WO2006050557A1

WO2006050557A1 - Low oxygen warning unit

Info

Publication number: WO2006050557A1
Application number: PCT/AU2005/001706
Authority: WO
Inventors: Grant Wallace Mckenzie; Alan John Miller; Alan John Lindrea
Original assignee: Csmu Technologies Pty Ltd
Priority date: 2004-11-09
Filing date: 2005-11-09
Publication date: 2006-05-18

Abstract

A low oxygen warning unit (LOWU) comprises an oxygen sensor which responds to the partial pressure of oxygen in a confined space, a processor which processes the response signal from the sensor compensating for changes in ambient pressure and temperature, and a display incorporating visual and audible alarms which are triggered when the response signal from the sensor is outside a defined safe range. The oxygen sensor is an oxygen fuel cell calibrated to measure the percentage volume of oxygen in the space, the visual alarm of the display is an ultrabright red LED warning light and the audio alarm is an electromagnetic siren.

Description

LOW OXYGEN WARNING UNIT

FIELD OF THE INVENTION

This invention relates to instruments for monitoring the level of oxygen and other gasses in confined spaces and for warning occupants when the atmosphere is unsafe for humans or animals.

BACKGROUND OF THE INVENTION

In the history of pressurised aircraft a significant number of accidents have almost certainly been caused by the crew succumbing to hypoxia commonly known as oxygen starvation. However because of the nature of hypoxia, this cause of accidents usually cannot be confirmed beyond all doubt.

Hypoxic hypoxia is the most common form of hypoxia encountered in aviation and occurs at the lung level and is commonly called altitude hypoxia. Pilots may experience hypoxic hypoxia when flying at altitude in an unpressurised aircraft, since with increasing altitude, the molecules of oxygen in ambient air get farther apart and exert less pressure.

The percentage of oxygen does not change as the aircraft climbs but the partial pressure of oxygen in the ambient air decreases. In other words, with increasing altitude, the partial pressure of oxygen gets lower and the lungs cannot effectively transfer oxygen from the ambient air to the blood to be carried to all tissues in the body.

A second type, hypemic hypoxia, is caused by the reduced ability of the blood to carry oxygen. For a pilot, this means that, even though there is an adequate supply of oxygen to breathe, the blood's capacity to carry the oxygen to the cells has been impaired. There are a number of causes for this including anaemia, haemorrhage, haemoglobin abnormalities, sulpha drugs, nitrites, and carbon monoxide since these interfere with the ability of the blood to carry oxygen and reduce the amount of oxygen the blood can carry to the celts. The most common cause of hypemic hypoxia in aviation occurs when carbon monoxide is inhaled as a result of aircraft heater malfunction, engine manifold leaks, or cockpit contamination with exhaust from other aircraft. Haemoglobin bonds with carbon monoxide two hundred times more readily than it bonds with oxygen and carries the former rather than the latter to cells which are thereby starved of oxygen.

A third type, stagnant hypoxia, occurs when the blood flow is compromised for any reason and sufficient oxygen cannot get to body tissues. For the crew, this means that even though there is an adequate supply of oxygen to breathe, it is not getting to the cells of the body tissues to support their metabolism.

Decreased blood flow can result from the heart failing to pump effectively, arterial constriction pooling the blood as occurs during neurologic shock or from enlarged veins in the lower extremities. Stagnant hypoxia also happens when the body is exposed to cold temperatures because blood flow to the extremities decreases. This may happen following a rapid decompression during flight or while operating an aircraft in cold weather conditions without cabin heating.

The fourth type, histøxic hypoxia occurs at the cell level when the cell cannot use oxygen to support metabolism. For the crew, this means that even though there is an adequate supply of oxygen to breathe and that oxygen is being circulated by the blood, the cells are unable to accept or use the oxygen. Alcohol, narcotics, and cyanide are three primary causes of histoxic hypoxia; cyanide is a by-product of the combustion of plastics such as are used in aircraft cabins.

No matter what type of hypoxia a person is experiencing, the signs, symptoms and effects are basically the same. Hypoxia is a constant and dangerous accompaniment to flying because the human body does not have an effective warning system against the threat of loss of consciousness. Many incidents and some accidents in aviation are officially attributed to the pilot's inability to detect hypoxic conditions, with the result that the pilot's skills and judgment are impaired. In some crashes the only explanation is that the crew and passengers have lost consciousness without realising what is happening to them. There have been a number of attempts to address this serious threat to aviation safety most of which have focussed on monitoring cabin pressure. The US Federal Aviation Authority requires that supplemental oxygen be used any time the equivalent cabin pressure altitude exceeds 10,000 feet for 30 minutes or 12,000 feet for any period of time. For example GB601058 and GB711270 disclose early systems utilising barometric gauges for monitoring aircraft cabin pressure. However these systems only monitor absolute pressure and do not detect and warn of dangerous conditions due to lack of oxygen or the presence of harmful gasses such as carbon monoxide.

