GB2214431A

GB2214431A - Respiratory protective apparatus

Info

Publication number: GB2214431A
Application number: GB8801629A
Authority: GB
Inventors: Michael Harvey Glynn
Original assignee: Sabre Safety Ltd
Current assignee: Sabre Safety Ltd
Priority date: 1988-01-26
Filing date: 1988-01-26
Publication date: 1989-09-06
Anticipated expiration: 2008-01-26
Also published as: GB2214431B; GB8801629D0

Abstract

A fan means 14 is utilised in a closed circuit breathing apparatus to provide an anti-anoxia feature. The apparatus includes a hood 1 having a neck seal 2, a breathing bag 3, within which there is located an oxygen cylinder 13 and the fan means 14, a carbon dioxide filter 8 and a cooler 9. The fan means 14 is arranged to be driven when oxygen is flowing from the oxygen cylinder 13 into the breathing bag 3, and the fan means 14 is positioned so as to drive gas from the breathing bag 3 through the carbon dioxide filter 8 and the cooler 9 into the hood 1. The material of the carbon dioxide filter 8 is selected to be such that gas may readily be driven through it by the fan means 14, but gas will not readily pass when the fan means 14 is not operative. Because the fan means 14 ceases to operate when the oxygen supply from the oxygen cylinder 13 fails, the wearer of the hood 1 is warned that the oxygen cylinder 13 is exhausted. A second breathing bag may be provided between the cooler 9 and the hood 1. <IMAGE>

Description

RESPIRATORY PROTECTIVE APPARATUS This invention relates to respiratory protective apparatus.

An essential integer of respiratory protective apparatus is a protective means for surrounding the respiratory passages of a wearer of the protective apparatus. The protective means may be a full face mask or a half mask which engages the face to enclose the nose and mouth only of the wearer or it may be a hood which envelopes the whole head of the wearer.

Respiratory protective apparatus incorporating a hood and a cylinder of breathable gas such as air or oxygen is already known for use in escape equipment such as for escape from a fire on board a ship or in aircraft. A hood may also be used with compressed air-line equipment, for example, in nuclear power stations or when servicing chlorine installations in swimming pools. Furthermore, hoods may be used with fresh air equipment, i.e. connected via an airline to a source of fresh air some distance from the wearer.

When a hood is used it will be fitted with a neck seal to limit the ingress of toxic gases from the surroundings and preferably the neck seal may be a diaphragm of highly elastic polymer such as silicone or polyurethane with a small central hole.

The elasticity of the material allows this hole to be expanded sufficiently to pass over the head of the wearer when donning the hood and the hole then rapidly shrinks to fit around the neck and provide an excellent seal.

It is also known to provide a hood or a full face mask with a canister containing a chemical designed to absorb or "scrub" the carbon dioxide from the exhale gas which can then be topped up with oxygen or other breathable gas from a store in the form of a small compressed gas cylinder or other source, for example a chemical which produces oxygen. The gas is then returned to the wearer for rebreathing. In such a system, it is important to minimise the volume of gas adjacent to the mouth and nose, otherwise the carbon dioxide level in the inhale gas will rise due to rebreathing of exhale gas which has not been scrubbed. This can be done by providing an inner orinasal or half mask with an inhale valve and an exhale valve.

It is an object of the present invention to provide respiratory protective apparatus in which an adequate supply of inhaled gas with a low carbon dioxide concentration is made available for the wearer in a simple manner and without the need for high rates of supply of breathable gas.

According to the present invention, there is provided respiratory protective 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, a. source of oxygen for re-charging exhaled gases with oxygen, and a fan means for causing exhaled gases to pass through a carbon dioxide filter and present filtered and re-charged gases for inhalation by the wearer.

The protective means may be a full face mask enclosing the whole of the wearer's face, including the eyes, and having first and second channels providing connections from the full face mask to a reservoir of breathable gas such as a breathing bag.

Alternatively the protective means may be a flexible hood enclosing the head of the wearer and carrying a neck seal for engaging the neck of the wearer. When a flexible hood is used, the hood itself may constitute a reservoir of breathable gas, and the source of oxygen, the fan means and the carbon dioxide filter may all be located within the hood, the fan means being so positioned in relation to the carbon dioxide filter that gas is either driven or sucked through the carbon dioxide filter to maintain a low level of carbon dioxide in the breathable gas.

