Operational Considerations for the Standby Diver in CUMA Dives

The Canadian Underwater Minecountermeasures (MCM) Apparatus (CUMA) is a self-contained, semi-closed circuit breathing apparatus in service with the Canadian Forces (CF) and other North Atlantic Treaty Organization (NATO) Navies for MCM diving to a depth of 81 metres of seawater (msw) using a mixture of helium and oxygen. Current CF rules state that a diver completing more than 30 minutes (min) of oxygen decompression has to be accompanied by a standby diver at the 9 metre decompression stop. As there are no specific repetitive diving rules governing such shallow dives on CUMA, the procedure of adding bottom times to determine the decompression requirements of a second dive must be used. As a result, the standby diver may become unavailable for a subsequent dive to deeper depths. This affects the operational ability of a small team to continue diving as the divers, including the standby become dived out too quickly. Experimental dives to 9 msw to simulate a standby diver accompanying a CUMA diver were conducted in the DRDC Toronto Dive Research Facility to measure the inspired partial pressure of oxygen (PiO2). The results showed that the time-weighted average PiO2 after 30 min at 9 msw was greater than 1.3 atmospheres (absolute) (ATA). As a result, the inert gas loading should be minimal and there should be little or no decompression penalty associated with the standby diver diving again as a working CUMA diver. This will increase the operational ability of a small dive team to continue diving operations.