Which hazard gas forms when welding over brake cleaner residues?

• A. Phosgene gas
• B. Chlorine gas
• C. Ammonia
• D. Nitrogen dioxide

Answer: (A)

Phosgene gas forms when welding over brake cleaner residues because brake cleaner contains chlorinated solvents that decompose under the heat of the weld to form phosgene (COCl2), a highly toxic choking gas. This is the classic hazard teachers emphasize when residues of chlorinated cleaning agents are heated by welding. Protect yourself by removing residues with non-chlorinated cleaners and ensuring good ventilation before welding. Chlorine gas, ammonia, and nitrogen dioxide aren’t the typical products of welding over brake cleaner residues in this context.