In a preferred embodiment of the present invention which will be described, the protective means is a flexible hood connected by first and second channels to a separate reservoir of breathable gas in a breathing bag. The fan means and the source of oxygen, which may be a cylinder of compressed oxygen or a chemical generator of oxygen, may conveniently be located within the breathing bag. The source of oxygen may however be outside the breathing bag and oxygen from the source be fed to the breathing bag.

In all embodiments of the present invention, the use of the fan means has the effect of maintaining a good circulation of breathing gas through the carbon dioxide filter so that there is always an adequate supply of inhale gas with low carbon dioxide concentration available without the necessity of providing an inner orinasal or half mask within the protective means, whether this is a hood or a full face mask.

Advantageously, the fan means circulates gases through the carbon dioxide filter at a rate faster than the rate at which the wearer of the protective means is breathing.

Preferably, the fan means is driven in response to a flow of oxygen from an oxygen source to re-charge the exhaled gases.

In accordance with a preferred embodiment of the present invention there is provided respiratory protective apparatus comprising a flexible hood for enclosing the head of a wearer, a neck seal carried by the hood for engaging the neck of the wearer to exclude noxious atmospheric gases from the space within the hood and the neck seal, a breathing bag, first and second channels connecting the space within the hood and the neck seal to the breathing bag, one of the first and second channels including a carbon dioxide filter, a fan located in the breathing bag and operative to move gases through the carbon dioxide filter, and a source of oxygen for supplying oxygen to the interior of the breathing bag.

The carbon dioxide filter may be located in either of the first and second channels which respectively pass exhaled gases from the hood to the breathing bag and pass breathable gas back to the hood for inhalation. When the carbon dioxide filter is in the first channel, the fan is arranged to suck exhaled gases through the filter and, when the filter is in the second channel, the fan is conveniently arranged to drive gases from the breathing bag through the filter.

The second channel may include a further breathing bag, in which case the carbon dioxide filter may be located between the breathing bag and the further breathing bag. In such an arrangement the fan may be located in the second breathing bag and suck gases through the filter.

Conveniently, a cooler is located on the downstream side of the carbon dioxide filter, either adjacent to the carbon dioxide filter or spaced from it. In the latter case, for example, the filter could be located in the first channel and the cooler be located in the second channel.

Also in one embodiment of the invention which will be described the first channel includes an exhale valve, conveniently at the junction between the first channel and the interior of the hood. The second channel may include an inhale valve located between the further breathing bag and the space within the hood and the neck seal. Preferably, the further breathing bag is connected to the first channel through a pressure relief valve.

There may be further provided a turbine in a position to be driven by oxygen supplied to the breathing bag, and a motor operated by power generated by the turbine for driving the fan in the breathing bag. The source of oxygen may be located either inside or outside the breathing bag and the motor is preferably located outside the breathing bag.

Alternatively, the fan may be driven by an electric motor mounted outside the breathing bag.

Conveniently, the source of oxygen may then be located within the breathing bag.

When the fan is driven by the flow of oxygen into the breathing bag, respiratory protective apparatus according to the present invention may be arranged to ensure against anoxia in a simple manner. By choosing the material of the carbon dioxide filter such that gas does not flow readily through the filter in response only to inhalation by the wearer of the apparatus, carbon dioxide removal from the recirculated gases will cease when the fan is no longer driven by the flow of oxygen.

Broadly in accordance with this aspect, therefore, there is provided in accordance with the present invention respiratory protective 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, and gas supplying means arranged to supply breathable gas to the said space, the gas supplying means including a breathing bag, a gas source for supplying oxygen to the breathing bag, a fan located in the breathing bag and operative in consequence of a flow of oxygen into the breathing bag, a first channel connecting the breathing bag and the said space for passing exhaled gases from the space to the breathing bag through the first channel, a second channel connecting the breathing bag and the said space, and a carbon dioxide filter positioned in one of the said channels or in the breathing bag such that the fan, when operative, causes gases to be moved through the carbon dioxide filter so that filtered gases recharged with oxygen are fed for inhalation by the wearer, the carbon dioxide filter having a resistance to gas flow such that gases do not pass readily through the filter when the fan is not being driven, whereby, when the fan is no longer driven, the wearer of the protective means experiences a buildup of carbon dioxide giving warning that the rate of flow of oxygen from the oxygen source has fallen to a level insufficient to drive the fan.

As already indicated, the fan may either drive or suck gas through the carbon dioxide filter.

Although, in the preceding description, one embodiment of the present invention has been described above as having two breathing bags, these may be regarded as two parts of a single breathing bag, the parts being separated from one another by the carbon dioxide absorbent filter and optionally a cooler.

