GB2201602A

GB2201602A - Closed circuit breathing/diving apparatus

Info

Publication number: GB2201602A
Application number: GB08705262A
Authority: GB
Inventors: Robin Middlemass Howie
Original assignee: Coal Industry Patents Ltd
Current assignee: Coal Industry Patents Ltd
Priority date: 1987-03-06
Filing date: 1987-03-06
Publication date: 1988-09-07
Also published as: GB8705262D0

Abstract

A closed circuit breathing apparatus has a breathing circuit comprising a breathing bag (4), personal gas supply means (5), a purifier (3) to remove carbon dioxide, a source of oxygen (1) and optionally a source of ballast gas (2). An oxygen sensor (7) provides an oxygen concentration signal to a control means (9), which compares the signal with desired values. If the desired value is not met, an actuation signal is generated to dose oxygen from cylinder (1) or nitrogen from cylinder (2) into the circuit. Another oxygen sensor 6 and/or control of the ballast gas may also be provided. If used for diving, a water pressure sensor (2, Fig. 2, not shown) may additionally provided for depth control of the breathing gas. Improved safety and economy are offered. <IMAGE>

Description

CLOSED CIRCUIT BREATHING/DIVING APPARATUS This invention concerns closed circuit breathing apparatus.

More especially it concerns such apparatus having control means for dosing oxygen into the circuit.

Closed circuit breathing apparatus of various types have been known for decades, and is used when there is a requirement for low weight or long duration. In general, the wearer of such apparatus breathes essentially pure oxygen. The wearer's exhalations are passed through a purifier or scrubber which removes carbon dioxide and a proportion of moisture, and the oxygen used by the wearer is replaced from a source which is usually compressed oxygen from a cylinder, but could alternatively be from liquified oxygen or a chemical source. In the vast majority of known apparatus, the fresh oxygen is dosed into the breathing circuit on demand; that is, the oxygen supply is actuated by a pressure-responsive valve.

In some known apparatus, oxygen is continuously supplied, and in the chemical source type, oxygen is generated according to the exhalation pattern of the wearer.

Although closed circuit breathing apparatus has many advantages over open circuit apparatus, in which the wearer's exhalations are vented from the circuit, some wearers may be physiologically unfit to breathe pure oxygen. In certain circumstances, for example in a fire situation, oxygen released from the apparatus could constitute a severe safety hazard. Pure oxygen is hazardous when used in diving apparatus and is toxic at water depths below about 13m.

The present invention provides a closed circuit breathing apparatus having a breathing circuit comprising a source of oxygen, a purifier for exhalations, a counter lung breathing bag, personal gas supply means for the wearer's inhalations and exhalations and a control means for dosing oxygen from the source into the circuit which control means comprises a gas concentration sensor capable of producing an output signal indicative of relative gas concentration, comparator means for comparing the signal from the sensor with desired values and for generating an actuation signal when the sensor signal does not meet a desired value, and valve means responsive to the actuation signal to dose gas into the circuit.The invention preferably provides an apparatus comprising a source of ballast gas and further valve means responsive to an actuation signal from the comparator means, whereby an excessive oxygen concentration can be reduced by increasing the quantity of ballast gas in the circuit. Excessive pressure may be reduced by the use of a conventional pressure relief valve at a suitable point in the circuit. An additional benefit from the present invention is that gas vented need not be of a high oxygen content, thus increasing user safety in some situations.

It may be desirable to include in the apparatus of the invention, valve means for admitting a constant controlled volume of oxygen into the breathing circuit, such a volume being sufficient to support a moderate work load. This may ensure that the oxygen concentration does not fall below a pre-determined concentration under most circumstances, with the control means thus actuating oxygen dosing only :;n circumstances of heavy physical work.

The gas concentration sensor may be a partial pressure sensor or a volume percentage sensor. A suitable electrochemical oxygen sensor is commercially available from City Technology Ltd, London.

Alternatively, thermal conductivity detectors suitable, for example, for the determination of helium or argon are available from AI Industrial, Cambridge. In most cases it may be preferred to use an oxygen sensor to indicate oxygen concentration in the circulating breathing gas, and to dose oxygen into the circuit, but in some circumstances, especially for diving, other gases may be determined and ballast gas rather than oxygen may be dosed into the circuit. Although such sensors have been found to be reliable, it is preferred to incorporate a back-up sensor connected to the comparator means.

Desirably, a controller comprises inputs from the sensor(s), the comparator means and actuation signal outputs. The actuation signal outputs may be relay operated electrical signals or may be pneumatic lines. The design of the controller may take many forms and the competent engineer should have no difficulty in reaching a satisfactory design, bearing in mind that the safety of the wearer must be considered at all time, and by conventional testing.

The apparatus of the invention may be used as a diving apparatus, in which case the control means must include an external water pressure sensor, in order to obtain a correctly compensated breathing circuit pressure. The invention does, however, also offer the possiblity of modifying the breathing gas composition according to depth, in order to maximise the safety and convenience to the wearer. It may be desirable to utilise two ballast gases, typically nitrogen and helium, in order to achieve desirable compositions. A major benefit in the use of this invention for diving apparatus is that it permits significant economies in usage of expensive ballast gases such as helium.

