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Kevin, In a message dated 97-06-15 16:20:22 EDT, you write: << For you ocean divers: 1) What is your choice of travel / deco gasses for trimix dives? I assume most people carry 2 side bottles, probably one of them is 80/20 or 100%, the other in the thirties. It looks like 80 and 32 are good choices, but I don't know, that's why I'm asking. >> I was trained using 80/20 and 36/64. There will be specific dives where other mixes will yield shorter deco times or perhaps less physiologically traumatic switches but this seems to be the "standard" right now for the average dive to around 250-300. << 2) What size do you like? I'm thinking the luxfer or catalina 40s look pretty good.>> 40 cu ft is not enough. If you run a 1/3 reserve on your deco gases you will need something on the order of 60 to 75 cu ft in many cases. Make sure the valves on deco tanks are the same (yoke or din - recommend yoke) so you can switch regulators if needed. Otherwise you will have no back up plan of any kind for deco gas regulator failure without hauling another 10 pounds of redundant regulators. Gauges on deco gases??? They add weight and failure points and you will not have to worry about losing gases if these valves are off till needed. Still, there may be times or conditions where they are wise since even though you can't often do anything about being low on a gas creative management during deco may be a factor in some cases. They also let your partner know your status at a glance if it comes into question. <<Also, do you personally travel on your thirty-ish mix to it's MOD, or just go with back gas down? >> Back gas may be hypoxic even at 16 or 17 percent O2 if "working" on the surface at either the beginning or end of the dive. Another reason for more deco mix than 40s can provide. If this is the case I will usually drop to 80 or 90 ft on 36/64 & switch over. There is no "need" to go all the way to it's MOD if the uptake of N2 or gas conservation is a concern on a slow drop or to use the deco gas at all if the PPO2 of the back gas is sufficient for the situation (assuming the dive was planned accordingly). Just make sure your PPO2 and END are good all the way down and keep the task load of switching to a minimum by not having to rush it. Keep in mind that, more than just facilitating the need to decompress, you are setting yourself up to function or survive in that top 100 or so feet of water for as long as might be necessary with little or no support. Don't treat these gases or the configuration of the equipment associated with them casually. Make sure you will be able to do anything you might have to do, including helping a buddy, and that you do not make configuration decisions that will reduce options at this stage of the dive any more than than they already are. I can not think of any important differences between the configurations suitable for cave and ocean/wreck off the top of my head. Many wreck divers stage deco gases at entry points of wrecks during penetrations. This is a judgment call based on the lesser of two evils (dragging them through a silty tangled wreck or risking not getting back to them). If you stage them and there is a collaps of wreckage behind you whatever is left of your life may be very different from that point on, be it 30 minutes or 30 years. Your choice ! Never stage deco gases on ascent lines during ocean dives ! I don't know if you are already a trimix diver or not but don't try this at home without good training. There is much more to it than the accademics and math; in fact dive planning and the management of equipment and your status both above and below the water is far more difficult to get a secure handle on than calculating mixes and stops. Plan carefully and be prepared. Chuck -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send list subscription requests to `techdiver-request@aquanaut.com'.
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