Performance of life support breathing apparatus for under-ice diving operations

INTRODUCTION: Single-hose scuba regulators dived in very cold water may suffer first- or second-stage malfunction, yielding complete occlusion of air flow or massive freeflow that rapidly expends a diver's air supply. PURPOSE: This study, conducted in Antarctica, evaluated the under-ice performance of a sampling of commercially available regulators. METHODS: Seventeen science divers logged a total of 305 dives in -1.86°C seawater under 6-meter-thick Antarctic fast-ice over two field seasons in 2008 and 2009. Dive profiles had an average depth of 30 msw and dive time of 29 minutes, including a mandatory three-minute safety stop at 6 msw. Sixty-nine unmodified regulator units (17 models) from 12 different manufacturers underwent standardized pre-dive regulator care and were randomly assigned to divers. Depths and times of onset of second-stage regulator freeflow were recorded. RESULTS: In 305 dives, there were 65 freeflows. The freeflows were not evenly distributed across the regulator brands. Regulator failure rates fell into two categories (⟨ 11% and ⟩ 26%). The regulators classified for the purpose of the test as "acceptable" (⟨ 11% failure rate: Dive-Rite Jetstream, Sherwood Maximus SRB3600, Poseidon Xstream Deep, Poseidon Jetstream, Sherwood Maximus SRB7600, Poseidon Cyklon, Mares USN22 Abyss) experienced only nine freeflows out of 146 exposures for a 6% overall freeflow incidence. Those classified as "unacceptable" (⟨ 26% failure rate) suffered 56 freeflows out of 159 exposures (35% freeflow incidence.). CONCLUSIONS: Contrary to expectations, the pooled incidences for the seven best performing regulators was significantly different by Chi-square test from the 10 remaining regulators (P ⟨ 0.001).