Why Surface with 500 PSI?

[DiveClimbRide]

I would like to point out to the metric folks that 500psi is a measly 34 bar and 50bar if 725psi.

Seeing the vast difference in those pressures one could almost be tempted to think whomever made up this arbitrary rule just took the lowest number on their gauges and hey presto! The 500psi/50 bar on the boat rule is born...

 

[Centrals]

The smallest number in all my metric spg is 50 bar.

 

[NothingClever]

The smallest number in all my metric spg is 50 bar.

Seriously? I’ve never seen a metric SPG without 10 bar increments below the thicker 50 bar line. That seems simply dodgy.

 

[NothingClever]

I think the 500 psi / 50 bar rule is perfectly appropriate for all the divers out there who don’t have the aptitude or interest to learn the science of diving. I think the number of us that appreciate @rsingler RBP calculator are in the minority, TBH. I’m not trying to take our foot off the gas from learning and discussing the RBP calculator, just thinking about what I see on dive boats in Florida and the Red Sea. Come to think of it, I’m not sure many DMs that sternly warn divers to surface with min pressure could even calculate their own RBP on a personal (non-DM) dive.

If a DM / guide tells me I have to get on the boat with a minimum volume, I really don’t pay attention. They’re talking to the landlocked couple who dives one or two weekends out of the year. I don’t begrudge them their efforts to try to keep the average folks safe. I would begrudge them if they can’t hold a conversation about the science of diving with a trained, proficient diver.

 

[Scraps]

I don't dive on charter boats, hardly ever. I wouldn't respond too well toward that kind of directive - for a variety of reasons. I might ask, "does it depend on what size tank I am using"? And I would expect the response to be "no, it pertains to all tanks regardless of capacity".

If I showed up "low" I might just explain to them that yes I have complied with the 500 psi rule because I still have 800 psi in my pony- "look see for yourself".

In all seriousness, if you do the calculation correctly, you will arrive with far more than 500 psi on the boat - under normal circumstances.

If there is a REAL emergency, then the 500 psi rule is explicitly disregarded and the "reserve" is to be used to facilitate a safe ascent - not keep some $8.50/hr DM happy. So in seemingly all situations, the 500 psi rule is nonsensical.

I think you know that the rule is not designed for divers like you. It’s designed for people who need such guidance. And there are a lot more of them than there are of you.

I think you also know that the $8.50/hr DM’s (actually $0/hr DM’s plus tips) didn’t make up the rule. The owner did. And the owner made up the rule because without it, inexperienced divers are more likely to sputter to the surface with no air, to endanger themselves and their rescuers, and to compromise his equipment.

We boat crews are generally perceptive enough to know which divers have their act together and which ones bear watching.

Divers, especially those with their own tanks, who find their way back to the ascent line and approach the ladder in a composed manner get treated like the competent divers they present themselves as.

It is probably a good thing you don’t dive from charter boats very often. Because if someone interrupted my safety brief to argue that it’s stupid to require people to return with 500 PSI, I’d see to it that he returned to the dock with a full 3000+ PSI in his tanks—even if I agreed with him.

 

[Dan]

Nice spreadsheets rsingler! Couple of small errors I found in the metric sheet:

- Cell H3 should be B3*D3, is now a constant value
- Cell C10 should be B6<18 in stead of B6<20
- Text in cell A10 should be "Ascent Calc #2 (18m to 5m):" but is now dependent on input depth. --> I see this error also in the imperial version. You could additionally change cell A9 to show the input max depth rather than just the text 'max depth'.

I put both metric & imperial worksheets in one file called “Rock Bottom Pressure” with 2 tabs called “Imperial” & “Metric”. Also put a footnote about the password to edit the formula is “scuba”, in case I forget it in the future.

 

[BoltSnap]

I think the 500 psi / 50 bar rule is perfectly appropriate for all the divers out there who don’t have the aptitude or interest to learn the science of diving.

How so? Can you elaborate? Why is 500psi rule so bad? Do you want less? More?

I think the number of us that appreciate @rsingler RBP calculator are in the minority, TBH.

How does RBP contradict the 500PSI rule? In my view, the 500PSI rule is an "end" result and the RBP calculations are the means to arrive with 500 PSI (or any other appropriate value) on the surface. At the end, it doesn't matter how you calculate it, you have to be on the surface with at least 500PSI, very simple.

If a DM / guide tells me I have to get on the boat with a minimum volume, I really don’t pay attention. They’re talking to the landlocked couple who dives one or two weekends out of the year. I don’t begrudge them their efforts to try to keep the average folks safe. I would begrudge them if they can’t hold a conversation about the science of diving with a trained, proficient diver.

You don't pay attention to the instructions set by the dive leader/guide/divemaster? What do you do instead?

 

[kelemvor]

.

 

[Dan]

My good friend @stepfen has just jumped in and translated things into a metric equivalent for you liter/bar folks!
Thank you to Chania, Crete!!!
Okay, team, check the new spreadsheet in Post #1 for errors.
Is the terminology right? SAC by convention instead of RMV, since you're already in liters/min and don't use "tank factor"?

Remember that if you download to your phone for use out at the dive site, most apps unlock the spreadsheet. Be careful not to inadvertently delete formulas.

Just wondering about the vastly different minimum tank psi (cell G14) for imperial unit you use is 150 psi, but for metric it shows 50 bar (725 psi). 150 psi is about 10 bar. Sounds like divers who use metric unit are way more conservative.

When I was in Galapagos, the cruise director at the end of dive briefing told everyone to be back at 500 psi or 50 bar. I told him 50 bar is not 500 psi. 1 bar equals to 14.5 psi.

 

[jadairiii]

.... I told him 50 bar is not 500 psi. 1 bar equals to 14.5 psi.

So you wanted the DM to tell the people with SPG's reading bar, be back with 34.0136 bar?