Posted By Paul Leadbetter
Andrew
Have you read HSG204 - Health and Safety in Arc Welding? Of the HSE guidance documents that I have, it is the only one that considers hazards other than the high temperature and the use of flammable gases and oxygen at high pressure. Use of shielding gases in confined spaces increases the risk of asphyxiation (besides that from the combustion gases).
Considering galvanised steel in particular, the zinc coating will be burnt off from the workpieces and inhalation of the metal fume could cause metal fume fever (the symptoms resemble 'flu and will probably come on when the welder is at home but be gone by the following morning).

REGARDS

Paul Leadbetter