It's the fumes that get you in a fuel tank.
Gas, diesel, oil, anything oil based will expand and head for the hole you are trying to plug.
Clean the tank with brake cleaner then with water and detergent.
Fill it with water then fix the hole.
Nitrogen is another option.
Old gas tanks even after washing out will have fumes. We would lay the tank in the sun then after an hour light a torch and drag it past the filler neck. Out of 5 tanks we ballooned 3.
Even stuff that doesn't easily burn will rapidly expand when heated.
Corn starch will burn if you stir it up with air then apply a spark.
Even if there is no spark/flame you are heating the material, metal or plastic enough to release chemicals out of the pores.
Air can expand enough to blow your filler material out at you and your eyes etc.
I ain't sayin don't do it just be aware.
I have blown up a bunch of stuff in my 61 years.
Bamboo thrown in a fire will throw splinters out that will stick into your arm.
