text: Much of the confusion appears to be a result of misapplying PVHO (pressure vessel for human occupancy) guidelines which prescribe a maximum ambient oxygen content of 25% when a human is sealed into a pressure vessel (chamber). The concern here is for a fire hazard to a living person who could be trapped in an oxygen-rich burning environment.
  Of the three commonly applied methods of producing enriched air mixes – continuous blending, partial pressure blending, and membrane separation systems – only partial pressure blending would require the valve and cylinder components to be oxygen cleaned for mixtures with less than 40% oxygen. The other two methods ensure that the equipment is never subjected to greater than 40% oxygen content.
  In a fire, the pressure in a gas cylinder rises in direct proportion to its absolute temperature. If the internal pressure exceeds the mechanical limitations of the cylinder and there are no means to safely vent the pressurized gas to the atmosphere, the vessel will fail mechanically.  If the vessel contents are ignitable or a contaminant is present this event may result in a "fireball".
  Incorrect gas mix
  Use of a gas mix that differs from the planned mix introduces an increased risk of decompression sickness or an increased risk of oxygen toxicity, depending on the error. It may be possible to simply recalculate the dive plan or set the dive computer accordingly, but in some cases the planned dive may not be practicable.