How Deep/Cold Is Safe Without Redundancy

[Nudgeroni]

There have been a number of really good posts since the Gilboa incident that point out the need for a redundant air source (ie. Pony bottle) on deep cold dives. That dive was over 100ft. with water temperatures in the low 40s.

Living in New England, I will see a range of cold temperatures and depths. Assuming I will be using good cold-water regs, at what depth do I need to have redundancy for water temps of 35, 40, 45, and 50 degrees?

BTW, I also expect to use a HP steel tank, and assume that the risk of free flow is even higher for this arrangement.

Thanks. Your info might just save my skin.

 

[fisherdvm]

Isn't Boyles Law PV= nRT

Pressure, volume, and temperature are related, right?

Then assuming that they are related in a linear fashion, by varying the temperature (in Kelvin), you will get a change in pressure. Since the volume in the first stage is constant, then you just have the pressure and temperature as variable.


Since 0 Kelvin is -273 degree Celcius, one can make a table that show the relationship of depth (affecting pressure) if temperature is held constant.

My guess is that depth is the biggest factor in freeze up. As you can shift it much quicker (from 1 atm to 4 atm from surface to depth), whereas temperature shift is smaller on the Kelvin scale.

 

[String]

Id venture that diving deep anywhere without redundancy is not safe.

Steel tank wont make any difference to freeflow risk. the difference in pressures are tiny on the scale of things.

Even good, serviced cold water regs can freeflow in cold water. Precautions such as breathing on the surface, not purging underwater etc can reduce but not eliminate the risk.

 

[SparticleBrane]

Isn't Boyles Law PV= nRT

No, that's the Ideal Gas Law.

About the OP's question, I wear doubles in the tub.

 

[drbill]

Although the waters here rarely reach lower than 50, and that generally at extreme depth, I dive with a pony on ALL dives. I used to use the "rule" that I'd wear the pony only on dives below 40 ft. However, as a videographer, I often do not dive my "plan" and found myself in potential trouble on one dive. I wear the pony on all dives whether to 10 or 200 feet.

 

[Nudgeroni]

My guess is that depth is the biggest factor in freeze up. As you can shift it much quicker (from 1 atm to 4 atm from surface to depth), whereas temperature shift is smaller on the Kelvin scale.

So temperature is *not* a factor nearly as much as depth? If that is the case, why don't they call them 'Deep Water' regs instead of 'Cold Water' regs?

 

[Blitz]

I dive cold water and I always have doubles, single and a stage or a buddy that is close enough to me to be effective. No excuse for not having some kind of redundancy

 

[IneedaName]

Isn't Boyles Law PV= nRT

.

No. That is the Ideal Gas Law and it has no relevance to adiabatic cooling and regs freezing up.

If gases were actually ideal then adiabatic cooling would not exist.

If I were crazy enough to dive water below 50 degrees I doubt I would go below 60 feet without redundancy.

 

[Nudgeroni]

String, you put me at ease a bit about the HP Steel, thanks.

Id venture that diving deep anywhere without redundancy is not safe.

Agreed, but I'm not sure what 'deep' means in 40 degree water. 40ft. is deep enough for Dr. Bill to strongly recommend a Pony. Et tu?

 

[String]

If the water is 40f it can just as much freeflow at 5ft as 150ft. Its separate to the depth issue.

However both issues combine, Deep you HAVE to have adequate redundancy whether its the tropics or the arctic. Cold water you need the right kit, precautions and then realise freeflows can still happen.
Combining the 2, deep AND cold you obviously have a higher chance of something happening AT DEPTH and having an incident.

Lets put it another way, an incident at 5ft you can just surface. An incident at 50ft you could still surface but its more complicated and riskier with more chance of things going wrong. At 100ft its even harder to get it right and more risk, 150 more again and so on. THEN add the cold water factor which increases the risk of a freeflow.

Redundancy is essential in my view.

There are no hard, fast rules. Its a personal call based on what you think your own abilities are and what amount of risk you're willing to accept. Personally i believe EVERY diver should be 100% self sufficient and not have to rely on another person for anything on any dive so i advocate redundancy for even shallow dives (as i also dont consider CESA a sane, viable or best solution to any situation)..