For purposes of rescue during cave diving, Exley helped standardize the usage of the "octopus", a redundant second stage diving regulator that can be used as a backup in the event the diver's primary second stage fails, or alternatively, to allow the diver and his buddy to have simultaneous access to the diver's gas if the buddy has an out-of-gas emergency. The octopus is now considered an essential piece of equipment among virtually all scuba divers, whether caving or in open water.