Advantageously, the two parts of the breathing bag, or the two breathing bags, however they may be regarded, are stowed inside a lower part of the hood so that they are afforded a degree of protection from hot particles in the atmosphere.

In another embodiment of the present invention which will be described, however, only one breathing bag is used.

The present invention will be further understood from the following description of preferred embodiments thereof which is made, by way of example, with reference to the accompanying diagrammatic drawings in which: Figure 1 is a side view in part cross-section of one embodiment of respiratory protective apparatus according to the present invention including a hood, Figure 2 is a side view in part cross-section of an alternative arrangement of breathing bag for the apparatus of Figure 1 in which the oxygen cylinder is positioned outside the breathing bag, Figure 3 is a side view in part cross-section of another embodiment of respiratory protective apparatus including a hood, and Figure 4 is a side view in part cross-section of a further embodiment of respiratory protective apparatus according to the invention.

In the drawings the same or similar parts are designated by like reference numerals.

Referring to Figure 1 of the accompanying drawings there is shown a flexible hood 1 made of a transparent flame resistant material such as "KAPTON" or of a commercially available flame resistant composite formed of a suitable plastics material laminated to a woven base, the composite including a visor (not shown) of a rigid transparent plastics material, for example perspex or polycarbonate.

A neck seal 2 consisting of a septum of highly elastic polymer such as silicone or polyurethane is secured to a suitable part of the interior of the hood 1, for example by welding or adhesive, for engaging the neck of the wearer to provide a good seal.

Stowed inside a lower part of the hood 1 are breathing bags 3 and 4, a first breathing bag 3 being connected to the space within the hood 1 and the neck seal 2 by a first channel 5. A non-return exhale valve 6 is provided at the junction of the first channel 5 with the neck seal 2.

The first breathing bag 3 is also connected to the space within the hood 1 and the neck seal 2 via a second channel 7 which includes the second breathing bag 4, a carbon dioxide absorbent filter or scrubber 8 and a cooler 9. The cooler 9 is provided because the chemical reaction of absorbing carbon dioxide in the filter 8 is exothermic so that the gas becomes heated. The cooler 9 may be in the form of a dispersed mass of metal such as a sintered metal block or a pad of wire wool or it may be in the form of a chemical cooler utilising the latent heat of a suitable chemical to provide cooling.

The channel 7 additionally includes an inhale valve 10 situated between the upper or second breathing bag 4 and the space within the hood 1 and neck seal 2.

The gas circuit is completed by providing a bypass 11 from the upper or second breathing bag 4 into the first channel 5 via a relief valve 12.

Mounted within the first breathing bag 3 is a compressed oxygen cylinder 13 to which a small fan 14 is fitted in such a position as to propel gas from the first breathing bag 3 through the carbon dioxide filter 8 and the cooler 9 to the interior of the second breathing bag 4. In the embodiment illustrated diagrammatically in Figure 1, the fan 14 is driven by a small pneumatic motor (not shown) the energy for which is derived by a gas turbine from the oxygen flow out of the oxygen cylinder 13.

In operation, when the hood 1 is donned, the seal to the oxygen cylinder 13 is broken and oxygen starts to flow into the first breathing bag 3. The flow of oxygen causes the fan 14 to start operating and the fan 14 drives oxygen enriched gases from the first breathing bag 3 through the carbon dioxide filter 8 and cooler 9 into the second breathing bag 4. When the wearer of the hood 1 inhales, inhale valve 10 opens and oxygen enriched gas is drawn into the interior of the hood 1 and the neck seal 2 for inhalation.

When the wearer of the hood 1 exhales, the inhale valve 10 closes and the exhale valve 6 opens permitting exhaled gases to pass into the first channel 5. The action of the fan 14 draws the exhaled gases through the channel 5 into the first breathing bag 3. The fan 14 is set such that it is moving gas from the first breathing bag 3 into the second breathing bag 4 through the carbon dioxide filter 8 and the cooler 9 at a faster rate than the wearer of the hood 1 is breathing so that exhaled gases are removed from the interior of the hood 1 and the neck seal 2 before the wearer of the hood 1 commences to inhale.Thus, when the wearer commences to inhale and inhale valve 10 opens, the wearer benefits directly from the oxygen enriched and carbon dioxide scrubbed exhaled gases which enter the interior of the hood 1 and the neck seal 2 via the inhale valve 10 and the upper part of channel 7.

