Does Pre-breathing your rebreather matter?
July 16, 2015 4:07 pm / Category: Uncategorized
Training agencies and rebreather manufacturers have advocated pre-breathing the rebreather prior to diving. The rationale has been that CO2 bypass and scrubber faults can be detected prior to jumping into the water. As one instructor told me: “Better to pass out on the boat deck than underwater”. This practice appears to have common sense but does it actually pan out?
A randomized single-blind study from March 2015 on the subject drew the following conclusions:
While pre-breathes are useful to evaluate other primary functions;
The five-minute pre-breathe is insensitive for CO2 scrubber faults in a rebreather. Partly failed conditions are dangerous because most will not be detected at the surface, even though they may become very important at depth.
The trials included 20 pre-breathe tests of five minutes for each condition. A Inspiration Evolution Plus rebreather was used with:
Partly failed scrubber
- With a normal scrubber, nobody terminated.
- With a partly failed scrubber, 2/20 terminated.
- With an absent scrubber, 15/20 terminated which means that 25% of divers DID NOT TERMINATE.