No Drop Bottles for 30M+

[yle]

I've never seen a "drop bottle" in person. In Florida... they aren't used.

I've seen very few, but the one I remember was in Key West on the Vandenberg. Dive op hung a tank at 15 feet for anyone that needed it on the return. I guess they figured it was pretty common for their guests to underestimate their gas consumption when diving to 110 ft, hiding from strong current, on a single AL80.

 

[Gareth J]

For a lot of European divers, that have a qualification that includes decompression diving. There is certainly a blurring of the definitions.

I can't talk about other European training agencies, but I can about the BSAC.
I was originally taught by PADI, but immediately joined a BSAC club, where my PADI OW qualification was looked at as a non diving qualification (these days I would be able to dive within the restrictions of the PADI qualification).
I was immediately taught gas planning, DSMB, low vis' diving, decompression diving, drysuit, etc.
Normal recreational diving for me included decompression diving.
Almost before I completed by BSAC Sports Diver qualification, I was diving with a Pony and was practiced in using it.
I graduated to a twinset, and was regularly doing 20 - 30 minutes of stops.

When Nitrox appeared, that defined technical diving, a gas other than air. I did the IANTD advanced Nitrox course, this was when Nitrox was still banned by the BSAC. The trip before I did the course, one of the dives had included 60 minutes of decompression.

After I did the Advanced Nitrox course, we continued to dive air, but used 50% as a decompression gas (on air tables / computers) This was for a whole season. (There where very few Nitrox computers available at the time).
The 2nd season after gaining my Advanced Nitrox qualification I actually had the twinset cleaned for Nitrox as a back gas. We used Nitrox in Scapa as a Back Gas for the first time. Nitrox computers, breathing 50% Nitrox on the stops, but the computer set to the bottom gas.
For others on the boat, we where technical divers and nut cases because we used Nitrox.
Slowly, more and more people qualified on Nitrox, so I was no longer a technical diver, just the same as everyone else.
Then I did Trimix, I became a technical diver again. Now we recommend Normoxic Trimix for anyone beyond 40m, so this line has blurred again. CCR's are common, so this line has blurred again.

Newly qualified divers that we train (PADI OW equivalent), are qualified to use Nitrox within the course.

I am not cavern or cave qualified - so for me, this is technical diving. I don't do this because I am not qualified, or experienced. I do however do wreck penetration, with reels etc, I am qualified to teach this both the basic wreck diving course and the advanced wreck diving course.

Going back to the OP.
I have done dives with spare/drop tanks. Normally on the trapeze when we are / where doing long deep dives with multiple gases. The drop tank was is a rich decompression gas to accommodate a diver loosing when of the decompression gases. This was to avoid the KYAGB result of loosing one or both decompression gases.
We have dived with a second drop bottle on a line/buoy which is deployable, for a diver that misses the trapeze during an incident. It is dropped on the out of gas signal DSMB on a fixed 10m line. I haven't done this for a few years, so it is a rusty skill.

It wasn't until I did my CCR Trimix qualification that I really had to plan and do dives where the gas I was carrying was insufficient to get me to the surface if the unit failed. This was when I first started diving team bailout. I really don't like diving team bailout, you really need to know the team and trust them. Then having drop bottles preset on the boat becomes important again.
I am not currently doing this type of diving.

Bottles on the line/trapeze, or drop bottles are only there for emergencies only. Not part of the actual dive plan.
I've seen them used a few times when decompression cylinders / regulators have failed. I've fixed a few cylinder issues in the water for people. I have handed off my bailout to one diver when he lost his deco' gas, he would probably have been OK, but it was more comfortable, and I didn't really need it, I left him with his buddy and continued my ascent with my buddy.
I do practice handing off my bailout regularly, most of my buddies are OC divers these days.

 

[Blackcrusader]

For most people that could definitely not be done safely on a single tank.
Using a SAC of 15lpm (which is probably lower than what the average diver has) you would need ~2700l of gas for that dive.
You would barely get by with a 100cf tank on that dive, but there would be pretty much zero margin for error.
I'm talking about divers in general here, we all know you have the SAC of a fish because you've mentioned it in every single thread you've participated in for the past month, but making a statement that a dive plan like that is in any way safe for the large majority of divers is ignorant and reckless, mate...

Your reply does confirm that is can be done on a single tank even if you say not for most people. This does not make what I wrote incorrect. It can be done safely on a single tank. Single tank 120 with 230 bar would be more than enough for a lot of divers.

For myself I calculated using a sac rate of 12 so that would require 2132 liters so an AL100 would be fine for me. I would actually use less. As I mentioned anyone can call a dive so even before they got to deco if they were low on air they would not continue and ascend to shallower depths. I did not mention tank size I just said a single tank. If some people need twin tanks so be it. Anyone calculating a dive like that has to know their own capability and understand gas planning.
I have 3 dive buddies I dive with who could do that dive safely on an AL100 they are also good on air. I would not be planning a dive like that with someone I did not know.

A lot of women generally seem to be quite good on air.

 

[Blackcrusader]

For a lot of European divers, that have a qualification that includes decompression diving. There is certainly a blurring of the definitions.

I can't talk about other European training agencies, but I can about the BSAC. I was originally taught by PADI, but immediately joined a BSAC club, where my PADI OW qualification was looked at as a non diving qualification

Yeah same with me I got to Brunei and the padi OW was seen as useless so started again from the BSAC Sports novice course. I still have the manuals, they have so much more to cover in them even learning rope knots rescue navigation. Twas 1986 1987 so no nitrox back then. Being in a club so different than doing short courses on vacations.

