My favorite Car-Talk puzzler was--A guy removes his spark plugs and uses a
vacuum cleaner to clean the dirt out of the spark-plug well. Q: How long was
it before the widow remarried?

Using a shop vac to suck fumes is suicidal.

Real macho fuel tank oxy-acetylene welders use another trick--They purge the
gas tank with propane or natural gas, plug the vents, then they ignite the
leaking gas to show where the cracks are. This makes the job very easy AND
very safe.

Liquid fuels are characterized by an LEL  Lower Explosive Limit (Gasoline)=
1.3% volume (saturation) and a UEL Upper Explosive Limit of 7%. This all
gets more complicated with temperature and pressure changes.

But for the normal airplane on the ground the situation is not so
complicated. As long as there is liquid fuel in the tank, there may be a
fire hazard but not an explosion hazard. People do use gasoline in wick-type
lanterns. It's not so different from kerosene.

Two issues are involved in construction: Grounding and bonding. Bonding is
making sure all parts are attached with conductors to have the same
potential. Grounding is sending this potential to real ground. If it were my
airplane I would use some carbon fiber (conducts a little) strategically
placed to bond all fuel tanks and dissipate everything to the landing gear
and some place the fuel truck can clip onto. That's not perfect but it's as
good as one can practically get.

Fly and fuel safely!
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge MA 01550-2705
Phone (508) 764-2072
Email: emjones@charter.net