Safety stop at 15'..........always

[Thalassamania]

The rate change of pressure has nothing to do with proximity to the surface. It has only to do with how quickly you move through the water column.

I think that he meant the percent rate of change.

 

[peterbj7]

The rate change of pressure has nothing to do with proximity to the surface. It has only to do with how quickly you move through the water column

I didn't say, because I thought it would be understood, that I am assuming a constant rate of ascent (same number of feet of ascent per minute whatever the depth). In that case, the rate of change of pressure gradually increases as you ascend, and becomes high as you near the surface.

On that basis, what you say is factually incorrect.

What matters from a health standpoint is rate of pressure change, not rate of ascent, and I deem it advisable to take a full minute from 15' to the surface.

Deeper down I'm quite happy to ascend more quickly - I may well ascend from 80' to 60' in just a few seconds.

 

[lazyturtle]

certed divers they are responsible for their own profiles

Oh I agree, everyone is responsible for themselves. However as the guide, I set the ground rules. For example I set a maximum depth, time, and minimum tank pressure to return to the boat. These limits are non-negotiable. If you want to be more conservative that my limits it's fine.

Personally I've never experienced what the OP is talking about, no one has ever argued about doing a safety stop with me.

 

[Gombessa]

Personally I've never experienced what the OP is talking about, no one has ever argued about doing a safety stop with me.

Maybe you've never run into crusty old divers who start every sentence with "Son" and talk your ear off about how much better diving was "in the old days"

 

[peterbj7]

no one has ever argued about doing a safety stop with me

Perhaps you've not dived with many Italian or Japanese divers. In my experience they tend to ignore briefings and do whatever they want to underwater. Of course I know exceptions in both cases, but especially in Egypt I have come across too many who don't just ignore briefings but actively resent being told what to do.

Like the two Italians who ignored a comprehensive and thorough but very friendly briefing before a dive near Ras Mohammed, where the key message was not to go too deep as there was a strong down current. The group leader risked her own life by going down to fetch them when they were at 55 metres on single tanks and quite unaware of the danger they were in, even though her own tank contained nitrox 32%.

OK, not refusing to do a safety stop, but far worse. Many divers there just go straight to the surface and chat while they're waiting for the group leader to finish her own.

 

[Thalassamania]

Maybe you've never run into crusty old divers who start every sentence with "Son" and talk your ear off about how much better diving was "in the old days"

'scuse me son. We were making deep stops and safety stops when y'all were flipper high to a daddy seahorse.

 

[Blackwood]

I didn't say, because I thought it would be understood, that I am assuming a constant rate of ascent (same number of feet of ascent per minute whatever the depth). In that case, the rate of change of pressure gradually increases as you ascend, and becomes high as you near the surface.

On that basis, what you say is factually incorrect.

Remember, for diving, we assume that water is incompressible.

If you ascend at a constant rate of 10FPM, the pressure will decrease at a constant rate of about .303ATM/min.

As Thal said, the percentage change of pressure decreases with depth, but the pressure-depth relationship is assumed to be linear (it's most often presented as 1ATA/33ft or 1BAR/10m across the entire water column).

 

[peterbj7]

True but unhelpful. I referred to the rate of change of pressure, not the amount of change of pressure, because that is what matters to you as a diver. The actual pressure matters not one jot to you (within normal limits) except insofar as it affects your gas consumption and the partial pressures of gas components you are experiencing. We have been talking about the effect on the body of changing pressure, and that becomes more significant as you near the surface.

"Percentage change" is a special case of rate of change, and is for these purposes the same thing. I wasn't referring to percentage change, but if that makes it clearer for you then that's fine.

Incidentally, what's your connection with Andy Huber? I know him from his diving down here. He hasn't set himself up as a certification agency has he? That's what your profile seems to say.

 

[Thalassamania]

Actually it is the percent rate of change that is most important. That's why M_o is the "Surfacing RATIO."

 

[lazyturtle]

Perhaps you've not dived with many Italian or Japanese divers.

I've taken lots of Italians...yea they don't listen. But they don't argue either. They just do whatever the hell comes to mind. I generally cringe and hope they die well after leaving the boat...

As far as the Japanese...I work in Hawaii so yea I take a LOT of Japanese folks diving. They don't ever argue, they nearly always do exactly what they are asked and are generally very good divers. Far better than the average American diver (sorry to say guys but that's how it is).

The old salts...they're often the worst. Every time I hear 'I've been diving since before you were born' I want to slap someone. My personal favorite is the guy who tells me he's been diving for 30 years...but hasn't been for 25 years and doesn't want to take a refresher course. Perfect.