The US National Aeronautics and Space Administration has developed a Personal Cabin Pressure Monitor and Altitude Warning System which is disclosed in US Patent No 6,452,510. The instrument uses a calibrated, temperature compensated, pressure transducer which functions independently of other aircraft systems and detects and warns of low partial pressure of oxygen. However the disclosed preferred system is still only a sophisticated version of the early altitude warning devices above which only monitor cabin pressure altitude rather than partial pressure of oxygen and so does not warn against all dangerous environmental conditions which can cause hypoxia.

OBJECT OF THE INVENTION

Accordingly it is an object of the present invention to provide an instrument which gives adequate warning of environmental conditions which could cause hypoxia or at least which overcomes some of the deficiencies of the prior art devices.

SUMMARY OF THE INVENTION

According to the present invention a low oxygen warning unit (LOWU) comprises an oxygen sensor which responds to the partial pressure of oxygen in a confined space, a processor which processes the response signal from the sensor compensating for changes in ambient pressure and temperature, and a display incorporating visual and audible alarms which are triggered when the response signal from the sensor is outside a defined safe range. Preferably the oxygen sensor is an oxygen fuel cell calibrated to measure the percentage volume of oxygen in the space.

Preferably the visual alarm of the display is an ultrabright red LED warning light.

Preferably the audio alarm of the display is an electromagnetic siren.

Preferably the low oxygen warning unit is provided with an interface to facilitate interfacing the unit with environment control systems such as those installed in aircraft.

Preferably the ambient pressure and temperature measurements are provided by an interfacing environment control system.

In an alternative form of the invention a method of monitoring and alerting an occupant of a confined space to the danger of hypoxia comprises measuring the partial pressure of oxygen and representing it as a percentage by volume of the atmosphere in the space, compensating this percentage measurement for changes in ambient temperature and pressure and displaying the compensated percentage on a display which also incorporates visual and audible alarms which are triggered when the percentage is outside a defined safe range.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention is now described by way of example only with reference to the accompanying drawings m which:

Fig 1 shows the display panel of a low oxygen warning unit

Fig 2 is a schematic of the oxygen sensor of the unit

Fig 3 is a flow diagram illustrating the operation of the unit

Figs 4 to 7 show the display panel in four operating modes

Fig 8 is a circuit diagram showing interface options

Figs 9 and 10are tables of settings for the switches of Fig 8 and

Fig 11 shows the reverse side of the display panel of Fig 1. 6

DETAILED DESCRIPTION OF THE INVENTION

The low oxygen warning unit (LOWU) of the present invention is a cockpit mountable instrument with a readout giving the pilot a constant visual indication of the oxygen levei in the aircraft. It monitors the cabin environment in a pressurized or unpressurized aircraft and gives a visual and aural alarm if the oxygen level falls below a defined critical limit.

The calibration and measurement of the oxygen state is generated from a number of different environmental factors. In order to produce a reliable indication, three different types of sensors are employed to give a reading of oxygen by volume. The LOWU interprets readings from a cabin pressure sensor, a temperature sensor and an oxygen partial pressure sensor.

The display panel shown in Fig 1 has a six way operating switch 1, a four segment alpha/numeric readout window 2, an ultra bright red LED warning light 3, an electromagnetic audible alarm 4 and a breather hole 5 for an oxygen sensor. The six way switch 1 has the following positions - OFF / ON / CAL / RUN / DIM / AUDIO OFF. The LOWU essentially relies on an oxygen fuel cell, shown schematically in Fig 2, which generates a current proportional to the cockpit oxygen partial pressure. It compensates for variations in temperature and pressure by using ambient cabin temperature and pressure sensors to correct the fuel cell current.

The electrochemical oxygen fuel cell is a self-powered, diffusion limited, metal-air battery type comprising an enclosure 11 which contains a sensing cathode 12 which is coated with an active catalyst and an anode 13 which is a block of lead metal. This sensor uses a solid membrane 14 through which oxygen diffuses to the sensing cathode 12. Two current collectors 15 and 16 are connected to pins 17 and 18 which protrude externally and allow electronic connection to an interface board.

The entire cell is filied with conductive electrolyte 19 which allows transfer of ionic species between electrodes 12 and 13. The sensor is calibrated to measure the amount of oxygen as a percentage by volume of the atmosphere and the output signal is read as a number between zero and 100 appearing in readout window 2 of the display panel in Fig 1. The LOWU can be powered from the 5 or 28 volts DC power supply of an aircraft and has three main printed circuit boards which are shown schematically in the flow diagram of Fig 3. Display panel 21 accommodates visual 3 and audio 4 components of the unit. Two additional printed circuit board mount switches 111 and 112 are located for easy access on the reverse side of panel 21 as shown in Fig 11. These switches 111 and 112 allow for variations in display panel 21 illumination on installation.

A common interface 22 acts as a signal acceptance network to configure the interface of the unit for different aircraft types. This signal acceptance network provides different data protocols for interfacing different aircraft systems. The main task of processor 23 is to process the output signals from oxygen sensor 24. Cabin pressure and temperature sensors are also accommodated by processor 23 to compensate the output of oxygen sensor 24 for ambient changes. Processor 23 also runs calibration and built in initiation tests for interface 22 with external systems for the purpose of lighting intensity, waring/caution lighting and pressurisation.

