Welding on vehicle safety issues?

Jul 19, 2006
MS Gulf Coast
I need to patch floor panels in my FJ55. I've taught myself to weld and have practiced joining sheet metal several ways. What I don't know are the safety issues when using cut off, grinder, or welder on the vehicle.

Does the risk of generating sparks while doing any of the above require removing the gas tank from the vehicle? Is that the 100% of the time answer or are there safe mitigations. I'm not looking to cut corners-just don't have any appreciation for what the standard is.

Thank you.
May 28, 2017
in the woods
@GJCruiser , if your fuel system is intact, i.e. no leaks anywhere, tank, filler neck, fuel lines, vent lines, you shouldn't need to remove the tank. if you're working in the cargo bay, i'd drop the tank, more for ease of repair. mind you, it does cut back on the "oh $h!t" factor if a sawzall blade or cutting disc gets out of control. what i do is map my cuts from underneath with self tapping screws marking the corners. then the underside gets cleaned of any undercoating n such about 2" on the outside of the cut n about 1" on the inside. i've had undercoating ignite with grinder cutting disc.
in the footwells, just make sure you know what is underneath n where it is. for those areas i probably wouldn't drop the tank. just doing your due diligence should keep your repairs from making headlines in the local evening news :hillbilly:
Feb 7, 2015
Eastern Washington
Main issues with cutting and welding panels while on vehicle are:
1) knowing what's on the other side of the panel you're working on. Make sure you keep wires, fuel, brake and other lines protected from excessive heat and damage. I typically put a scrap piece of sheet metal between the area I am working on and the line for this purpose. Try to leave a little air gap between your work panel and the scrap sheet to reduce heat transfer.
2) fire from paint, grease, or coatings. Try to remove as much of these things as you can within a few inches of your work area, particularly before welding. Keep a fire extinguisher nearby. Some can also produce some nasty smoke/fumes so be cautious of that and work in a ventilated area. Also remember that the fire could start up on the inside of enclosed area where you can't see it so pay attention for excessive smoke build up.
3) if you are working near the fuel tank or the ends of vent lines be wary of vapors. Try to plug the vent line temporarily if you can and be sure you have plenty of air movement. I've done work with the fuel tank in the vehicle with fuel in it and been ok. If removal of the tank is an easy option it's probably the safest. You could also pump out all of the fuel and let it sit several days to vent and that would help too.

Another non-safety issue to be aware of is damage to glass panels. The sparks from cutting, grinding and welding will etch your glass and ruin it. Be sure to cover any glass with a welding blanket (or cardboard if you can't find anything else). Same goes for paint if you care about keeping it.
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