Abstract: Method, apparatus and breathable compositions for protecting a person from reactive oxygen species in the body are described. The invention involves providing a person with a breathing gas composition comprising at least one fuel gas compound. Apparatus and methods for providing such breathing gas compositions are described.

Abstract: A method of, and apparatus for, providing improved separation of gases in a gas mixture using particularly, but not exclusively, permeable membranes (28). In passing over a membrane (28), a portion of a gas mixture in intimate contact with the membrane wall experiences a change in density as components of the gas selectively diffuse through the membrane (28). In particular, the present invention uses gravity or other force to act on the density difference created by diffusion to assist in a) "peeling" (away from the wall) the gas which has already undergone substantial diffusion: b) keeping this gas away from the diffusion surface, once it has left; c) removing the gas from the membrane (28) more quickly; and d) slowing gas which has had less exposure to the diffusion process and moving it towards the membrane wall. Embodiments of the invention are described.

Abstract: The heating of submersible hulls, diving suits and other underwater equipment usually involves use of electrical batteries. However, in cold water operations these electrical batteries prove quite inadequate for the task. The invention provides for a self-contained heating system involving the bringing together in a submerged reaction zone of substances capable of reacting together exothermically. Preferably one of the substances is a metal e.g. aluminium in ingot form, and the other substance is an aqueous solution of sodium hydroxide and is fed to the ingots of aluminium. The invention is also apparatus for carrying out the reaction and transferring the heat generated.

Abstract: The risk of lung "squeeze" in use of diving headgear in return-line diving systems arises through the need to subject the exhaust hose to suction pressure in order to withdraw the used gas from the helmet. The usual exhaust regulating valve can quite readily jam, needs considerable servicing, and can only provide the desired high flow rates at the expense of the mechanical advantage which must however be kept high to avoid rendering the valve unduly sensitive to across-the-valve fluctuations.