FAWLEY refinery has activated a safety procedure known as flaring following what ExxonMobil is describing as "an interruption in operations".

People living near the huge-petro chemical complex on the western shores of Southampton Water say dense black smoke is billowing from the flare stacks.

In an online message to residents ExxonMobil says: "At present we are flaring due to an interruption in operations.

"Flaring is a safe, controlled and environmentally-approved way of burning off excess gas which would normally be recycled and used in our operating processes.

"Our teams are working this issue and we will resume normal operations as soon as we are able.

Daily Echo:

"We apologise in advance for any concern and inconvenience that the flaring may cause to our local residents and thank you for your patience and understanding."

The flaring process is described in detail on ExxonMobile's website.

"A flame burning at the top of one of the plant’s highest towers might look alarming, but in fact it is an important part of its operation," it says.

"It is not uncommon for people to be concerned when they see smoke or flames coming from the tower, called the flare stack.

"However, the flare is a normal and vital part of keeping the plant running safely during unplanned operational interruptions or scheduled maintenance.

"The flare acts as a safety valve for the plant. During normal operations, crude oil is refined to produce a variety of products. However, during an interruption, such as an unplanned loss of power, the system is occasionally unable to continue its processing and excess hydrocarbons are routed through the flare system.

"There, the vapours are combined with steam and burned off; ensuring maximum combustion of hydrocarbons, while minimising emissions into the air.

Daily Echo:

"The Fawley site has four flare stacks. When used on cloudy nights, light from the flares can reflect off the clouds, which can then be seen in the local communities.

"Flaring can occasionally lead to a rumbling sound, similar to distant thunder, resonating from the system. The rumbling is the result of the turbulent mixing of vapours during the flaring process."