Our company background is high pressure oxygen systems, and as such it is standard practice and indeed necessary that the supplier give clients the full technical details on the hose supplied, for reasons of safety. In industrial use high pressure oxygen service safety requires a full material, manufacture, cleaning, inspection and packaging to be specified. The SCUBA industry should be no different, but sadly isnt.
Thermoplastic hose used for oxygen service is either SAE 100R7 or SAE100R8 specification. The hose ends are either a two part quill with separate collet crimped together or pallet swaged or when using a singe part end fitting they are crimped with a die and pusher. During connection NO OIL is used in the assembly, only suitable oxygen lubricants, and after the assembly is cleaned and certified for oxygen.
High pressure oxygen at >3000psi is very thick and viscous and oxygen at high pressure is magnetic so builds up an electrical static load. For short lengths, and low gas velocity the standard black hose can be used, however for long hose lengths and for high gas velocity, large bank trans filling, gas transfer etc it is common practice to use an orange non conductive polymer outer cover. This is to avoid static build up in the hose that when the static is discharged can spark off an oxygen fire. For light gases including helium it is also common to have the outer thermoplastic layer pricked to avoid gas bumps in the outer cover as the gas migrates through the polymer inner core and braided cover but builds up under the outer protective polymer jacket.
The difference between R7 and R8 in application is the working pressure and safety burst pressure. Normally 4:1 is used for oxygen so requiring a 25,000psi minimum burst at 4:1 the R8 is specified. To allow a smaller bend radius and a more flexible hose arrangement Kevlar is the inner braid of choice. The system and pipe runs should be earthed and a continuity check should be done to avoid static build up.
For safety a 2mu in line filter should be used at the start of the system to avoid spontaneous ignition due to high particle velocity and particle impingement, and the pipe runs should never terminate in the branch of a tee. Adiabatic compression is the other problem with flexible filling whips so it is also comment to run a small coil of Tungum, alpha brass or copper tube to act as a heat sink at the charged end at the point of adiabatic compression. Never use steel or stainless steel tubing at this end.
Although stainless is used in HP low velocity pipe work applications such as inside a compressor it is never used in the high velocity areas such as panels, and long distribution lines. As I dont see much difference between US and EU in safety requirement with oxygen and the gas appears to behave similar on both sides of our planet I hope this European version helps. Iain Middlebrook.
