Emergency oxygen systems come in various sizes and styles, but most incorporate the same basic elements: a high-pressure oxygen storage cylinder, a regulator/control valve assembly and a delivery mask.

The two primary types of emergency oxygen systems for divers are constant-flow systems and demand systems. Constant-flow systems provide a regulated, and in some cases adjustable, flow of oxygen to the delivery mask. Demand systems provide oxygen in response to the user’s inhalation, thus delivering a higher percentage of oxygen and wasting less gas.