1) Underwater breathing apparatu 
A bailout bottle, bailout cylinder or emergency gas supply (EGS) is a scuba cylinder carried by an underwater diver for use as an emergency supply of breathing gas in the event of a primary gas supply failure. A bailout cylinder may be carried by a scuba diver in addition to the primary scuba set, or by a surface supplied diver using either free-f...
is a cylinder with an emergency supply of air or other breathing gas, aimed to use in case of air supply trouble.