I learned about Phosgene gas when I took a welding coarse twelve years ago.
You can also get it by welding a painted surface. The burning paint will release it. Also if the paint has lead in it. You will have additional problems.
Always wear a respirator mask with charcoal when welding. No matter how small the job is. Weld in a well ventilated area.
The other side effect is nerve damage.
You don't need a weed killer, if you have a Backhoe.