Since the fan 14 is operating to direct gas through the filter 8 and cooler 9 into the second breathing bag 4, the pressure in the second breathing bag 4 may increase to an undesirable level. This is prevented by the pressure release valve 12 and bypass 11 which permit excess gas to be returned from the second breathing bag 4 to the first breathing bag 3 via the lower section of channel 5.

The system is preferably designed for an average breathing flow of 40 litres per minute with the two breathing bags 3 and 4 providing a buffer volume to cope with the variation of flow during the inhale and exhale phases of the breathing cycle.

Advantageously, the respiratory protective apparatus of the present invention is designed also to ensure against anoxia in a simple manner. This is done by selecting the material of the carbon dioxide filter 8 to be of smaller granules than the conventional filter used in respiratory systems such that gas may be readily driven through it by the fan 14 but the gas will not pass readily through the carbon dioxide filter 8 when the fan 14 is not operative.

Because the fan 14 is driven by the flow of oxygen from the oxygen cylinder 13, as long as the oxygen is flowing from the oxygen cylinder 13 the fan 14 will be driven and breathing gas will flow through the carbon dioxide filter 8 and cooler 9 maintaining an inhale gas with a low concentration of carbon dioxide. When the oxygen flow from the oxygen cylinder 13 ceases, the fan 14 will cease to rotate and gas will no longer be driven through the carbon dioxide filter 8. Consequently there will be a rapid build-up in the carbon dioxide concentration in the inhale gas so that the wearer of the hood experiences difficulty in breathing and it becomes impossible for the wearer to continue to use the hood which has to be removed long before the oxygen concentration has fallen to a dangerously low level.

If the fan 14 were to continue running when the flow of oxygen from oxygen cylinder 13 had ceased, exhaled gases would be passed through the filter 8 and carbon dioxide be removed without there being any replenishment of the gases with oxygen. The wearer would then be able to continue breathing without knowing that the oxygen concentration in the inhale gas was falling until unconsciousness set in. This possibility is eliminated by the preferred embodiment of the present invention in which the fan 14 is driven in response to the flow of oxygen from the oxygen cylinder 13 to re-charge the exhaled gases in the first breathing bag 3.

Figure 2 shows an alternative arrangement in which the oxygen cylinder 13 is positioned outside the first breathing bag 3 and, when valve 15 is opened, oxygen flows through a pipe 16 which passes through a seal in the wall of breathing bag 3 to be delivered adjacent turbine 17 to drive the fan 14.

In other alternatives which are not illustrated there could be a remote drive from an electric or hydraulic motor or turbine outside the breathing bag 3 to the fan 14.

In the embodiment of the present invention illustrated in Figure 3 inhale and exhale valves are omitted but the apparatus is otherwise similar to the apparatus of Figure 1. The fan 14 creates a continuous circulation of gas from the first breathing bag 3 through the carbon dioxide filter 8, cooler 9, the second breathing bag 4, the interior of the hood 1 and the first channel 5 back to the first breathing bag 3. This circulation of gas is at a rate faster than the rate of breathing of the wearer of the hood 1 with the result that fresh oxygen-enriched gas is available for every breath taken by the wearer of the hood 1 for as long as oxygen is supplied from the oxygen cylinder 13 to the interior of the first breathing bag 3.

Figure 4 of the accompanying drawings shows a modified version of the embodiment of the invention illustrated in Figure 3 in which the second breathing bag 4 is omitted and the second channel 7 comprises essentially the carbon dioxide absorbent filter 8, which is located outside, rather than inside, the breathing bag 3, and the cooler 9.

The cooler 9 may additionally, or alternatively, to the filter 8, be constructed so as to make passage of gas through it difficult when the fan 14 is not operative.

The preferred embodiments of the present invention which have been described provide respiratory protective apparatus incorporating a hood which encloses the head of the wearer and in which an adequate supply of inhaled gas with low carbon dioxide concentration is always available without the necessity of providing an inner half or orinasal mask within the hood. This result is achieved by maintaining a good circulation of the breathing gas through the filter of carbon dioxide absorbent material, the rate of flow of the gas through the carbon dioxide absorbent filter being faster than the rate of use of the breathing gas by the wearer of the hood.

Respiratory protective apparatus according to the present invention may be used, not only with a source of oxygen such as an oxygen cylinder positioned outside a breathing bag, but also with a remote oxygen source from which oxygen is supplied to the respiratory protective apparatus over a gas line. This remote source could be, for example, a compressed oxygen source on an aircraft.

