GB2215216A

GB2215216A - Positive pressure breathing apparatus

Info

Publication number: GB2215216A
Application number: GB8804813A
Authority: GB
Inventors: Keith Simpson
Original assignee: Sabre Safety Ltd
Current assignee: Sabre Safety Ltd
Priority date: 1988-03-01
Filing date: 1988-03-01
Publication date: 1989-09-20
Anticipated expiration: 2008-03-01
Also published as: GB2215216B; GB8804813D0

Abstract

A warning of a fall in the gas pressure within a positive pressure breathing apparatus, which comprises a face mask 1 having a filter canister 4 mounted to an air inlet 3 within which there is located a fan 5 for drawing air through the filter canister 4, is provided by a solid state infra-red proximity detector 9 located adjacent to a pressure sensing diaphragm 8. The diaphragm 8 is acted upon on one side by the pressure within the face mask 1 and on the other side by the ambient atmospheric pressure. When the pressure within the face mask 1 approaches ambient pressure and becomes negative the diaphragm 8 moves towards the proximity detector 9 which senses the movement of the diaphragm 8 and gives an output which is caused to illuminate a light emitting diode 11 positioned with the face mask 1 in an area visible to the eye of the wearer and also visible to a supervising officer working with the wearer of the positive pressure filter respirator. <IMAGE>

Description

POSITIVE PRESSURE BREATHING APPARATUS This invention relates to positive pressure breathing apparatus.

In positive pressure breathing apparatus a positive pressure greater than the ambient pressure is maintained within a protective device such as a face mask or a hood surrounding the respiratory passages of a wearer. The use of positive pressure has the particular advantage that, if there is any leakage, the leakage will all be outward from the protective device thus providing a high degree of protection against the ingress of noxious fumes into the gas which the wearer of the apparatus is breathing.

Positive pressure filter respirators are one form of positive pressure breathing apparatus in which the positive pressure is provided by means of an air mover such as a blower or a fan which delivers air through a filter to the interior of a face mask, helmet or hood. The air mover, which may be a battery-driven electrical device, removes from the wearer the need to overcome the resistance of the filter and so reduces the breathing effort required.

In positive pressure filter respirators of this type the positive pressure may fall to a negative pressure inside the mask, helmet or hood due to: a) Failure of the battery - for example, running flat.

b) Failure of the filter - for example, becoming clogged.

c) Failure of the fan - for example, failure of the bearing.

d) Excessive leakage - for example, due to poor mask fit or poor fitting of the mask by the wearer.

Other forms of positive pressure breathing apparatus are, for example, self-contained compressed air open circuit breathing apparatus and self-contained compressed oxygen closed circuit breathing apparatus.

In all positive pressure breathing apparatus the positive pressure may fall to a negative pressure due to some failure in the apparatus which is not immediately evident to the wearer.

According to the present invention there is provided positive pressure breathing apparatus comprising protective means for surrounding the respiratory passages of a wearer thereof to exclude noxious atmospheric gases from the space within the protective means and adjacent to the said respiratory passages, means for supplying breathable gas to the protective means at a rate faster than the rate of leakage of gas from the protective means, and means within the protective means and responsive to a fall in the gas pressure within the protective means below a predetermined level for providing a signal when the gas pressure within the protective means falls below the said predetermined level.

The protective means may comprise a hood, a helmet or a face mask.

More specifically in accordance with the present invention there is provided a positive pressure filter respirator comprising a face mask having sealing means for engaging the face of the wearer to surround his respiratory passages to exclude noxious atmospheric gases from the space within the protective means and adjacent to the said respiratory passages, an air inlet to the face mask, a filter mounted in the air inlet, air moving means for moving air through the filter into the face mask to maintain a pressure above ambient pressure within the face mask, detector means located within the face mask for detecting a decrease in the gas pressure within the face mask, and indicator means operable by the detector means for providing a signal when the pressure within the face mask falls below a predetermined level.

Preferably the detector means comprises a diaphragm mounted in the proximity of an infra-red detector which gives an output dependent on the position adopted by the diaphragm under the gas pressure within the face mask.

Advantageously the indicator means comprises means for giving a visual indication when the output from the infra-red detector indicates that the pressure within the face mask has fallen below the predetermined level.

