Enriched air nitrox (EANx) compressor systems

Background
What is nitrox?
Recommendation

Background

Earlier this year, an incident occurred within a diving establishment at Port Lincoln, South Australia, which resulted in an explosion of a compressor coupled to a NITROX membrane. The compressor was in use filling a dive cylinder with a 36% oxygen mix and had reached approximately 20 bars at the time of the explosion. The filter assembly was ejected from the compressor into an adjoining room. The immediate area was subjected to extreme heat and there was some damage to the surrounding area. No one was injured; however the potential for severe and/or fatal injuries was high.

Investigation revealed that the explosion originated at the base of the final filter assembly on the second stage compressor. While the exact cause of the explosion has not been established, it is suspected that there may have been a small quantity of oil present within the compressor since overhaul. This oil is believed to have collected within the filter assembly and mixed with the 36% oxygen, which led to the explosion.

Persons handling high pressure oxygen in the production of Nitrox or other gas mixes are at risk of being seriously injured by fire or explosion when unclean or unsuitable equipment or cylinders are used for this purpose.

High-pressure oxygen is extremely reactive and is not compatible with most materials. Many materials, which will not burn in air will be vigorously consumed in pure oxygen once ignited.

Generally, systems used for air will not be acceptable for handling oxygen or mixture with greater than 23% of oxygen.

What is nitrox?

Nitrox is a compressed breathing gas mixture of the gases oxygen and nitrogen, in which, most commonly the oxygen percentage is greater than atmosphere, typically around 30-50% in the mixture.

Recommendation

Owner/operators of similar systems and those involved in decanting oxygen rich mixtures should be familiar with the potential hazards and have an expert understanding of the strict procedures necessary for their safe mixing and use.

Please be aware that the following factors may affect the safety of the process:

Compressor types, the integrity of filtration and cleanliness of the compressed gas
Cleanliness of the components of the scuba system exposed to oxygen
The materials used in the manufacture of the equipment and components
Compatibility of lubricants used within the equipment when exposed to high pressure oxygen or high oxygen concentration mixes
Incorrect assembly of breathing apparatus or filling system

Should there be any doubt as to the suitability of any such systems, owners and/or operators should contact the manufacturer or supplier of the equipment for technical advice.

In addition, the following are strongly recommended:

Filling and decanting systems should be installed operated and maintained by competent persons in strict accordance with the manufacturer and/or supplier's recommendations and requirements
Cylinder filling should be supported by an appropriate quality assurance system
Careful consideration should be given to the positioning of compressors and decanting systems. Where possible cylinders should be filled in an area remote from the public
Where compressors are used consideration should be given to performing regular oil analysis

For further information regarding the filling of cylinders, refer to:

AS 3848 Filling of portable gas cylinders (non-Queensland Government link)

Note: AS 3848 does not cover compression filling of gaseous oxygen. (Nitrox compressor systems)

The information in this alert was provided by the Department for Administrative and Information Services of South Australia.

Last updated July 12, 2005