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I'm looking to get a bit of info on Chemical Oxygen generation, especially as done on aircraft. I understand the process of Chemical Oxygen Generation. I'm also aware that weight for weight it produces far more oxygen than Oxygen gas canisters.

What I want to know is are there any other advantages? Does it have added safety benefits when compared to high pressure gaseous oxygen storage? The Oxygen candle burns extremely hot when it goes off but I'd imagine high pressure gas canisters could be far more dangerous and prone to exploding if damaged?

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  • $\begingroup$ Are you trying to ask why oxygen generated in case of emergency in an airplane is chemical instead of using oxygen bottles? I do not see the link with aviation $\endgroup$ – Trebia Project. Apr 16 '15 at 21:05
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    $\begingroup$ I'm voting to close this question as off-topic because this question needs migration to engineering.SE... $\endgroup$ – UnrecognizedFallingObject Apr 16 '15 at 22:09
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    $\begingroup$ Apologies if I've placed it in the wrong place, yes I was aiming for the emergency oxygen generation aboard aircraft in the case of depressurisation and why airlines prefer to use the chemical version rather than canisters $\endgroup$ – Leavenotrace Apr 16 '15 at 23:30
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    $\begingroup$ I'm no expert on this one, but airlines don't really need a reason besides "weight for weight it produces far more oxygen than Oxygen gas canisters." Nobody wants to waste money flying a heavier thing around the world when a lighter version is available. $\endgroup$ – Zach Lipton Apr 16 '15 at 23:50
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    $\begingroup$ Very legitimate aviation question. Commercial aircraft have both pressurized gaseous oxygen cylinders and chemical oxygen generators. We already have a pile of O2-related questions in the sidebar, $\endgroup$ – paul Apr 17 '15 at 6:25
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Pressurized oxygen tanks have two big minus points: they are heavy, and they are essentially a small bomb. But they have two big plus points: they can be refilled easily and they don't generate any heat when you use them.

Chemical oxygen generator plus points are they are lightweight, self-contained and more-or-less maintenance-free (they don't leak). Minus points are they are single-use, time-limited and cannot be shut off.

As nearly everything in aviation is a balance of good and bad, we often see both systems being used at the same time. The flight crew will use oxygen on a regular basis - sometimes procedurally, sometimes just to clear up a headache. They need to be able to turn it on and off, and the airline doesn't want to replace the system each time.

Passengers rarely need oxygen, and when they do it's only until the plane descends to breathable altitudes (which will happen really quickly).

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An oxygen bottle is extremely heavy. And when you are on fire you don't want to have oxygen around. And in general when you have to use oxygen in an aircraft, something went wrong. A big jet is about 40 meters long which means you have at least 40 meters of oxygen pipe. By requirement oxygen should be provided from maximum altitude to around FL100 which means 20 or 30 minutes. 435 passengers needing 30 minutes of oxygen means 1 ton of deadload. Replenishing an oxygen bottle is a pain for maintenance (tank temperature, pressure, ...). Maintenance and weight are key factors in the decision.

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    $\begingroup$ This seems to suggest that bottles have no benefits and aren't used. Also, your math on that 1 ton is not really clear. $\endgroup$ – fooot♦ Apr 29 '15 at 23:42
  • $\begingroup$ When an aircraft is on fire you probably don't want to have the chemicals used in the oxygen generator around either. $\endgroup$ – rclocher3 Jun 25 at 14:49
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The disadvantages of stored oxygen are that the cylinder can be very heavy, and it contains pure oxygen which can explode on contact with fire or a source of high temperature. However, it can last longer the flow is by demand when the person inhales. This means it can last longer than the chemical generator oxygen supply.

The chemical generator is cheap, doesn't need frequent maintenance and checks, and can supply oxygen for a larger number of people without adding weight to the aircraft because the oxygen is a byproduct of the burning of Sodium Chlorate. The cons are it is one time use and can only supply oxygen for about 15-20 minutes. This means the pilot will only have enough time to descend to a lower altitude. Another disadvantage that it is a continuous supply device, whereby it will continue to supply the oxygen even when you don't need it. Once it is activated it won't stop until all the Sodium Chlorate is used up to produce oxygen.

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  • $\begingroup$ Oxygen doesn't explode by itself, even on contact with fire. It makes explosion possible when fuel (another gas or dust) is present. If you mean the cylinder which can explode when overheated, it can, but this (almost) doesn't depend on the gas inside. $\endgroup$ – Zeus Jun 26 at 1:40

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