Most recreational scuba sets have a backup second-stage demand valve on a separate hose, a configuration called a "secondary", or "octopus" demand valve, "alternate air source", "safe secondary" or "safe-second". This arrangement was intended to reduce the problems of buddy breathing from a single demand valve and has become the standard in recreational diving. By providing a second demand valve the need to alternately breathe off the same mouthpiece when sharing air is eliminated. This reduces the stress on divers who are already in a stressful situation, and this in turn reduces air consumption during the rescue and frees the donor's hand.
Most recreational scuba sets have a backup second-stage demand valve on a separate hose a configuration called a "secondary" or "octopus" demand valve "alternate air source" "safe secondary" or "safe-second" This arrangement was intended to reduce the problems of buddy breathing from a single demand valve and has become the standard in recreational diving By providing a second demand valve the need to alternately breathe off the same mouthpiece when sharing air is eliminated This reduces the stress on divers who are already in a stressful situation and this in turn reduces air consumption during the rescue and frees the donor's hand