Misconceptions and Fallacies

[Rick Inman]

Divers end recreational dives "cleaner" than technical dives.

Argon is warmer than air.

Argon is no warmer than air (one of these must be a fallacy).

Nitrox makes you feel better.

Nitrox doesn't make you feel better (one of these must also be fallacy).

A 7' foot hose wrapped around your neck will choke you.

 

[Charlie99]

Nitrox makes you feel better.

Nitrox doesn't make you feel better (one of these must also be fallacy).

The assumption that one or the other is a fallacy is a fallacy in itself.

My belief is that in the case of "nitrox makes you feel better" that the diver has been experiencing sub-clinical DCS and that the lower N2 content of nitrox improves how they feel.

If, OTOH, the dives were shorter, or the diver had a better ascent and stop procedure, then he would not experience sub-clinical DCS on air and wouldn't see an improvement when going to nitrox.

I used to see a difference in fatigue level with nitrox when I first started diving. After starting to do deep stops the difference disappeared.

Like a lot of decompression questions, there's no guarantee that the above interpretation is correct, but it consistent with what I know about decompression.

 

[wettek]

Misconception:
"Being overweighted automatically increases air consumption."

The fact is that if your buoyancy control is good, being overweighted has a zero or negligible impact.

Actually, I would tend to agree with this one.

Overweighted=more air in BCD to become neutral=more drag=more air consumption.

Everyone always stresses sreamlining and reducing bulk to be more efficient, and the BC is probably the biggest bit of kit we wear. Making it bigger by adding air to offset overweighting has got to increase drag, consequently increasing air consumption.

 

[roakey]

If you don't know anything about the topic, any instructor will appear near-godlike. It's not until years later when you have unlearned all the damaging techniques taught to you in OW class that you suddenly realize that your first instructor didn’t know diddly about diving.

There are a few exceptions. And by few, I mean very few. I know, I know, YOUR instructor is one of the exceptions. Right. Get back to me in a couple of years.

Roak -- A DM that, unfortuantely, was part of the problem many, many years ago.

 

[Charlie99]

Myth: If you have had an uncontrolled ascent incident, the answer is to add more weight.

This can be true if the reason you had a problem was that you were too underweighted to be able to hold your safety stop.

OTOH, a lot more common problem is that a diver is OVERWEIGHTED. To be neutral they then have to put a lot of air in the BCD. This big air bubble will expand upon ascending, and must be released from the BCD. If you don't then you can get into a runaway ascent. If this is the root cause, then adding more weight will make the situation worse, not better.

 

[Midnight Star]

Just because you caught it in the ocean, doesnt mean it's safe to eat.

 

[roakey]

Just because you caught it in the ocean, doesnt mean it's safe to eat.

One of my favorite responses to the claim "It's all natural!" is "Like Hemlock?"

Roak

 

[Midnight Star]

One of my favorite responses to the claim "It's all natural!" is "Like Hemlock?"

Roak

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Mike.

 

[Rick Inman]

The assumption that one or the other is a fallacy is a fallacy in itself.

I agree with what you said.

One thin for sure, at about 10 cents per cubic foot for O2, it sure makes my LDS feel better.

 

[roakey]

Myth: If you get too deep, you won't be able to add air to your BC faster than it is being compressed, and you won't be able to stop your descent.

The deeper you go, the SLOWER your BC is compressed per foot of descent. This makes such "runaway descents" more likely at shallow, not deep depths. But even there it won't happen due to the performance of even the worst of inflators.

The reason this myth persists is that people would rather blame the death of their friend on equipment, rather than human error (going too deep, getting narked out of their gourd and killing themselves).

Roak