Published: 6 June 2017
This safety alert highlights the dangers associated with the production of Nitrox, including the oxygen stick method.
The oxygen stick method, also known as continuous gas blending, involves mixing a continuous flow of pure oxygen with ambient air in a chamber, directly connected to the high-pressure compressor inlet for compression.
Earlier this year, a Queensland diving business producing Nitrox had a significant incident. The compressor, producing Nitrox at 36 per cent via the oxygen stick method, had filled approximately eight dive cylinders and was in the process of filling another when an explosion and fireball occurred.
Components of the oil/water separator were blown off the compressor and there was extensive damage to the compressor and surrounding structure. Parts of the adjoining premises were also damaged. No one was injured in the incident, but there was a high risk of workers or others being killed or severely injured.
The reason for the explosion has not been established, but likely contributing factors include:
- oil residue throughout the internal surfaces of the compressor unit, which in combination with high levels of oxygen and high operating temperatures may have exploded.
- a recently installed second hand compressor, not approved by the manufacturer for the production of Nitrox
- the highly reactive nature of high-pressure oxygen and the materials present, which can be consumed in a pure oxygen environment, once ignited.
Owner/operators using Nitrox compressors or decanting oxygen rich mixtures should be familiar with the hazards and have a thorough understanding of the procedures for safe use.
The compression and filling process can be affected by:
- compressor types, the integrity of filtration and cleanliness of the compressed gas
- compatibility of lubricants used within the equipment when exposed to high pressure oxygen, high oxygen concentration mixes above 23 per cent and high operating temperatures
- cleanliness of the components of the system exposed to oxygen
- the materials used in the manufacture of the equipment and components.
If there is any doubt about the system's suitability, the owners and/or operators should immediately contact the equipment manufacturer or supplier for technical advice.
It is strongly recommended to:
- have competent workers install, operate and maintain filling and decanting systems in strict accordance with the manufacturer's or supplier's recommendations and requirements
- locate the compressor and decanting systems away from public areas
- make sure production processes for Nitrox and cylinder filling are supported by an appropriate quality assurance system and documented operating procedures.
For further information regarding the use of Nitrox refer to: