or a mission, the saturation diving team is decompressed gradually back to atmospheric pressure by the slow venting of system pressure, at an average of to per day (schedules vary). The process involves only one decompression, thereby avoiding the time-consuming and comparatively risky process of in-water, staged decompression or sur-D O2 operations normally associated with non-saturation mixed gas diving. More than one living chamber can be linked to the transfer chamber through trunking so that diving teams can be stored at different depths where this is a logistical requirement. An extra chamber can be fitted to transfer personnel into and out of the system while under pressure and to treat divers for decompression sickness if this should be necessary. The divers use surface supplied umbilical diving equipment, utilizing deep diving breathing gas, such as helium and oxygen mixtures, stored in large capacity, high pressure cylinders. The gas supplies are plumbed to the control room, where they are routed to supply the system components. The bell is fed via a large, multi-part umbilical that supplies breathing gas, electricity, communications and hot water. The bell also is fitted with exterior mounted breathing gas cylinders for emergency use. While in the water the divers will often use a hot water suit to protect against the cold. The hot water comes from boilers on the surface and is pumped down to the diver via the bell's umbilical and then through the diver's umbilical. The transfer chamber is where the bell is mated to the surface saturation system for transfer under pressure (TUP). It is a wet surface chamber where divers prepare for a dive and strip off and clean their gear after return. Connection to the bell may be overhead, through the bottom hatch of the bell, or lateral, through a side door. The accommodation chambers may be as small as 100 square feet. This part is generally made of multiple compartments, including living, sanitation, and rest facilities, each a separate unit, joined by short lengths of cylindrical trunking. It is usually possible to isolate each compartment from the others using internal pressure doors. Diving bell A closed diving bell, also known as personnel transfer capsule or submersible decompression chamber, is used to transport divers between the workplace and the accommodations chambers. The bell is a cylindrical or spherical pressure vessel with a hatch at the bottom, and may mate with the surface transfer