I want to be able to produce a large amount of gas under water, from a chemical reaction, not from a pressurised cylinder (unless it is just a small cylinder that provides a chemical gas to react with something else to produce the main bulk of gas to inflate the device).
The more gas I can get from the least chemical the better. I know that any gas (even oxygen) can be toxic/dangerous in heavy concentrations, but lets just avoid the "real deadly ones".
A bit of heat from "the reaction" would be acceptable but I can't rely on HOT gases to aid inflation as when they cool and contract I will lose too much volume. It also doesn't want to be too fast/explosive as that could tend to burst the device instead of controlled deployment, even though the device would have a pressure relief valve to prevent over inflation.
So if any chemistry minded people could shine some light on a possible source of gas (30 cubic metres from a brief-case of ingredients) would be good.