Rebreather Setting Leads to Dangerous Equipment Failure

Photo by Stephen Frink


  • Diver had been diving with JJ closed-circuit rebreather for one week prior to trip.
  • Regulators were professionally serviced before the trip.
  • Seemingly minor issues led up to a major line pressure failure.
  • Diver troubleshooted the issue and finished the dive safely.

Reported Incident

Before a recent trip to Truk Lagoon, I had been diving with my JJ closed-circuit rebreather (CCR) for one week. I’d had my regulators professionally serviced before leaving for the trip. During the first week of the trip, I had an issue while on a dive in which my solenoid stopped injecting oxygen. I was still able to add oxygen manually and complete the dive safely. I had not changed the solenoid batteries before the trip, so after returning to shore and troubleshooting the issue I attributed it to dead batteries. After exchanging the batteries for a spare set I had with me, the unit tested fine, and I successfully dived it the next day.

Two days after the initial failure, the same issue occurred, and the dive was safely completed using the rebreather’s manual add valve (MAV). I troubleshot the unit when back on shore, and all was working normally. I elected to dive it again after I changed the batteries again with another set bought by another person. The following day the solenoid failed once again in the same manner. Another diver asked if I had checked the line pressures of the regulators. I had not. Upon returning to shore, I tested the regulator line pressures and found that both the oxygen and diluent regulators were set to 10 bar. When I consulted the operating manual online, I found that the line pressure of the oxygen regulator needed to be set at 7-7.5 bar. At this point, the next dive was leaving soon, and I elected to do the dive and wait until later to adjust the regulator.

During the next dive, at approximately 34 meters (112 feet) and inside the wreck, I heard what sounded like gas flowing behind me. I was aware that my buddy was in that direction and briefly thought it was coming from him. Approximately 5-10 seconds after the sound began, I started to notice my cheeks puffing outwards and my buoyancy gradually changing. At this point, I checked my controller and noted my ppO2 was at 3.08. Using my light, I signaled to my buddy that there was a serious problem. I diagnosed a high-oxygen problem and disconnected the MAV; the noise stopped. Next, I elected to bail out to my 11-liter (80-cubic-foot) air cylinder and quickly exited the wreck through nearby hull damage. My buddy joined me shortly afterward, I shut down the O2 valve, and we ascended to the anchor line, where I completed deco using open-circuit air and 50 percent O2 with no adverse outcomes. Following some witty banter on the return boat trip, I adjusted the O2 regulator to the correct line pressure, changed batteries again, and no further issues occurred for the remainder of the trip.

I now check my line pressures before every dive on every regulator I will be using.


Erroneous settings of regulator line pressure at recent services of the gear caused a serious CCR failure that could have been fatal. The diver failed to diagnose and fix the problem, which had occurred during three previous dives. Having his buddy nearby may have saved his life. He drew an important conclusion in adding line pressure checks to his routine predive equipment checks. 


It is important when getting gear serviced to specify what kind of diving that gear is used for. Servicing for regulators varies on the brand and type of equipment, so making sure the technician knows if it will be used on a close-circuit rebreather could have prevented an irregular pressure setting. It is always best before diving to double check your apparatus and check your line pressures to make sure they are compatible with your brand of equipment.