Gas Procedures: It’s Simple Logic
When diving with gases other than air, the biggest risk is breathing the wrong gas—leading to incorrect decompression planning or at worst CNS toxicity at depth, which is likely to result in death.
Recognising these dangers, the WKPP developed a simple set of procedures to ensure this never happens. GUE, founded by divers from around the world including the WKPP, adopted these same procedures and both organisations still use them today.
The risk of breathing the wrong gas at depth is real and has killed many divers, including some who were very well known and experienced. A recent tragedy being Carl Spencer’s death on the 2009 Britannic Expedition.
The first step we (WKPP & GUE) took to mitigate these risks was to standardise our gasses. This means that for any given depth range we know exactly what gas to take and that all bottles in the team will conform to that standard. As you can imagine this greatly simplfies gas planning, logistics and blending.
After thousands of decompression dives, our standard gases were based around a working PPO2 of 1.4 recreationally, 1.2 for technical diving and 1.6 for decompression (decreasing to 1.4 beyond 36m), with a maximum END of approximately 30m.
The second procedure we use is to analyse every bottle. No analysis, no dive. Preferably you should analyse on the day of the dive, to avoid accidental tank content changes and the analysis tape should contain the gas mixture to one decimal place, the date of analysis, your initials and the tank pressure.
However, standard gases and analysis only get you part way there. Another important procedure we have to prevent divers breathing the wrong gas, is to mark each and every bottle, other than back gas—every decompression bottle and every bottom stage.
There is no excuse for not permanently and properly marking bottles, no matter what gas is used. It could mean your life. Painted numbers can be erased with a swipe of PVC cleaner, and new ones painted on. Alternatively, MOD stickers (white with 75mm high black numbers) are readily available and are easily read underwater. Nothing else should be on the tank to indicate contents—just the MOD and the dated analysis. Any other markers merely confuse the message and introduce ambiguity where non need exist. What does a green nitrox or custom mix sticker actually tell you? Nothing of value. You must of course follow local laws regarding bottle markings, where they exist, baring in mind that the goal is clearly marked tanks with no ambiguity as to their contents and MOD. Clean, uncluttered tanks, marked correctly say a lot about the diver and their attention to these important details.
MOD markings (75mm numbers on a white background) should appear horizontally on either side of the bottle, oriented so the diver and team can read them underwater. It’s that simple.
As a 6 can look like a 9, 6m oxygen bottles are marked OXYGEN 6 to avoid any confusion. The diver’s name can also be on the bottles, clearly separated from the MOD marking. This is useful during dives where bottles are left at a decompression station or clipped to a cave line.
When correctly marked, it makes no difference where bottles are located on the diver, though to maintain a clear and freely donatable long hose, GUE divers always carry their bottles on the left. No attempt need be made to identify a gas by which side it’s on or its regulator colour—these practices can be error prone—we need only identify the bottle by its marking. The diver and team can clearly see the MOD and verify that everyone is switching to or breathing the correct gas.
Bottles are always turned off and the regulator stowed on the bottle when not in use. Stowing regulators aids team identification of breathing gas when all bottles are carried, however in cave, we never carry a bottle past its MOD. The risks introduced by trying to push a gas past its maximum operating depth, particularly in a cave or overhead environment, are simply not worth it.
If you can not see the bottle or can not identify the gas, do not breathe it—stick with a known breathing gas until you can make a positive identification. Missing a little decompression gas is far less risk than toxing.
When finished with a gas, stow the regulator back along the bottle and turn it off. It’s common to see divers surfacing with two or more decompression gas regulators around the back of their neck. This creates unneccessary clutter and in an emergency complicates gas donation, impeding the donation of both the breathing gas and potentially the long hose.
Clearly, proper procedures around gas choice, analysis, marking and switching are paramount for safe diving. There is no need for elaborate, overly complex and error prone systems, only simple, streamlined systems like that summarised here. You either follow the procedure and know what you’re breathing or you don’t.
It’s simple logic.