In confined spaces, welding can be much more dangerous. With less fresh air, toxic fumes and gases can be much stronger. Shielding gases, like argon, can displace the oxygen and kill you.
Stainless steel contains nickel and chromium.
Nickel can cause asthma. Nickel and chromium can cause cancer. Manganese can cause Parkinson's disease, which cripples the nerves and muscles. It feels like the flu and goes away in a few hours or days after exposure ends. Welding through or near some solvents can produce phosgene, a poisonous gas.