When six way switch 1 is turned from OFF to ON as shown in Fig 4 the LOWU powers up and runs through a self test, checking the functions of display panel 21, including audio 3 and visual 4 alarms. When switch 1 is turned to CAL as shown in Fig 5 the LOWU takes a reading from the oxygen sensor and applies an error correction factor to bring it to 20.9% which is the normal safe amount of oxygen by volume in the cabin. This error correction factor will be applied to all readings until the unit is next calibrated.

When switch 1 is turned to RUN as shown in Fig 6 the LOWU monitors current from the oxygen fuel cell; if the oxygen level reading drops below 20.9 the LOWU triggers audio 3 and visual 4 alarms as shown in Fig 7 and periodically re-checks the fuel cell current. If the value returns to 20.9, then alarms 3 and 4 stop. Switch 1 can also be turned to DIM to dim display window 2 and to AUDIO OFF to mute audio alarm 3.

Accordingly the normal operating procedure is as follows: ARMING

• Turn control switch from OFF to CALIBRATE

The four segment LCD will display [ CALJl while control unit is calibrating. The calibration should complete within seconds and then display [ DONE [ . If the calibration fails to complete | ERR | is displayed.

Turn control switch from CALIBRATE to RUN

The four segment LCD will display | RUN l momentarily then | 20.9 [ oxygen concentration.

OPERATION • Run

After the Arming procedure the function switch will be set to RUN position. The

Control Unit will supply a constant visual readout | 20.91 as an oxygen concentration on the LCD display. In acceptable environmental conditions the LOWU will remain in this state for the duration of the flight. Directly exhaling onto the face of the unit should be avoided since this may cause false warning indications.

WARNINGS

• Low Oxygen Alarm State

This state will produce several visual and audible changes below 19% oxygen concentration as follows:

1) The four segment display will begin to alternately flash between and the oxygen concentration (example level only)

2) The audible alarm will sound and

3) The ultra bright red led will light.

This alarm state will remain on until either:

1) The 02 percentage returns to normal or

2) "Audio Off' is selected and the audible alarm will cease but the flashing display and the red LED will remain in the alarm state. • High Oxygen Alarm State

This state will produce several visual and audible changes above 21 % concentration as follows:

1) The four segment display will begin to alternately flash between

I HIGH I and the oxygen concentration (example level only) I 22.0 I ,

2) The audible alarm will sound and

3) The ultra bright red led will light This alarm state will remain on until either.

1) The oxygen percentage returns to normal or

2) "Audio Off' is selected and the audible alarm ceases and the flashing display and the red LED will remain in the alarm state.

• Sensor Fail | SENS | appears when either:

1) The error factor for an ageing sensor has exceeded a pre determined figure during calibration, or

2) Erroneous readings beyond limits for a predetermined length of time during normal run mode.

SHUTDOWN / CYCLE

• Shutdown

Control Unit shutdown is activated by selecting OFF on the function switch at any stage of flight.

• Cycle

Carries out SHUTDOWN followed by ARMING procedure.

Installation of the LOWU in an aircraft is facilitated by interface board 22 shown in Fig 8 which is fitted with a signal acceptance network programmed prior to installation. A series of switch settings on interface board 22 illustrated in Figs 9 and 10 allow the LOWU to interface with various aircraft types. θ

VARIATIONS

It will be realized that the foregoing has been given by way of illustrative example only and that all other modifications and variations as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of the invention as herein set forth.

Throughout the description and claims to this specification the word "comprise" and variation of that word such as "comprises " and "comprising" are not intended to exclude other additives components integers or steps.

Claims

1. A low oxygen warning unit (LOWU) comprises an oxygen sensor which responds to the partial pressure of oxygen in a confined space, a processor which processes the response signal from the sensor compensating for changes in ambient pressure and temperature, and a display incorporating visual and audible alarms which are triggered when the response signal from the sensor is outside a defined safe range.

2. The LOWU of claim 1 in which the oxygen sensor is an oxygen fuel cell calibrated to measure the percentage volume of oxygen in the space.

3. The LOWU of claim 1 in which the visual alarm of the display is an ultrabright red LED warning light.

4. The LOWU of claim 1 in which the audio alarm of the display is an electromagnetic siren.

5. The LOWU of claim 1 which is provided with an interface to facilitate interfacing the unit with environment control systems such as those installed in aircraft.

6. The LOWU of claim 5 in which the ambient pressure and temperature measurements are provided by an interfacing environment control system.

7. A method of monitoring and alerting an occupant of a confined space to the danger of hypoxia comprising measuring the partial pressure of oxygen and representing it as a percentage by volume of the atmosphere in the space, compensating this percentage measurement for changes in ambient temperature and pressure and displaying the compensated percentage on a display which also incorporates visual and audible alarms which are triggered when the percentage is outside a defined safe range.

8. The method of claim 7 in which the visual alarm of the display is an ultrabright red LED warning light.

9. The method of claim 8 in which the audio alarm of the display is an electromagnetic siren.

"10. A LOWU as herein described with reference to the accompanying drawings.

11. A method as herein described with reference to the defined operating procedure.