In technical diving donation of the primary demand valve is commonly the standard procedure, and the primary is connected to the first stage by a long hose, typically around 2 m, to allow gas sharing while swimming in single file in a narrow space as might be required in a cave or wreck. In this configuration the secondary is generally held under the chin by a loose bungee loop around the neck, supplied by a shorter hose, and is intended for backup use by the diver donating gas. The backup regulator is usually carried in the diver's chest area where it can be easily seen and accessed for emergency use. It may be worn secured by a breakaway clip on the buoyancy compensator, plugged into a soft friction socket attached to the harness, secured by sliding a loop of the hose into the shoulder strap cover of a jacket style BC, or suspended under the chin on a break-away bungee loop known as a necklace. These methods also keep the secondary from dangling below the diver and being contaminated by debris or snagging on the surroundings. Some divers store it in a BC pocket, but this reduces availability in an emergency.