1.1 Chassis & Fundamental Configuration
The basic envelope and fundamental configuration of any rebreather device includes several simple principal elements.
The placement of hardware may occur anywhere on the diver (back, front, side), or exterior to the diver (as a stage, mounted to a vehicle, or other platform) but must make best efforts to protect sensitive components such as hoses, counterlungs, cables, and other soft parts from snagging, abrasion, or restrictive operations.
In all cases, component hardware is affixed to a centralized chassis, which should be suitably ruggedized for its intended purpose. The frame or chassis provides effective means to fix the rebreather apparatus to the desired harness, backpack, or other mounting platform, and should allow for easy disassembly for cleaning or stowage. Frankly, it is highly irrelevant whether the chassis is made of plastic, aluminum, a composite, or soft pack as these are simply features of an assemblage and do not speak to any specific technology.
RD1 chassis components | Lombardi Undersea
Good practice is for the chassis to account for an overall gas configuration which follows the technical diving convention of ‘Rich on Right, Lean on Left’ where the supply and controls for oxygen-rich gas are found on the diver’s right side and controls for diluent or oxygen-lean gas are found on the diver’s left side. Likewise, oxygen cylinders or oxygen-rich cylinders are placed on the diver’s right side, while oxygen lean(er) gas is placed on the diver’s left side. This aids in tactile identification of all systems and takes advantage of the engrained best practices from mainstream technical diver training. Rich on right, lean on left, is a good rule - its time tested, intuitive, and a good standard of operational practice.
Further, when multiple diluent gases are used, the shallow gas is ‘up’ and deep gas is ‘down’ with regards to the relative placement of each cylinder and/or their control knobs or valves. Again, this aids in tactile identification of all system functions and provides intuitive operation for the diver. When multiple diluents are carried offboard, they should similarly follow the ‘[oxygen] rich on right, [oxygen] lean on left’ mantra. More on gas distribution specifics will be addressed in subsequent sections.
Of paramount importance when fitting all of the parts and pieces together is that there should be sufficient space for the counterlungs to expand and contract freely with each breath, without restriction by other hardware affixed to the chassis or exterior rigging components.
When accepting that these basic unit specific configurations are largely consistent from unit to unit to a great degree, it is then irrelevant where or how a unit is donned and carried through a dive. Any assumption that unit A is better than unit B because of how or where it is configured is a misunderstanding of the core envelope of the system as any unit can be broken down and re-configured for alternate positioning with minor adjustments or adapters. Interestingly, this ‘tinkering’ has resulted in a substantial underground or black market of aftermarket accessory components. In many cases, it is only simple desired design features or cosmetics that differentiate one unit from another – the core technology and fundamental envelope is the same – i.e. fundamental rebreather technology is fundamental rebreather technology.