Conveniently the indicator means provides a signal when the gas pressure within the face mask falls below ambient pressure. The positive pressure filter respirator according to the present invention thus provides a negative pressure alarm which detects when a positive pressure ceases to exist close to the nose or mouth of the user.

The present invention will be further understood from the following detailed description of a preferred embodiment thereof which is made, by way of example, with reference to the accompanying drawings, in which, Figure 1 is a cross-sectional side view of a positive pressure filter respirator incorporating the present invention, Figure 2 is a diagrammatic representation of an electrical circuit for use in the embodiment of the invention illustrated in Figure 1, and Figure 3 is a graphic representation showing three curves showing pressure in a positive pressure filter respirator in relation to ambient pressure during the breathing cycle.

Referring to Figure 1 there is shown a positive pressure filter respirator which includes a full face mask 1, having a visor 2 and an air inlet generally designated 3 to which a filter canister 4 is screwmounted. Immediately within the filter canister 4 there is located a fan 5 which is arranged to be driven by a battery-operated motor 6 so as to draw air through the filter canister 4 and into the interior of the full face mask 1. A curved wall portion 7 within the mask 1 directs the air drawn through the filter canister 4 by the fan 5 across the visor 2.

In operation the fan 5 draws air through the filter canister 4 at a rate greater than the rate of leakage of gas from the full face mask 1 so that a positive pressure above the pressure of the ambient atmosphere is maintained within the mask 1.

In accordance with the present invention a negative pressure alarm is provided within the full face mask 1 at a position where it can detect the pressure within the mask 1 without being affected by any force arising from gas flow within the mask 1. The negative pressure alarm comprises a pressure sensing diaphragm 8 and a solid state infra-red proximity detector 9. The upper side of the diaphragm 8 responds to the pressure within the full face mask 1 and the lower side of the diaphragm 8 is subject to the ambient atmosphere as a result of the presence of an aperture 10 in a portion of the full face mask 1 behind the position at which the diaphragm 8 is mounted.

In normal operation the positive pressure within the full face mask 1 holds the diaphragm 8 away from the proximity detector 9 as shown in- Figure 1. However, when the positive pressure falls, the diaphragm 8 moves towards the proximity detector 9 and is sensed by the proximity detector 9 as the pressure approaches the ambient pressure and becomes negative, i.e. falls below the ambient pressure. A small light emitting diode (LED) 11 positioned within the full face mask 1 in an area visible to the eye of the wearer but not interfering with his normal vision is illuminated when the pressure within the face mask becomes negative.

Advantageously the light emitting diode 11 is so positioned within the full face mask 1 that its light can also be seen externally by a supervising officer working with the wearer of the positive pressure filter respirator according to the present invention.

In Figure 2 there is shown an electrical circuit incorporated in the positive pressure filter respirator of Figure 1. The solid state infra-red proximity detector 9 comprises the diode 13 and the infra-red responsive transistor 14, the voltage across the transistor 14 increasing as the infra-red radiation received by the transistor increases in consequence of the approach of the diaphragm 8 to the transistor 14.

A proportion of the voltage developed across the transistor 14 is selected by the adjuster 15 and compared with a standard voltage by a voltage comparator 16. The proportion of the voltage across the transistor 14 selected is advantageously chosen such that the voltage comparator 16 gives an output causing the LED 11 to be illuminated when the pressure within the full face mask 1 goes negative.

In Figure 3 there are shown diagrammatical representations of the pressure within the full face mask 1 during the breathing cycle. The curve at (a) in Figure 3 represents the pressure within the full face mask 1 when the positive pressure filter respirator is working normally and the pressure within the mask 1 does not fall as low as the ambient pressure at any time in the breathing cycle.

The curve at (b) in Figure 3 shows that, when the pressure within the full face mask 1 has fallen sufficiently for the pressure in the mask 1 to fall below ambient during the inhale portion of the breathing cycle, the LED 11 will be illuminated for the periods indicated by shading 17. Thus the initial onset of a momentary failure of positive pressure will produce a small flash of illumination during the brief time that the pressure is negative. As this brief time lengthens, the duration of the flash will increase until, finally, complete failure of positive pressure results in illumination during the entire period of the inhale cycle, as shown at (c) in Figure 3.