 

[David Novo]

You can do dives much deeper on air and not exceed NDL and ascend to the surface as well. 40m is not the max depth on air for recreational for some agencies. I posted the 45m dive I did on air in this thread.

So you are assuming no deco and that both your buddy and you would have a SAC of 12L/min in case of an emergency, correct?

 

[Diving Dubai]

The PADI requirements, both DM and Deep Diver, are only to teach the students how to put such a bottle in place in case one is to be used. It is not otherwise required on the dives.

Unless the Deep diver course has changed since 2018, Dive 3 requires the student to complete a simulated 8 min emergency deco stop, and breath off the drop tank for at least 1 minute. So actually it is required to be used on Deep diver, but yes on DM courses the candidates are only trained to rig them.

 

[ToneNQ]

Yeah I’m aware that you shouldn’t figure in a drop bottle for planning. My point is that in my AOW deep dives there was always one just in case...............................

When I dived at Truk, there was normally a bottle at 6m or so. The guides said nothing if you sucked on it, but your dive sites started to shallow out again. If someone in the group couldn't manage their gas the best course of action was to reduce the risk exposure.

Drop bottles are inherently risky, you have to find it first and it might have been half sucked down when you need it. If you might plausibly need spare gas at 35m, carry it. Also people panicking are not reliable people so they need things done for them. Whoever gets that job also should have extra gas to share. Some guides choose to carry a spare bottle on deep dives, or dive twins or sidemount for redundant gas. That requires a dive organisation reasonably above average, so while I have seen it once I'm not sure I'll see it too many more times.

 

[Blackcrusader]

So you are assuming no deco and that both your buddy and you would have a SAC of 12L/min in case of an emergency, correct?

Not everyone suddenly increases their sac rate to say double their normal rate in an emergency. Some people still remain calm and yes use more air but not significantly so. So lets assume a free flow or other sudden equipment failure. Does an experienced diver necessarily go into panic? No. Many divers have had issues on dives and had to end the dive without becoming a shooting star or going into a meltdown.

One of my buddies is around the same as I am on air he uses maybe 10 bar more on the same 60 - 75 minute dives we have done together. On the 45m dive I did not go into deco neither did my dive buddy. as he was a bit shallower

Let's assume for the 30m dive there is no issue before getting to deco which is 23 minutes. Using a sac rate of 12 which is more than my normal sac rate I would have used 1110 liters of the 2600 liters an AL100 would give me. Now for some dives I know my dive shop will fill my AL 100 to 115 - 220 bar not 200. But lets stick with 200 bar.

So to get to zero NDL we would still have 1500 liters of air left based on 12 which is higher than normal. I have not had any of my past 250 dives with a sac rate of more than 10l/min. If you were into deco by say 5 minutes you would still have 1200 liters of air left. Even if two divers needed 3 mins to ascend to the safety stop depth and had 5 minutes of deco time that is still plenty of air. For both divers less than 500 liters of air at a sac rate of 15l/min

Now if you say we had not gone into deco then to ascend to the surface with 2 divers sharing the tank from 30m 1500 liters of air is not going to be used in three minutes to get to the surface.

 

[David Novo]

Lets say a Nitrox 32% diver does a 30m dive rock bottom for 40 minutes, that can be done on a single tank safely.

Not everyone suddenly increases their sac rate to say double their normal rate in an emergency. Some people still remain calm and yes use more air but not significantly so. So lets assume a free flow or other sudden equipment failure. Does an experienced diver necessarily go into panic? No. Many divers have had issues on dives and had to end the dive without becoming a shooting star or going into a meltdown.

One of my buddies is around the same as I am on air he uses maybe 10 bar more on the same 60 - 75 minute dives we have done together. Let's assume there is no issue before getting to deco which is 23 minutes. Using a sac rate of 12 which is more than my normal sac rate I would have used 1110 liters of the 2600 liters an AL100 would give me. Now for some dives I know my dive shop will fill my AL 100 to 115 - 220 bar not 200. But lets stick with 200 bar.

So to get to zero NDL we would still have 1500 liters of air left based on 12 which is higher than normal. I have not had any of my past 250 dives with a sac rate of more than 10l/min. If you were into deco by say 5 minutes you would still have 1200 liters of air left. Even if two divers needed 3 mins to ascend to the safety stop depth and had 5 minutes of deco time that is still plenty of air. For both divers less than 500 liters of air at a sac rate of 15l/min

Now if you say we had not gone into deco then to ascend to the surface with 2 divers sharing the tank from 30m 1500 liters of air is not going to be used in three minutes to get to the surface.

The situation you described was 40 min at 30 m on Nitrox 32%. Not the ones you mentioned in your latter post.

With a SAC of 12 L/min, you would use 1920L on the bottom. That would leave 212L from the 2132L you stated.
Ascending at 9 m/min directly to the surface, with a SAC for both you are your buddy of 12 L/min that would take 200L of those 212L.

As such, it results that you did not consider:
1) Time to solve issues at depth;
2) Safety or deco stop;
3) Any increase in SAC due to stress (even if not double) - the world is not black and white: there is a wide range of reactions between business as usual and full blown panic.

 

[Sevenrider860]

I have seen just a few operators drop a cylinder at safety stop depth for deeper dives. Sometimes some extra weight is present. Arizona Dive Shop in Subic Bay, Philippines and Viking Diving in Pensacola, FL come to mind immediately. I may have seen a few others. I think when I went diving on the Spree @Wookie had a regulator on a very long hose at around 10 or 15 feet. The cylinder was on the boat.

Not to be expected, but not totally unusual if seen.