Respirators

Abstract

A respirator for use in noxious atmospheres comprises a hood which completely covers the head of the wearer and the edge of which extends around his neck or shoulders and a mechanical blower is fitted to the inlet connection so as to provide more air than required for respiration to provide a positive internal pressure. The respirator may also serve as an oxygen mask for use at high altitudes by airmen and preferably includes a separate oro-nasal mask in which case the inlet has two branches, one passing to the mask by way of a non-return valve and the other passing to the interior of the hood also through a non-return valve. When oxygen is being supplied a valve operates to prevent the flow of air from the blower to the mask.

Description

Respirators for use in noxious atmospheres of fumes or poisonous gases normally have a face piece which is intended to form a close seal with the face of the wearer but in practice seldom does. It is extremely difficult to form an effective seal between the edge of the face piece and the face of the wearer and there is thus always the risk that some of the surrounding atmosphere may be drawn in between the face and the face piece instead of through the filtration canister.

According to the present invention, a respirator comprises a hood which completely covers the head of the wearer and the edge of which extends around his neck or shoulders and a mechanical blower is fitted to the inlet connection so as to provide more air than required for respiration, so that in use some at least of the excess flows outwardly between the edge of the hood and the neck or body of the wearer. Although the edge of the hood may not make a good seal with the neck or body of the wearer, this is of no consequence in view of the excess air provided by the blower. In other words, the respirator operates at a positive pressure and the outwardly flowing excess air positively prevents any inward flow from the atmosphere. In addition, the excess air prevents the window of the respirator from becoming misted up, while the provision of a hood over the whole of the head of the wearer provides a further protection against airborne contaminants.

The respirator preferably includes a separate oro-nasal mask which fits closely round the mouth and nose of the wearer, in which case the inlet needs to have two branches, one passing to the mask by way of a non-return valve and the other passing to the interior of the hood, also through a non-return valve. Thus the air which is inhaled is exhausted from the mask through a separate outlet fitted with a non-return valve, while only the excess air which provides the positive pressure passes outwardly around the neck of the wearer.

A construction of the same general type can be adapted so that it can serve also as an oxygen mask for use at high altitudes by airmen. For this purpose a separate oxygen supply line needs to be included together with a valve which, when oxygen is being supplied, operates to prevent flow of air from the blower to the mask. When this form of the respirator is to be used at low altitude, no oxygen is required and the respirator therefore merely functions as previously described, the incoming air being shared between the inlet to the mask and the inlet to the interior of the hood. When operating at high altitudes with the oxygen supply connected, the valve operates to close the air inlet from the blower to the mask so that all the air provided by the blower passes to the interior of the hood and then outwardly as previously described.

The valve just referred to preferably cooperates with a seating against which it is pressed to allow air to flow through it from the blower to the mask when no oxygen is being supplied, and a main spring is brought into action by the oxygen pressure when the latter is connected so as to hold the valve more firmly on its seating against the pressure of air from the blower. The inlet connection to the interior of the hood from the blower remains open under all circumstances. If, when no oxygen is being supplied, the blower fails, the wearer of the respirator can merely draw in air through the filtration canister and this air is allowed to pass freely into the mask through the valve.

When operating at high altitudes with the oxygen supply connected the oxygen pressure brings the main spring into action so that the valve is held closed against the flow of air from the blower, all of which thus passes to the interior of the hood, the oro-nasal mask being supplied with oxygen by way of a normal oxygen regulator. If, under these conditions the oxygen supply fails, the suction caused by respiration of the wearer is sufficient to open the valve even against the effects of the main spring to allow air to flow from the blower. This air will not have sufficient oxygen content for normal respiration purposes but the difficulty in breathing experienced by the wearer due to the effort necessary to open the valve against the main spring serves as a warning of the failure of the oxygen supply before anoxia sets in and thus enables him to turn on the emergency oxygen supply or to take other remedial measures.

As an alternative to the valve just described, i.e. one which has basically two separate operating conditions, it is also possible to use a valve having three separate operating positions. This valve needs to be fitted at the point where the inlet connection to the hood branches and when the respirator is used at low altitude and no oxygen is required, the valve takes up an intermediate position allowing the incoming air to be shared between the inlet to the mask and the inlet to the interior of the hood. When operating at high altitudes with the oxygen supply connected, the valve takes up a position which closes the air inlet to the mask but leaves the inlet to the interior of the hood fully open so that all the air provided by the blower passes to the interior of the hood while the inlet to the mask is connected to the oxygen supply. The third position of the valve is to allow for the possibility of the failure of the blower when the oxygen supply is not connected. If the blower fails when the oxygen is connected, the wearer can breathe oxygen in the normal way and it is only the positive pressure to the interior of the hood which fails. When the oxygen is not connected, however, it is necessary for the wearer of the respirator to draw in air through the filtration canister, after the manner of a normal respirator, and under these circumstances the valve takes up a position in which it closes the inlet to the interior of the hood so that all the air drawn in passes directly to the mask. In this way it is possible to ensure a supply of air for breathing, even though the air for providing the positive pressure may no longer be available.

