Surface pressure

[CuzzA]

no seatbelt law in my state.....i still wear one.....

neither did seatbelts.

It's coming in your state.

And the law is based on data showing not wearing a seat belt will likely lead to death and injury in a car accident.

Not doing a safety stop will not likely lead to being bent. It's a very poor analogy.

But it's a good practice to teach for the masses where age, fitness and skills are not considered. In other words, it relieves the training agencies of having to consider those three things. 60 years old, out of shape and poor buoyancy control? Not to worry, as long as you do your safety stop it's extremely unlikely you'll get bent.

 

[John C. Ratliff]

Every dive op that I've heard talk about this issue during the dive briefing has specified back on the boat, not starting a safety stop, with no less than 500 psi. Most of them also talk about arriving at the safety stop with 1000 psi.

The reason for the dive operators is that these are rental systems, and if you take a rental system to zero psi, you have the chance of water inside the tank. This means a visual inspection is required in order to put the tank back into service. If you see water inside the tank, the rental regulator needs an overhaul too, so you cannot put them back immediately into service. Hence, come back with 500 psi in your tank. We (the dive operator) then knows there is no possibility that the regulator or tank has been compromised with seawater.

SeaRat

 

[CuzzA]

The reason for the dive operators is that these are rental systems, and if you take a rental system to zero psi, you have the chance of water inside the tank. This means a visual inspection is required in order to put the tank back into service. If you see water inside the tank, the rental regulator needs an overhaul too, so you cannot put them back immediately into service. Hence, come back with 500 psi in your tank. We (the dive operator) then knows there is no possibility that the regulator or tank has been compromised with seawater.

SeaRat

If I were running a business for the masses I'd ask the same of my customers for those reasons.

If not and you get back from the trip and a bunch of tanks and regs are potentially wet, well you're working all night to be back up and running the next day.

 

[M-Cameron]

It's coming in your state.

And the law is based on data showing not wearing a seat belt will likely lead to death and injury in a car accident.

depends on the severity of the accident....

Not doing a safety stop will not likely lead to being bent. It's a very poor analogy.

..and much like the accident....it depends on the details of the dive...

bodies react to decompression differently.....hell, even the same person on different days will react differently...how many dives you did that day, how much water youve drank, how much time you spent at depth, how much you exerted yourself on the dive......all going to effect how you decompress.

simply saying "yeah its not likely going to result in injury" is literally like someone saying "yeah, if i get into a crash, im not likely to get too hurt".....it depends....


there is literally 0 downside to doing a SS...especially considering we still dont have the best grasp of decompression science...and dive tables and dive computers are working on theoretical averages.....

 

[John C. Ratliff]

depends on the severity of the accident....

..and much like the accident....it depends on the details of the dive...

bodies react to decompression differently.....hell, even the same person on different days will react differently...how many dives you did that day, how much water youve drank, how much time you spent at depth, how much you exerted yourself on the dive......all going to effect how you decompress.

simply saying "yeah its not likely going to result in injury" is literally like someone saying "yeah, if i get into a crash, im not likely to get too hurt".....it depends....


there is literally 0 downside to doing a SS...especially considering we still dont have the best grasp of decompression science...and dive tables and dive computers are working on theoretical averages.....

The U.S. Navy dive tables are (or at least were) based upon tip top conditioned Navy divers, and not the average diving population nowadays. So being conservative is a good thing. However, you're very unlikely to get decompression sickness if you are well within the no-decompression dive tables and skip the safety stop.

Now, if you really want to be conservative, you can do what Larry Murphy, the Diving Officer for the Warm Mineral Springs Underwater Archaeological Project in 1975 did. He set up an oxygen system, whereby divers on decompression breathed on the 30, 20 and 10 foot stop pure oxygen, then when decompression was done, stayed in chest-deep water another 5 minutes. All dives were on air, some to around 200 feet in freshwater (this was before nitrox or trimix). But this is really, really conservative, but that was because they were dealing with a lot of different types of divers at a time when the diving physiology was not very well studied.

SeaRat

 

[broncobowsher]

Basic forum. It is a simple rule to keep the masses safe. Even with that rule I have seen my fair share surface with nothing. At least they surfaced.

I have been on boats that suggest coming back with 500 PSI, but don't require it. There requirement is you surface with something. If you don't have enough air left at the end of the dive to put a shot of air in the BC, you don't get a tank for your next dive and get to sit on the boat.

Failure to return with a reserve means you failed to plan for contingencies. Current a little different than expected, or shifts during the dive. Camera isn't working right and you spend longer than you thought you did squaring it away. The list goes on. Those stupid little things you can't really plan on, that is what the 500 PSI/50 bar is for.

Does it match tank size, no. It is designed to be the dumbist, simplist, works with any normal size tank rule of thumb. You don't have to think that a tank is a different size and this one is 37 bar instead of 50 bar. It is just a really simple number. Basic training (this is the basic forum, remember that) is simplified to a simple and easy to remember number.

Now if you want to go off on a tangent of what you really should be surfacing with, the advanced forum is down the hall.

 

[CuzzA]

depends on the severity of the accident....

Exactly. You hit a stopped vehicle at 30 mph is far different than 60 mph.

Same deal with diving. A 60 ft. dive is not the same as 120 ft. dive. On a 120 ft. dive, especially if I'm doing repetitive dives, I'll do a 5 minute stop.

I don't wear a seat belt if I'm driving down the street in my neighborhood to a friends house. I do if I'm getting on main roads.

For some reason you are arguing as if safety stops are mandatory, but they're not. No training agency states they are mandatory, rather highly recommended. Again, a blanket statement for every dive regardless of all the factors that go into a dive.

The main point here is you're not gonna die if you reach safety stop depth with 500 psi and surface with less than 500. And you're not likely to die if you don't even stop after a no stop dive ascending at 30 ft/ minute.

 

[M-Cameron]

For some reason you are arguing as if safety stops are mandatory, but they're not. No training agency states they are mandatory, rather highly recommended. Again, a blanket statement for every dive regardless of all the factors that go into a dive.

I have never once made that claim

 

[M-Cameron]

Basic forum. It is a simple rule to keep the masses safe. Even with that rule I have seen my fair share surface with nothing. At least they surfaced.

I have been on boats that suggest coming back with 500 PSI, but don't require it. There requirement is you surface with something. If you don't have enough air left at the end of the dive to put a shot of air in the BC, you don't get a tank for your next dive and get to sit on the boat.

Failure to return with a reserve means you failed to plan for contingencies. Current a little different than expected, or shifts during the dive. Camera isn't working right and you spend longer than you thought you did squaring it away. The list goes on. Those stupid little things you can't really plan on, that is what the 500 PSI/50 bar is for.

Does it match tank size, no. It is designed to be the dumbist, simplist, works with any normal size tank rule of thumb. You don't have to think that a tank is a different size and this one is 37 bar instead of 50 bar. It is just a really simple number. Basic training (this is the basic forum, remember that) is simplified to a simple and easy to remember number.

Now if you want to go off on a tangent of what you really should be surfacing with, the advanced forum is down the hall.

the thing is....calculating your gas SHOULDNT be an "advanced" discussion.....this should be diving 101

 

[johndiver999]

I think a big benefit of the safety stop, was to help ensure that the final portion of the ascent was slow. If the diver can and does stop at 15-20 feet, the chance for a limited-skilled diver to loose control of their ascent rate is greatly reduced and there are benefits from that - even if the stop itself is not that consequential.