Decompression vs Off-gassing
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DaleC
Contributor
Or perhaps it has to do with the suffix one uses:
We are off gassing during decompression and when we leave the water but we have not yet off gassed. We also haven't decompressed or desaturated either.
The suffix ing denotes a continuing process (which in this case, no matter the verb, is correct) while ed denotes a completed process (which doesn't fully occur until sometime afterward).
Note that we have "no fly" time limits. This is the time (very liberal) that the theoretical model suggests we have decompressed to surface ambient levels, so that we can then withstand the additional pressure changes that flying will impose. We could say that we have decompressed, off gassed or desaturated at that point but again it is a semantic debate. For practical purposes, if you can get out of the water and not incur DCS symptoms, you have off gassed/decompressed/desaturated enough.
However, if you intend to fly or do a repetitive dive you need to consider yourself to be still offgassing/decompressing/desaturating, as the continued levels of N in your system will play a practical role in determining what you can do and when.
We are off gassing during decompression and when we leave the water but we have not yet off gassed. We also haven't decompressed or desaturated either.
The suffix ing denotes a continuing process (which in this case, no matter the verb, is correct) while ed denotes a completed process (which doesn't fully occur until sometime afterward).
Note that we have "no fly" time limits. This is the time (very liberal) that the theoretical model suggests we have decompressed to surface ambient levels, so that we can then withstand the additional pressure changes that flying will impose. We could say that we have decompressed, off gassed or desaturated at that point but again it is a semantic debate. For practical purposes, if you can get out of the water and not incur DCS symptoms, you have off gassed/decompressed/desaturated enough.
However, if you intend to fly or do a repetitive dive you need to consider yourself to be still offgassing/decompressing/desaturating, as the continued levels of N in your system will play a practical role in determining what you can do and when.
This technical discussion is too deep. I find myself way beyond my depth. I'm certainly not as learned as various experts, but:
It seems to me that decompression is simply the opposite of compression, and happens to every compressible object as external pressure decreases. Divers who decompress too quickly are subject to the bends, to embolisms, popping pulmonary alveoli, and other unpleasantness. Degassing is what it sounds like. In connection with scuba, degassing is a process that occurs in tissue that became saturated with gas under pressure as the external pressure is reduced during an ascent that ideally is slow enough to permit the process to be completed before bad things happen.
What's so complicated? Am I missing something? The two words have completely different meanings. In the context of scuba diving they are operationally almost identical, but they describe distinct processes.
It seems to me that decompression is simply the opposite of compression, and happens to every compressible object as external pressure decreases. Divers who decompress too quickly are subject to the bends, to embolisms, popping pulmonary alveoli, and other unpleasantness. Degassing is what it sounds like. In connection with scuba, degassing is a process that occurs in tissue that became saturated with gas under pressure as the external pressure is reduced during an ascent that ideally is slow enough to permit the process to be completed before bad things happen.
What's so complicated? Am I missing something? The two words have completely different meanings. In the context of scuba diving they are operationally almost identical, but they describe distinct processes.
DevonDiver
N/A
In your context, 'decompression diving' would be involved primarily with preventing lung-over expansion injury, rather than de-saturation (off-gassing).
As mentioned; word usage or context goes beyond the strict definition that can be attributed to that word.. and the OP inquired about the usage of a word.
The initial question was "Is there a difference". There is a difference. 'Decompression diving' has a specific meaning only as commonly understood shorthand. Lung overexpansion and inadequate desaturation both result from the process of decompression. Inadequate desaturation happens in tissue and blood. The site of lung expansion due to unreleased gas should be reasonably clear. In every case it's the gas that is compressed, not tissue. Depending on where the gas is as the time it expands a variety of things may happen, including the two mentioned consequences.
DevonDiver
N/A
In which case, you're looking at the effects of pressure... compression of gas versus saturation of gas into liquids. Agreed...they are both different effects.
However, in diving context, the word decompression is not used to deal with the volume expansion of gas on ascent - it is specifically used as a term to describe desaturation.
However, in diving context, the word decompression is not used to deal with the volume expansion of gas on ascent - it is specifically used as a term to describe desaturation.
Quite right, Devon. Not to put too fine a point on it, it's compression that causes nitrogen to convert from its gaseous state, and decompression that causes it to revert to a gas. Decompression is an entirely different concept, and not synonymous with the compound construct 'off-gassing'. That the two are frequently merged, regarded as interchangeable, by most scuba divers is neither here nor there. That sort of useage is only a simplification, a convenience. The process of off-gassing occurs during decompression. If they were synonyms the reverse might also be true. Being precise in the use of words is, I think, a good thing. Jargon is fine, as long as the user realizes that that's what it is.
DaleC
Contributor
What's confusing is when people start interchanging words they just made up.
We were talking about off gassing, not degassing (whatever that is).
I say: Lung injuries occur from over-expansion, not decompression. Because you can decompress without a lung injury but you will create an injury by over-expansion.
Now you may say: Over-expansion cannot occur without the decompression of gas.
but then I will go back to the original question and say off gassing cannot occur without decompression.
What came first, the chicken or the egg? Most people would say we were nitpicking.
Decompression theory need not be difficult for the average diver if one doesn't complicate the hell out of it.
six of one, half dozen of the other. The nitrogen doesn't care what you call it's behavior.
We were talking about off gassing, not degassing (whatever that is).
I say: Lung injuries occur from over-expansion, not decompression. Because you can decompress without a lung injury but you will create an injury by over-expansion.
Now you may say: Over-expansion cannot occur without the decompression of gas.
but then I will go back to the original question and say off gassing cannot occur without decompression.
What came first, the chicken or the egg? Most people would say we were nitpicking.
Decompression theory need not be difficult for the average diver if one doesn't complicate the hell out of it.
six of one, half dozen of the other. The nitrogen doesn't care what you call it's behavior.
dfx
Contributor
Going by simply what the words mean, decompression is the reversal of compression, and compression is the direct effect of an increase in pressure. Once you descend below the surface, you're compressing. The deeper you go, the more you compress. At the deepest point of your dive, you're compressed the most. Once you start ascending, you're decompressing. When you reach the surface, you're fully decompressed. But that doesn't mean you're fully off-gassed yet.
The potential problem is on/off gassing, which is caused by compression/decompression. (This is starting to be fun!)
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