally also depend upon die design of mask that is used. It is envisaged that an additional depth of about 0.5 to 1 cm may still be give quite a useable mask.

In the second illustrated embodiment shown in FIG. 3 the screw fittings have a much greater diameter, being standard for that type of fitting. The indicator housing accordingly includes two flared portions 14 and 15, which can be screw threaded to d e respective inlet and oudeL