Let's you and I do a virtual dive to 80ft on single AL '80s, shall we? And in that dive, you have a seat failure where you start to lose your gas supply.
Dive Plan:
A critical goal in planning a dive in open water is determining how much gas is necessary for an emergency scenario, as you have listed above.
With that in mind, we want to plan for one diver to suffer an out-of-gas emergency during the deepest part of the dive, which provides sufficient reserves for any range of potential problems within the buddy group.
Let's make a few educated assumptions that leave us all with a bit of room for conservatism.
1. Let's assume that our average surface consumption rate is ~ 20 L/ 0.75 cuft per minute.
2. The assumed ascent speed will be on average 3m/10 ft per minute.
3. The average depth of the ascent is used for all calculations. Divers should attempt to maintain a controlled ascent of between 20 to 30 feet per minute and follow minimum deco (MDL/NDL) profiles. This is based on a slow but foreseeable ascent rate that provides some wiggle room for safety. Also, the 20 L/ 0.75 cuft per minute SCR is approximate based on the outcome of an average diver in most situations.
• MG should never be less than 40 bar/600psi to account for inaccuracy and/or readability in SPG's.
Let's determine our minimum gas for the dive.
Consumption= 0.75 SCR x 2 divers= 1.5 cuft /min
ATA: (80ft / 2 = 40ft); (40 ft / 33 +1 = 2.2 ATA
Time: 11 minutes (10ft/min ascent rate plus one minute at depth to resolve the problem and initiate an ascent.
1.5 x 2.2 x 11 = 36.3 cuft of gas or (36.3 / Tank Factor 2.5 x 100 = 1,452 PSI or to make it easier on the SPG 1450 or 1500 Psi to be conservitive.
• Our plan states that if we share gas from the deepest point of the dive, we require at least 1500 psi in our AL80 to reach the surface while safely transferring from one cylinder.
So,
@lexvil, at what point during the dive will we need to call it and head to the surface if all goes according to plan?