The positive pressure filter respirator also provides an advantage in connection with the donning procedure for breathing apparatus when it is essential that there is a good fit of the face mask 1 to the wearer. During normal donning of a full face mask, the air inlet is turned off and either a negative or positive pressure is induced in the face mask cavity by use of the lungs. The breath is held and the degree of the fit of the face mask is assessed subjectively by the length of time before the induced pressure disappears.

When donning the full face mask 1 of a positive pressure respirator in accordance with the present invention, it is possible to time more accurately the period until the pressure disappears and this gives a better assessment of the adequacy of the mask fit by assessing the rate of decay of the induced pressure with the addition of simple logic circuitry.

Claims

CLAIMS:

1. Positive pressure breathing apparatus comprising protective means for surrounding the respiratory passages of a wearer thereof to exclude noxious atmospheric gases from the space within the protective means and adjacent to the said respiratory passages, means for supplying breathable gas to the protective means at a rate faster than the rate of leakage of gas from the protective means, and means within the protective means and responsive to a fall in the gas pressure within the protective means below a predetermined level for providing a signal when the gas pressure within the protective means falls below the said predetermined level.

2. Positive pressure breathing apparatus according to Claim 1 wherein the protective means comprises a hood.

3. Positive pressure breathing apparatus according to Claim 1 wherein the protective means comprises a face mask.

4. Positive pressure breathing apparatus according to any one of Claims 1 to 3 wherein the said means for supplying breathable gas to the protective means comprises a filter and air moving means for moving air through the filter into the protective means.

5. A positive pressure filter respirator comprising a face mask having sealing means for engaging the face of the wearer to surround his respiratory passages to exclude noxious atmospheric gases from the space within the protective means and adjacent to the said respiratory passages, an air inlet to the face mask, a filter mounted in the air inlet, air moving means for moving air through the filter into the face mask to maintain a pressure above ambient pressure within the face mask, detector means located within the face mask for detecting a decrease in the gas pressure within the face mask, and indicator means operable by the detector means for providing a signal when the pressure within the face mask falls below a predetermined level.

6. A positive pressure filter respirator according to Claim 5 wherein the detector means comprises a diaphragm mounted in the proximity of an infra-red detector which gives an output dependent on the position adopted by the diaphragm under the gas pressure within the face mask.

7. A positive pressure filter respirator according to Claim 6 wherein the indicator means comprises means for giving a visual indication when the output from the infra-red detector indicates that the pressure within the face mask has fallen below the predetermined level.

8. A positive pressure filter respirator substantially as hereinbefore described with reference to the accompanying drawings.

8. A positive pressure filter respirator according to any one of Claims 5 to 7 wherein a signal is provided by the indicator means when the pressure within the face mask falls below ambient pressure.

9. A positive pressure filter respirator substantially as hereinbefore described with reference to the accompanying drawings.

Amendments to the claims have been filed as follows CLAIMS: 1. Positive pressure breathing apparatus comprising protective means for surrounding the respiratory passages of a wearer thereof to exclude noxious atmospheric gases from the space within the protective means and adjacent to the said respiratory passages, means for supplying breathable gas to the protective means at a rate faster than the rate of leakage of gas from the protective means, and detector means which comprises a diaphragm mounted in the proximity of an infra-red detector located within the protective means and which is responsive to a fall in the gas pressure within the protective means below a predetermined level for providing a signal when the gas pressure within the protective means falls below the said predetermined level.

5. A positive pressure filter respirator comprising a face mask having sealing means for engaging the face of the wearer to surround his respiratory passages to exclude noxious atmospheric gases from the space within the protective means and adjacent to the said respiratory passages, an air inlet to the face mask, a filter mounted in the air inlet, air moving means for moving air through the filter into the face mask to maintain a pressure above ambient pressure within the face mask, detector means located within the face mask for detecting a decrease in the gas pressure within the face mask, the detector means comprising an infra-red detector and a diaphragm mounted in the proximity of the infra-red detector which gives an output dependent on the position adopted by the diaphragm under the gas pressure within the face mask and indicator means operable by the detector means for providing a signal when the pressure within the face mask falls below a predetermined level.

6. A positive pressure filter respirator according to Claim 5 wherein the indicator means comprises means for giving a visual indication when the output from the infra-red detector indicates that the pressure within the face mask has fallen below the predetermined level.

7. A positive pressure filter respirator according to either Claim 5 or Claim 6 wherein a signal is provided by the indicator means when the pressure within the face mask falls below ambient pressure.