As mentioned above, the two-condition valve is preferred, in which one of the two conditions is controlled by a main spring. In order to provide the necessary selective control, the valve is conveniently a plate valve and a light spring acts between the plate of the valve and a second plate or similar member, the position of which is controlled by a piston acted on by the oxygen pressure so as to be moved closer to the first plate, thus compressing the light spring and bringing into action the main spring which also extends between the two plates and is shorter than the light spring. When the oxygen supply is no longer required the piston needs to be returned to its initial position by means of a spring and this same effect would therefore occur if there were a failure of the oxygen supply. This would prevent the main spring having the desired effect of making breathing difficult for the user in the event of oxygen failure so as to give warning of anoxia danger. To avoid this risk a spring-operated latch may be provided for holding the piston in the position to which it is moved by the oxygen pressure. When the oxygen supply is deliberately disconnected, this latch can be released manually to allow the piston to return. If the oxygen supply fails, however, the piston will remain latched in position and the necessary warning of anoxia danger will be given.

A construction of respirator in accordance with the invention will now be described in more detail, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is an external view of the respirator showing the various associated components;

FIG. 2 is a diagrammatic view partly in section showing the arangement of valves in the respirator;

FIG. 3 is a sectional view to a somewhat enlarged scale showing an alternative condition of the valve illustrated in FIG. 2; and,

FIG. 4 shows a modification of part of the valve shown in FIG. 3.

Turning first to FIG. 1, the respirator proper is indicated as 1 and is in the form of a hood which fits completely over the head of the wearer and has a flap, part of which is shown as 2 which extends over the shoulders of the wearer and also at the back and front. The respirator includes a harness, part of which is seen at 3 and this also supports a pair of filtration canisters 4 connected by lines 5 to the inlet of a mechanical blower 6. This blower is powered by an electric motor which is normally intended to be supplied via a connection 7 from the aircraft supply. As an alternative, however, a battery 8 is included which is connected to the blower 6 by a quick-release bayonet connection 9. Both the blower 6 and the battery 8 are also supported by the harness 3. The output from the blower 6 passes via a line 10 to the hood which it enters by two separate branches 11 and 12, the first passing to the interior of the hood and the second to an oro-nasal mask 13. The outlet from the mask 13 is shown as 14 but a proportion of the air supplied to the interior of the hood passes outwardly between the flap 2 and the body of the wearer and any other leakage paths which may exist so as to prevent any inward flow from the atmosphere. The remainder of the air passes outwardly through an excess pressure relief valve 15. Other parts also seen in FIG. 1 are an oxygen connection 16, a communcation connection 17 and a test connection 18.

In operation, the blower 6 normally draws air inwardly through the filtration canisters 4 and supplies the air via the line 10 to the two branches of the inlet connection 11 and 12. FIG. 2 illustrates the various valves controlling the inlet of air and oxygen to the interior of the hood 1 and also the outlet valve 14 for air or oxygen from the oro-nasal mask 13. Under normal operating conditions, the air passing along the line 10 splits between the branches 11 and 12, that passing along the branch 11 then passing through a non-return inlet valve 20 and into the interior of the hood 1 to provide positive pressure within the respirator as already described. The air passing into the branch 12 passes through a non-return valve indicated generally as 21 and then via a connection 22 to the mask 13. After respiration the air passes outwardly along a connection 23 and then through a non-return valve 24 to the outlet 14. When oxygen is supplied along the line 16, the valve 21 is effectively closed, as will be described in more detail later, so that all the air from the blower 6 passes along the branch 11 and into the interior of the hood to provide the positive pressure. The oxygen in the line 16 is under high pressure which is reduced to a value suitable for respiration by an oxygen regulator 28 from which oxygen flows to the mask 13 along the connection 22. Oxygen under pressure also flows along a branch line 29 to control the alternative action of the valve 21 as will now be described in more detail.

The valve 21 comprises a plate 30 cooperating wiJh a seating 31 and is normally controlled by a light compression spring 32 which acts between the plate 30 and a second plate 33. Under these conditions the valve acts as a normal non-return valve, thus allowing air from the blower 6 to flow freely through it as indicated by the arrows. In addition to the light compression spring 32 a stronger main spring 35 is also provided which is secured to the plate 33, but since it is shorter than the spring 32, as seen in FIG. 2, it does not normally act on the plate 30 at all and all the control is exerted by the light spring 32 as just described.

When oxygen is being supplied, however, the high pressure oxygen in the branch line 29 passes to the interior of a cylinder 37 within which works a piston 38 to which the plate 33 is secured. The piston is acted on by a tension spring 40 so that it normally occupies the position shown in FIG. 2, but the oxygen pressure applied to the interior of the cylinder 37 overcomes the spring 40 and moves the piston 38 downwardly to the position shown in FIG. 3. This also moves the plate 33 downwardly until the stronger spring 35 comes into engagement with the plate 30 and thus effectively takes over control from the light spring 32. The pressure exerted by the stronger spring 35 is greater than the pressure exerted by the air from the blower 6 so that, under these conditions, the valve 21 remains closed and all the air passes to the branch 11 as described previously.

