We are looking to carry out welding activities on a oil production site which is currently live.

The area the works will be conducted has been reduced from a zone 2 hazardous area to normal non hazardous environmental conditions.

However, going through the risk assessment process, we have highlighted a potential risk from a hazardous flammable vapour cloud from the live area of the plant. We are also looking at dispersion calculations and likely wind direction to help quantify and mitigate the risk.

With the control measures we have in place, we can mitigate against spark ignition potential from grinding and welding operations; however we have a concern that the use of post weld heat treatment blankets can reach temperatires in excess of 600 degreed centigrade, which also happens to be above the prescribed auto-ignition temperature of sour gas (predominantly methane)  of around 600 degrees centigrade. These blankets cannot reduce their working temperature quickly enough to avoid the potential of auto-ignition should a flammable gas cloud disperse intothe woking area and we are thinking of using forced air habitats.

I would be very interested to hear from anyone who has experience of this and could provide some additional guidance or share their experiences.