High altitude breathing apparatus

[2] At extreme altitude, above 5,500 metres (18,000 ft), one can expect significant hypoxemia, hypocapnia and alkalosis, with progressive deterioration of physiological function, which exceeds acclimatisation.

At altitudes where the problem is hypoxia, breathing gas with a higher oxygen content at ambient pressure is a viable solution.

Mountaineering breathing apparatus provides oxygen at a higher concentration than available from atmospheric air in a naturally hypoxic environment.

It needs to be lightweight and to be reliable in severe cold, including not getting choked with deposited frost from the exhaled gas, which is saturated with water vapour at body temperature.

[10] An additional potential advantage of a rebreather is that the carbon dioxide scrubbing reaction is exothermic, and keeps the gas in the breathing circuit warm if sufficiently insulated, and it conserves humidity, reducing dehydration.

For aeronautical use the size of the ambient air orifice is controlled by an aneroid valve operator and is directly proportional to atmospheric pressure.

For aviation, the weight of the cylinder is usually not critical, and the choice of material may be affected by economic considerations such as purchase price and useful service life.

For mountaineering many users are prepared to pay a premium for the lowest weight that will contain enough gas for the climb, which tends to favour high pressure filament wound cylinders.

This type of adsorption system is therefore functionally a nitrogen scrubber, leaving the other atmospheric gases to pass through, with oxygen as the primary gas remaining.

[16] Gas separation across a membrane is also a pressure-driven process, where the driving force is the difference in pressure between inlet of raw material and outlet of product.

Pulse dose (also called intermittent-flow or on-demand) portable oxygen concentrators are the smallest units, which may weigh as little as 2.3 kilograms (5 lb) Their small size enables the user to waste less of the energy gained from the treatment on carrying them.

[4] Liquid oxygen (LOX) is used in some jet aircraft because it is lighter and requires less space than high pressure gas storage.

additional portable protective breathing equipment must be available for crew members for fighting fires in any compartments accessible in flight.

[25] The PBE must protect the user from smoke, carbon dioxide, and other harmful gases while on flight deck duty or fighting a fire, and must include a mask covering the eyes, nose and mouth (full facepiece) or the nose and mouth (orinasal mask) with additional eye protection.

Although there is considerable similarity in the basic conditions in which aviation and mountaineering breathing apparatus is used, there are differences sufficient to make directly transferable use of equipment generally impracticable.

One of the major considerations is that, unlike the aviator, the mountaineer cannot quickly descend to a safe altitude if the equipment fails, so it must be reliable.

[7] The Summit system used a small mask with nasal cannula and delivered oxygen in pulses, activated by the pressure drop at the start of inhalation.

An innovation is that the flow rate selector is on the supply hose where it can be reached easily and therefor is likely to be adjusted more frequently to suit current exertion, thereby making more efficient use of the oxygen.

An ambient air inlet valve prevents inhaling ambient air until the oxygen in the reservoir has been inhaled, and the exhaust valve provides enough back pressure to divert exhaled gas to the reservoir bag at the beginning of exhalation, when it contains very little carbon dioxide as it was in physiological dead space.

[30] British expeditions all used open-circuit oxygen apparatus, as advocated by pioneer climbers George Finch, Noel Odell and Peter Lloyd.

[35] Two days after Bourdillon and Evans, the second assault party of Edmund Hillary and Tenzing Norgay reached the summit with a much improved 22 lb open circuit continuous flow system.

[36] John Hunt considered that two assault parties using the experimental closed-circuit type was too risky despite users having achieved a faster climbing rate and also potentially having a greater range for a given supply (so that it might be possible to reach the summit from a camp on the South Col).

Performance was somewhat better than anticipated from 1952; the principal effect was to increase the work done in a day, and great improvement in their subjective state so having greater appreciation of the surroundings.

This was a non-rebreather mask which had a single non-return valve to prevent backflow into the reservoir bag which accumulated oxygen from a constant flow regulator, and delivered it at the start of inhalation.

As of 2013 this basic design is still used for open circuit mountaineering breathing sets[31] On 8 May 1978, Reinhold Messner and Peter Habeler made the first ascent of Mount Everest without supplemental oxygen.

Running out of bottled oxygen was noted as a factor in the 1979 deaths of Ray Genet and Hannelore Schmatz on Mount Everest.

On a single expedition in 2019, nine breathing sets failed on the same day, but the group was already descending and by sharing equipment managed to avoid fatalities.

This should be considered in the perspective of the total number of ascents using oxygen, which exceed 6500, so a failure rate of critical life support equipment of about 0.5% at first estimate.

Modes of failure reported include cylinder leaks, regulator malfunction, and operator error by inexperienced climbers.

The New York Times article suggests that lack of regulation in the industry in Nepal and poor equipment maintenance may be a cause of the problem.