| Varying O2 Flow
Three axioms of mixed gas Rebreather diving are: 1) In RB diving, the risks, failure modes & effects, and consequences of a dosage subsystem failure are typically, substantially greater than with OC diving; 2) a dosage subsystem (first stage and / or dosage device) 'failure' can occur at ANY time, ie pre-dive, diving, or post-dive. and are typically more insidious and less easily detected than in OC rigs, and 3) death is permanent.
CCR Drivers, and especially MCCR ones should develop a disciplined procedure and schedule for 'testing', and 'checking' the flow rates of their units, where the mandatory schedule is much more frequent than the 'at least once per year' cited in a previous post.
Flow rates should be 'tested', with flow meters, 1) after each period of storage, 2) certainly weekly, and preferably daily, during periods of active diving, and 3) before each very deep or critical dive that may tax their 'bailout mix' duration.
MCCR Drivers should also define a 'quick check' procedure to verify approximate flow rates, certainly pre-dive on each diving day , and preferably before each dive. Each diver should define the procedure that is best suited to themselves and their equipment. One of the most common is to 'suck down' the breathing loop, close the DSV, and clock the time required for the controlled mass flow to refill the breathing loop up to 'full counterlungs'. This 'check time' should be compared with previous ones, where the flow rates have been verified with a flow meter. Some divers prefer to clock the time to 'cracking' (start of venting) of the OPV (altho when the OPV cracks is sometimes not so easy to detect). This procedure also serves to confirm that the OPV is not 'stuck'.
Good Safe Diving
Dan |