Fundamental Oxygen Risks Comprehension; The O 4 Concept - POSEIDON Xstream Series Service Manual

aPPENDix B
APPENDIX B

Fundamental oxygen risks comprehension

For a fire to occur, three elements must be present. A fuel, an oxidiser, and an ignition source. If any of these three is non
present, combustion cannot take place. All regulators being used with a gas containing any percentage oxygen, exhibits all
these elements and therefore the risk of a fire is present – ranging from extremely low risk to extremely high risk. The ignitability
of the fuel, the concentration of oxygen, and the number of ignition sources and their likelihood to occur determines the level of
risk exposed.
Everything can combust in an oxygen rich atmosphere, i.e. all materials can be regarded as fuels. Polymers and organic
materials are oftenly more easily ignitable than metals, why they shall be avoided as far as possible in a regulator intended for
oxygen rich mixtures, in order to lower the risk for combustion.
Gaseous oxygen is a strong oxidiser. The higher concentration, the higher temperature, and the higher pressure – the greater
its oxidising properties.
What you as a regulator service technician can do to reduce the risk, is to remove the ignition sources.
•
Particulate
•
Auto ignition
•
Electrical sparks
•
Adiabatic Compression
•
Heat
•
Frictional heat
•
Resonance (heat)
Ideally, if you could remove them all, there would be no risk for combustion.
Particulate material can ignite in at least two ways. A small particulate travelling at high speed in a geseous stream can, when
it hits a surface, create either a spark or transfer enough energy to trigger the absorbing materials auto ignition temperature. Or
second, since a cluster of particulate material exhibits a large surface area, it can pick up e.g. resonance heat more effectivcely
and thereby reach its own AIT. Particulates must therefore be removed effectively.
All materials have a threshold temperature upon reached the material will start to burn automatically, the Auto Ignition Temperature,
AIT. The AIT depends on oxygen concentration, such as at a higher concentration the lower threshold. Hydrocarbons (oil,
fingerprints, grease) have a very low AIT, and are almost certain to combust in an oxygen rich environment at high pressures.
Combustion, if it occurs, can be anything from unnoticeable to catastrophic. A low mass of e.g. some Nylon-like plastic materials
will only produce fumes containing carbon-dioxid and water. Other plastics, e.g. viton, will produce hydroflouric acids, which
even in extremely low concentrations can kill a diver if inhaled. Viton has a significantly higher AIT than Nylons, why it is far less
likely to burn if compared in exactly the same situation. But the effects if it happens in a regulator is far worse.
Different materials when burning releases different amounts of energy. Hydrocarbons have a high heat of combustion. The
produced heat can in turn act as an ignition source for less ignitable materials, producing what's referred to as a kindling chain
reaction. Thereby, the presence of materials with low AIT and high HC, can ignite the nextcoming part downstream, which in
turn possibly can ignite...etc.
There are no level of percentage of oxygen which can be guaranteed as safe. There are only factors which increases or
decreases the risk for combustion.

The O 4 concept

Poseidon has introduced the O
approved.
O 1 In short, oxygen engineered is taking every step to lower both the risk for combustion and the possible effect of
combustion. The design must reduce the number of ignition sources, allow effective maintenance and cleaning,
materials must be selected as to break kindling chain reactions, constructed to minimise effects of compression
shocks etc.
O 2 Oxygen compatible is selecting materials which have the best combination of AIT, HC, OI, and the severity of a
possible failure for its function in the sytem.
O 3 Oxygen clean means that either a component or a complete system is cleaned from especially hydrocarbons and
particulate to a level which gives an acceptible risk for ignition.
O 4 Oxygen approved means the product has passed tests conducted by independent organisations according to
international standards.
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concept, which stands for oxygen engineered, oxygen compatible, oxygen clean, and oxygen
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