When planning deep dives, wreck penetrations, as every responsible diver knows, there should always be a reason; the old adage of “plan your dive, dive your plan” springs to mind.
Emergency planning is a key part of diving; everyone on their Open Water learns the Alternate Air Source or good old CESAAAAA, but what happens when you are too deep for a CESA? Your buddy better be on hand to help you, but even then will you have enough gas to make it out safely? Let’s look at an example to highlight just how much air might be needed for you and your buddy to make a safe ascent:
First of all we need to make some assumptions. The first one is that with all the “panic” of your buddy’s gas loss (total failure) then you both will be breathing a lot faster, so we are going to say 30L/min. Then it will take you both a couple of minutes to get sorted before you make your ascent. Now let’s look at the maths:
- Out of Air!=
Two of you breathing from a single tank at 30L/per min at 40m:
= 5 (depth in bar) x 30 (L/min) x 2 (people) x 2 (minutes) = 600L
Ascending up to 5 m from 40 m at 12m/min breathing from a single tank
= 2.8 (avg. depth in bar) x 30 (L/Min)x 2 (people) x 3 (minutes) = 504L
- Safety Stop (Three Minutes at Five Metres)
= 1.5 (depth in bar) x 30 (L/min) x 2 (people) x 4 (minutes including ascent) = 270L
= 600L + 504L + 270L = 1,374L
= 124 bar (11L tank)
This means that to be on the safe side, you should be ascending up from 40m with at least 124 bar in your tank in case of emergency in order for both divers to make it out safely.
This is just one of many Gas Planning calculations that can be done in order to carry out a safe dive. Whilst alot of this is only covered in ‘Technical’ diving, the same principles still apply in any sort of diving.
So come and do a PADI Deep Specialty with me, and start learning more about the Underwater World!