Purging is the removal of all unwanted gas or vapour from an environment by displacement or dilution with nitrogen.

The most certain method of purging a vessel with nitrogen is by dilution. Nitrogen purging is used where the oxygen concentration within an environment needs to be reduced, where a flammable gas or vapour needs to be removed, where atmospheric air is to be removed or where air ingress must be prevented.

Applications for the technique include:

• Providing an inert atmosphere in a container or pipeline prior to filling with a toxic, flammable or explosive material.
• Reducing the level of toxic, flammable or explosive atmosphere in a container or pipeline prior to work being undertaken.
• Back purging to protect welds from contamination.
• Purging of pipelines and containers to eliminate atmospheric contamination during welding operations.

Purging may be carried out with gas in several ways including, use of a pressure cycle, use of a vacuum cycle, or at atmospheric pressure.

Foam inerting may be used to displace a flammable atmosphere with nitrogen when welding or cutting has to be carried out in a vessel.

Careful control of the process and accurate monitoring are essential if desired results are to be achieved.

When purging containers or pipelines, oxygen deficient environments may be created. It is important to fully understand the asphxyiation risks and take the correct precuations prior to undertaking work.

BOC Cryospeed has a wide range of personal and fixed oxygen deficiency monitors that will ensure a safe working environment.

Our highly trained BOC Cryospeed Sales and Service Operators can offer advice on the associated risks as well as on our range of oxygen monitors.