Claims

CLAIMS:

1. Respiratory protective 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, a source of oxygen for re-charging exhaled gases with oxygen, and a fan means for causing exhaled gases to pass through a carbon dioxide filter and present filtered and recharged gases for inhalation by the wearer.

2. Respiratory protective apparatus according to Claim 1 wherein the protective means is a flexible hood enclosing the head of the wearer and the hood carries a neck seal for engaging the neck of the wearer.

3. Respiratory protective apparatus according to Claim 1 wherein the protective means is a full face mask.

4. Respiratory protective apparatus according to any one of the preceding Claims wherein the fan means circulates gases through the said carbon dioxide filter at a rate faster than the rate at which the wearer of the protective means is breathing.

5. Respiratory protective apparatus according to any one of the preceding Claims wherein the fan means is driven in response to a flow of oxygen from an oxygen source to re-charge the exhaled gases.

6. Respiratory protective apparatus comprising a flexible hood for enclosing the head of a wearer, a neck seal carried by the hood for engaging the neck of the wearer to exclude noxious atmospheric gases from the space within the hood and the neck seal, a breathing bag, first and second channels connecting the space within the hood and the neck seal to the breathing bag, one of the first and second channels including a carbon dioxide filter, a fan located in the breathing bag and operative to move gases through the carbon dioxide filter, and a source of oxygen for supplying oxygen to the interior of the breathing bag.

7. Respiratory protective apparatus according to Claim 6 wherein the second channel includes a further breathing bag, and the carbon dioxide filter is located between the breathing bag and the further breathing bag.

8. Respiratory protective apparatus according to Claim 7, wherein the second channel further includes a cooler located between the carbon dioxide filter and the further breathing bag.

9. Respiratory protective apparatus according to Claim 7 or Claim 8 wherein the second channel includes an inhale valve located between the further breathing bag and the space within the hood and the neck seal.

10. Respiratory protective apparatus according to any one of Claims 7 to 9 wherein the further breathing bag is connected to the first channel through a pressure relief valve.

11. Respiratory protective apparatus according to any one of Claims 7 to 10, wherein the first channel includes an exhale valve.

12. Respiratory protective apparatus according to Claim 6, which further includes a cooler located in the second channel between the carbon dioxide filter and the space within the hood and the neck seal.

13. Respiratory protective apparatus according to any one of Claims 6 to 12 wherein there are provided a turbine in a position to be driven by oxygen supplied to the breathing bag, and a motor operated by power generated by the turbine for driving the fan in the breathing bag.

14. Respiratory protective apparatus according to Claim 13 wherein both the source of oxygen and the motor are located outside the breathing bag.

15. Respiratory protective apparatus according to any one of Claims 6 to 12 wherein there is provided an electric motor mounted outside the breathing bag for driving the fan.

16. Respiratory protective apparatus according to any one of Claims 6 to 13 and 15 wherein the source of oxygen is located within the breathing bag.

17. Respiratory protective 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, and gas supplying means arranged to supply breathable gas to the said space, the gas supplying means including a breathing bag, a gas source for supplying oxygen to the breathing bag, a fan located in the breathing bag and operative in consequence of a flow of oxygen into the breathing bag, a first channel connecting the breathing bag and the said space for passing exhaled gases from the space to the breathing bag through the first channel, a second channel connecting the breathing bag and the said space, a carbon dioxide filter positioned in one of the said channels or in the breathing bag such that the fan, when operative, causes gases to be moved through the carbon dioxide filter so that filtered gases recharged with oxygen are fed for inhalation by the wearer, the carbon dioxide filter having a resistance to gas flow such that gases do not pass readily through the filter when the fan is not being driven, whereby, when the fan is no longer driven, the wearer of the protective means experiences a buildup of carbon dioxide giving warning that the rate of flow of oxygen from the oxygen source has fallen to a level insufficient to drive the fan.

18. Respiratory protective apparatus according to any one of Claims 1 to 17, wherein exhaled gases are caused to pass through a channel containing both a cooler and the carbon dioxide filter, and wherein the cooler is constructed to make passage of gas through the channel difficult when the fan means is inoperative.

19-. Respiratory protective apparatus constructed and arranged to operate substantially as hereinbefore described with reference to the accompanying drawings.

18. Respiratory protective apparatus according to Claim 17 wherein the protective means is a flexible hood enclosing the head of the wearer and the hood carries a neck seal for engaging the neck of the wearer.