The piston 38 is provided with a spring-operated latch constituted by a plunger 42 acted on by a compression spring 43 so as to enter a recess 44 in the side of the piston 38. If the oxygen supply is switched off, the plunger 42 is retracted manually by means of a ring 45 also seen in FIG. 1 which allows the piston 38 to return to the position shown in FIG. 2 so that normal operation is resumed. On the other hand, if the oxygen supply fails the piston 38 remains in the position shown in FIG. 3 so that the valve 21 is controlled by the stronger spring 35. Although the pressure developed by the blower 6 is not sufficient to overcome this stronger spring, the wearer of the respirator can nevertheless suck in air through the valve 21, although with difficulty, and the difficulty in breathing thus gives warning of anoxia danger, as previously described.

FIG. 4 shows a minor modification to part of the valve shown in FIGS. 2 and 3, intended to allow for the possibility of failure of the oxygen regulator 28. Although some of the parts are shaped differently from those shown in FIG. 3 the function is the same and corresponding parts are shown by the same reference numerals. In this construction, the position in which the plunger 42 locks the cylinder 38 is such that the end of the plunger does not reach the bottom of the recess 44, but inward movement of the plunger 42 is restricted by a spring clip 50 which engages the wall of the housing shown as 51. The plunger 42 is formed with a portion of reduced diameter constituted by a calibrated notch 52. As shown in the position of FIG. 4 this notch lies just outside the wall of the cylinder 37 but if the plunger 42 is pressed inwardly to the bottom of the recess 44, thus overcoming the effect of the spring clip 50, the notch 52 is brought opposite the opening in the wall of the cylinder 37. This permits a controlled flow of high pressure oxygen from the interior of the cylinder 37 to the entrance to the connection 22 and hence to the mask 13. The flow of oxygen is throttled by the narrow gap between the notch 52 and the opening in the cylinder wall and this has an effect equivalent to that of the oxygen regulator in reducing the pressure of the oxygen to a value suitable for respiration.

By means of the construction just described all the various possible operating conditions can be allowed for. When no oxygen is required, the blower 6 provides air both for respiration and for providing positive pressure. If the blower fails under these conditions, the wearer of the respirator can merely draw in air through the filtration canisters 4, but no positive pressure is provided. When oxygen is being used the air provided by the blower 6 flows solely to the interior of the hood to provide the positive pressure. If, under these conditions, the blower fails, this merely means that no positive pressure is provided and the wearer merely inhales oxygen in the normal way. Failure of the oxygen supply leads to the difficult breathing conditions previously described and indicates to the wearer that the emergency supply must be connected. Finally, failure of the oxygen regulator can be remedied by operation of the valve shown in FIG. 4 as just described.

Claims

I claim:

1. A respirator comprising a hood which is dimensioned to completely cover the head of the wearer and has a terminal lower edge dimensioned to encircle the body of the wearer beneath his head to define a narrow passageway between said edge and said body,

an oro-nasal mask within said hood,

an inlet for admitting air to said hood, said inlet having two branches, one leading into said mask through a first non-return valve, and the other leading into the interior of said hood outside said mask through a second non-return valve,

a mechanical blower connected to supply air to said inlet, whereby a portion thereof passes through said second non-return valve into said hood outside said mask and thence outwardly through the passage bwtewwn the edge of the hood and the body of the wearer,

a connector for connecting said mask to a supply of oxygen, and means for preventing the flow of air from said blower to said mask while said oxygen is being supplied.

2. A respirator as claimed in claim 1 in which said first non-return valve comprises a valve-member and a seat and said flow-preventing means comprises means urging said valve member against said seat with a force small enough to permit air to flow through said first non-return valve from said blower to said mask when no oxygen is being supplied, a main spring for urging said valve member more strongly toward said seat, and means for bringing said main spring into action under the control of the oxygen pressure when said oxygen is being supplied so as to hold said valve member more firmly on said seat against the pressure of air form said blower.

3. A respirator as claimed in claim 1 in which said first non-return valve is a plate valve comprising first and second plates, a seat, a light spring positioned between said first and second plates to press said first plate against said seat, a cylinder containing a piston responsive to the oxygen pressure when oxygen is being supplied to move said second plate closer to said first plate, thus compressing said light spring, and a main spring between said plates which is shorter than said light spring and urged against said first plate by said second plate when said piston is subjected to said oxygen pressure.

4. A respirator as claimed in claim 3 comprising a spring-operated latch for holding said piston in the position to which it is moved by said oxygen pressure.

5. A respirator as claimed in claim 4 in which said latch is a spring-operated plunger passing through a sealed opening in said cylinder and being formed with a portion of reduced diameter which when brought into register with said opening, permits a throttled flow of oxygen from the interior of said cylinder to said mask.

6. A respirator as claimed in claim 1 comprising an air exhaust duct leading from said mask to the exterior of said hood.