[benzofuran]

Some divers carry a few odds and ends in their buttpacks for longer duration dives, but you never factor this sort of stay into a plan, and don't want to take unnecessary equipment or kit in with you. Where there's been a lot of sump diving (submerged passages between larger air-filled chambers), there are a number of kits like these in some areas, but they're usually left by the expedition and taken back out with them.