Emergency advice needed - welding near fuel tank

[Treeman612]

Hi folks - I'm rebuilding the whole back end of my 320i, and when taking out axle carrier/diff/rear arms I noticed rusty inner wheel arch on off side. New inner arch section arriving 2morrow. What is the plastic bottle thing behind the wheel arch plastic cover on the offside? - looks like some sort of expansion/evaporation tank for the fuel filler?
I'm going to be MIG welding the new arch in - am I in danger of blowing myself up welding this close to the filler cap and this bottle thing/
Sod's law, the fuel tank is 90% full, so I really don't want to drop the tank etc if I can avoid it, but ANY good advice will be seriously welcome. Cheers

[Jos]

Drain the tank and drop it seriously! It's not worth the risk welding with that amount of fuel anywhere near you. 40l of petrol will burn your car to the ground and I seriously doubt an extinguisher is going to help you with a fire that size. There is also the danger the vapour will catch and explode in which case you won't actually be around to attempt to put the fire out.

Drain it and drop it..

[karlp]

It will not take you long to drop the tank.

No question - remove the tank as Jos says - anyone who says otherwise is a prat.

karl

[A1BMW325iSport]

as the others say, safety first mate!