Redundant Air System : An independent secondary underwater breathing system (i. e. , a pony bottle with first and second stage, or a pony bottle supplying a bail-out block)
NFPA 1670 Standard on Operations and Training for Technical Search and Rescue Incidents, 2009 ed. https://www.nfpa.org/assets/files/AboutTheCodes/16 70/Errata1670-09-1.pdf, (Std: Opr and Trng for Tech Search and Rsq Incid - Amer) {408 NFC}