A system recommended by some organisations, mostly those involved in technical diving (GUE, CMAS-ISA, other tech and cave diving groups) is to equip the regulator normally used throughout the dive (the "primary") with a long hose, typically long, proportional to the height of the diver. This is the regulator that is donated to a diver who is out of air. The "secondary" or "backup" regulator is then reserved for the donor diver and is on a short hose, suspended just under the chin by a "necklace" that can break free in an emergency. The principal advantage is that the diver who is in trouble receives a regulator that is known to be working and provides breathing gas appropriate for the current depth—and quite possibly gets air more quickly than if the clipped off octopus were donated. Donation of the long hose is particularly beneficial for cave and wreck penetration diving where divers sharing air may need to pass through small openings, as the hose length lets them swim in single file where necessary. The length of the hose also allows the divers to swim side-by-side or one above the other in all possible arrangements. Another advantage is that the secondary regulator stows out of the way, protected from strong water flow, contamination and snags, and where the diver can notice if it leaks—but remains accessible without requiring the use of hands, as divers can pick up the mouthpiece by dipping their chin. This arrangement is slightly more cumbersome to use and requires greater skill to wear, deploy and recover. Benefits may not outweigh disadvantages for open water divers in relatively low hazard conditions.