Backup System Arrangement

To provide complete redundancy Freebreathe technology has two backup systems. The first backup system is a rebreather incorporated into the diver’s backpack that utilises the gas reclaim double counterlung. A mechanical semi-closed circuit rebreather will last for up to two hours which will comfortably support most in-water decompression profiles. An alternative electronic fully closed circuit rebreather that would last for up to 5 hours could also be made available to support really extreme decompression profiles. This is used if there is a problem with the surface equipment or the umbilical hoses.

The second backup system is a surface supplied open circuit demand regulator. Its duration is dependent on the size of the gas cylinders on the dive platform. This is used when there is a problem with the counterlung.

Umbilical Isolation

In order to ensure that either backup system will operate correctly the supply and return umbilical hoses are isolated from the double counterlung by a dual shutoff valve mounted on the diver’s waist strap or belt. The valve is activated by pushing down on the plunger. For testing purposes the plunger can be released and returned to its original position. The supply hose remains connected to the demand regulator.

Rebreather Activation

The rebreather is activated by pulling on the normally closed triple shut off valve to open up the carbon dioxide scrubber to the return counterlung, the backpack’s medium pressure oxygen supply and the backpack’s medium pressure diluent supply. Once the rebreather is activated automatic valves control the flow of diluent and oxygen into the breathing circuit to maintain the correct partial pressure of oxygen. Again the valve is reversible, allowing the diver to test its operation and then return back to the primary breathing system.

The demand regulator is activated by a commercially available rebreather bailout valve (BOV) which is either attached to the diver’s mouthpiece or the oral nasal mask of his mask or helmet. Again these are reversible, allowing the backup systems to be tested by the diver either before, or any time during, the dive.