gas to remove the water. Bringing the casualty to the surface If a diver is out of gas and is breathing gas supplied by the rescuer, the rescuer and casualty must remain close to one another and ascend together. Starting the ascent may be complicated by the casualty's lack of gas to inflate the buoyancy compensator to become buoyant at the start of the ascent and later, at the surface. At the start of the ascent the casualty may need to fin upwards and keep pace with the rescuer until, with the drop in ambient pressure, the gas already inside buoyancy devices such as the buoyancy compensator or diving suit, expands and provides sufficient buoyancy. If the casualty is not capable of making an ascent, due to injury or unconsciousness, or the casualty cannot make a safe and controlled ascent, perhaps due to the loss or damage of the diving mask, the rescuer must control the casualty's ascent. This may be done by using the Controlled buoyant lift. As the casualty is totally dependent on the rescuer, it is important if the two were to separate underwater the casualty should continue to ascend to the surface in a failsafe way. The options for making the casualty buoyant include: inflate the casualty's buoyancy compensator to lift off the seabed, then vent it to make a controlled ascent. If the casualty's buoyancy is maintained slightly positive and the rescuer remains slightly negative, the casualty will not sink if they must be released. inflate the casualty's drysuit, if one is worn, to lift off the seabed, then vent it to make a controlled ascent. A drysuit is a less secure buoyancy device than a buoyancy compensator, and more difficult to inflate if the connected hose has no pressure on it. drop the weights from the casualty's diving weighting system. This may result in a dangerous and rapid ascent. lift, by finning, the casualty into shallower water, or to a shallower depth, where gas in the casualty's buoyancy devices and diving suit will expand, then vent it to make a controlled ascent. It is possible to use the rescuer's buoyancy compensator to lift both divers. A technique for this is taught by some agencies, in which the rescuer holds the casualty with their legs wrapped round the torso, freeing the hands for buoyancy control. This technique does not allow the rescuer to provide upward