19. Respiratory protective apparatus according to Claim 17 wherein the protective means is a full face mask.

20. Respiratory protective apparatus according to any one of Claims 17 to 19 wherein the fan circulates gases through the said first and second channels at a rate faster than the rate at which the wearer of the protective means is breathing.

21. Respiratory protective apparatus constructed and arranged to operate substantially as hereinbefore described with reference to the accompanying drawings.

Amendments to the claims have been filed as follows 1. Respiratory protective 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, a source of oxygen for re-charging exhaled gases with oxygen, a carbon dioxide filter for removing carbon dioxide from the exhaled gases, and a fan means operative in consequence of a flow of oxygen from the said source for causing exhaled gases to pass through the carbon dioxide filter and filtered and recharged gases to be presented for inhalation by the wearer, there being a resistance to gas flow through the carbon dioxide filter such that gases do not readily pass through the filter when the fan means is inoperative, whereby, when the fan means is no longer driven, the wearer of the protective means experiences a buildup of carbon dioxide giving warning that the rate of flow of oxygen from the oxygen source has fallen to a level insufficient to drive the fan means.

3. Respiratory protective apparatus according to Claim 2 which further comprises a breathing bag connected by first and second channels to the space within the hood and the neck seal, the source of oxygen being arranged to supply oxygen to the interior of the breathing bag, the fan means being located in the breathing bag, and the carbon dioxide filter being located in the second of the said channels.

4. Respiratory protective apparatus according to Claim 3 wherein the second channel includes a further breathing bag, and the carbon dioxide filter is located between the breathing bag and the further breathing bag.

5. Respiratory protective apparatus according to Claim 4, wherein the second channel further includes a cooler located between the carbon dioxide filter and the further breathing bag.

6. Respiratory protective apparatus according to Claim 4 or Claim 5 wherein the second channel includes an inhale valve located between the further breathing bag and the space within the hood and the neck seal.

7. Respiratory protective apparatus according to any one of Claims 4 to 6 wherein the further breathing bag is connected to the first channel through a pressure relief valve.

8. Respiratory protective apparatus according to any one of Claims 4 to 7, wherein the first channel includes an exhale valve.

9. Respiratory protective apparatus according to Claim 3, which further includes a cooler located in the second channel between the carbon dioxide filter and the space within the hood and the neck seal.

10. Respiratory protective apparatus according to any one of Claims 3 to 9 wherein the fan means includes a turbine in a position to be driven by oxygen supplied to the breathing bag, and a motor operated by power generated by the turbine for driving the fan in the breathing bag.

11. Respiratory protective apparatus according to Claim 10 wherein both the source of oxygen and the motor are located outside the breathing bag.

12. Respiratory protective apparatus according to any one of Claims 3 to 10 wherein the source of oxygen is located within the breathing bag.

13. Respiratory protective apparatus comprising protective means for surrounding the respiratory passages of a wearer thereof to exclude noxious atmospheric gases from the space within the preotective means and adjacent to the said respiratory passages, and gas supplying means arranged to supply breathable gas to the said space, the gas supplying means including a breathing bag, a gas source for supplying oxygen to the breathing bag, a fan located in the breathing bag and operative in consequence of a flow of oxygen into the breathing bag, a first channel connecting the breathing bag and the said space for passing exhaled gases from- the space to the breathing bag through the first channel, a second channel connecting the breathing bag and the said space, a carbon dioxide filter positioned in one of the said channels or in the breathing bag such the the fan, when operative causes gases to be moved through the carbon dioxide filter so that filtered gases recharged with oxygen are fed for inhalation by the wearer, the carbon dioxide filter having a resistance to gas flow such that gases do not pass readily through the filter when the fan is not being driven, whereby, when the fan is no longer driven, the wearer of the protective means experiences a buildup of carbon dioxide giving warning that the rate of flow of oxygen from the oxygen source has fallen to a level insufficient to drive the fan.

14. Respiratory protective apparatus according to Claim 13 wherein the protective means is a flexible hood enclosing the head of the wearer and the hood carries a neck seal for engaging the neck of the wearer.

15. Respiratory protective apparatus according to Claim 1 or Claim 13 wherein the protective means is a full face mask.

16. Respiratory protective apparatus according to any one of the preceding Claims wherein the fan circulates gases through the said carbon dioxide filter at a rate faster than the rate at which the wearer of the protective means is breathing.

17. Respiratory protective apparatus according to any one of the preceding Claims wherein the carbon dioxide filter is formed from granules of a size such that gas may be readily driven through the filter by the fan means but gas will not readily pass through the filter when the fan means is inoperative.