The wearer receives inhalation gas and exhales through a personal gas supply means which may be a mouth piece, a full face mask or helmet, or a half mask. These are conventional and may be selected by the designer of the apparatus according to its intended use. Similarly, the counter lung breathing bag may be of any convenient type including flexible bladders, inside-out bags comprising a bladder mounted in a shell, and in which the counter lung volume is defined between the shell and the outer surface of the bladder, and various types of metal breathing bags, which may comprise a movable metal diaphragm.

The source of oxygen may be conveniently one or more cylinders of compressed oxygen, eg of steel or fibre-wrapped alloy, liquid oxygen or a chemical source. The invention also extends to line breathing apparatus as well as self-contained breathing apparatus. In a line breathing apparatus, the wearer, eg a diver, is attached by an umbilical line incorporating breathing gas lines usually in addition to communication lines. The control means may therefore be remote from the wearer, providing they remain effective to control the breathing gas composition for diver's own depth.

The precise gas composition supplied from the source may be selected according to the required use and safety requirements, and may not be 100% oxygen.

The present invention is illustrated with reference to the accompanying schematic drawings, in which Fig 1 is a diagrammatic view of a self contained breathing apparatus according to the invention, and Fig 2 is diagrammatic view of a self contained diving apparatus according to the invention.

Referring to Fig 1, the breathing circuit comprises a cylinder of compressed oxygen, 1, and a cylinder of compressed ballast gas such as nitrogen, 2, connected into a pipe between a purifier 3, and a counter lung breathing bag, 4. The purifier suitably contains a charge of a carbon dioxide removing chemical such as soda lime. The purifier may also remove the moisture from the circulating gas. Between the breathing bag and the purifier is a personal gas supply means, illustrated by a mouthpiece, 5.

Adjacent to, or incorporated in the mouthpiece, are non-return valves, 6, which ensure that the gas in the circuit circulates in the correct direction. Electrochemical oxygen sensors, 7 and 8, provide output signals to a control module, 9. The control module compares the output signal from sensor 7 with predetermined desired values, and according to the oxygen concentration produces an actuation signal for a sufficient time to cause valve 10 or 11 to dose sufficient oxygen or nitrogen into the circuit to provide a desired breathing gas. Sensor 8 acts as a check on the actual gas mixture produced, and the signal from it is also fed to the control module. Sensor. 8 may also act as the main control signal generator in the case of apparent failure of sensor 7.

Referring now to Fig 2, the circuit is basically identical, and the same numbers have been used for the same items. However, a pressure sensor 12 is included, feeding a signal to the control module, which determines a rate of change of pressure and causes additional oxygen and ballast gas to be admitted through the valves 10 and 11 upon descent. The relative proportions of gas released may be controlled in a pre-determined manner which may be dependent upon depth If the control module detects an ascent, from a reduction in pressure, an actuation signal is transmitted to a vent valve, 13. The pressure sensor may, however, be replaced by a conventional pressure detector acting mechanically upon the cylinder valves to cause an increase in pressure in the breathing circuit. Similarly, the valve 13 may be replaced by a conventional mechanical excess pressure vent valve.

If desired, the control module may provide substantially pure oxygen during shallow dives or when ascending from a deep dive, for example, at depths less than lOm. This permits nitrogen in the blood to be flushed out. Optionally, for deep diving apparatus, a cylinder of helium may also be provided, the control module may then modify the breathing gas mixture to oxygen/nitrogen/helium at moderate depths and to oxygen/helium for greater depths. The oxygen and ballast gases need not be carried by the wearer.

It will be readily appreciated by the skilled man that the present invention may be modified in many respects from the details described above, without departing from the scope of the invention.

Claims

CLAIMS:

1. A closed circuit breathing apparatus having a breathing circuit comprising a source of oxygen, a purifier for exhalations, a counter lung breathing bag, personal gas supply means for the wearer's inhalations and exhalations and control means for dosing oxygen from the source into the circuit which control means comprises a gas concentration sensor capable of producing an output signal indicative of relative gas concentration, comparator means for comparing the output from the sensor with desired values and for generating an actuation signal when the sensor signal does not meet a desired value, and valve means responsive to the actuation signal to Xdose gas into the circuit.

2. An apparatus according to claim 1, comprising also a source of ballast gas.

3. An apparatus according to claim 1 or 2, wherein the gas sensor is an oxygen sensor.

4. An apparatus according to claim 1, 2 or 3, wherein the control means comprises a further gas sensor capable of producing an output signal indicative of the concentration of a further gas in the breathing circuit, and the comparator means is capable of generating a further actuation signal when the further gas sensor signal does not meet a desired value.

5. An apparatus according to any one of the preceding claims, wherein valve means is provided for admitting a constant controlled volume of oxygen into the breathing circuit.

6 An apparatus according to any one of the preceding claims and in the form of a diving apparatus, comprising also a water pressure sensor effective to control the pressure of gas in the breathing circuit.

7. An apparatus according to claim 6, wherein the control means provides different pre-determined breathing gas compositions according to the depth as detected by the water pressure sensor.

8. An apparatus according to claim 7, comprising sources of oxygen and two ballast gases and the control means controls dosage of each gas into the breathing circuit.

9. An apparatus according to any one of the preceding claims comprising main and back-up gas sensors.

10. An apparatus according to claim 1, substantially as hereinafter described.