This is a bit outside my comfort zone.......

Subcontractor on a construction site has been told by site manager to cease welding work until the operator has full RPE in the form of air fed respirator. The subcontractor is asking whether this is necessary.

Details are a bit vague but I believe the activity is gas welding of standard mild steel and being carried out outdoors.

I have explained that PPE/RPE would normally be determined by risk assessment and dependent on the nature of the materials being welded and the hazardous nature of the fumes generated (it does not appear that there is a risk assessment in place). I have also explained that the site manager is complying with his duties to ensure that work activites are being carried out safely and with the correct PPE, but he MAY be asking for more than is required. I have suggested the subcontractor asks the site manager for his rationale in requiring the high level of protection.

What protection would one normally expect for gas welding of mild steel outdoors?

Many thanks

Gas welding usually produces little fume, so if the material is indeed mild steel, without anything nasty on the surface (lead, zinc, etc), the measures asked for seem a bit OTT.

Gas welding does need good ventilation - you can get significant quantities of oxides of nitrogen, but this is usually only a problem in a confined space.

For a simple mild steel, good general ventilation is usually suffient

decimonial,
If the situation is as you describe just tell the "other" guy he has no clue!
You have your answers above, if the activity is accurately described and truly out doors as per the other posts above then no issues.
Even if indoors as you describe at normal floor level with normal ventilation there would be no issues.

Gas welding seems a misused term now.
Typically it is Oxy-acetylene welding.
One supposes that in the construction site term it is mig or tig welding.
if the first, then more problems would be caused by having an actylene cylinder on-site.
If the latter then i would be interested/concerned about the area being welded in...enclosed or outside etc.
The other guy may well have no clue, but one supposes that he is in receipt of exactly which welding process is being used, the materials being welded and the area it is being welded in.
He also is in charge.
It is assumed that the material is mild steel.
It is presumed that the process is "gas" welding.

decimonial,
You need to get an accurate definition of the process, being old school, to me gas welding is oxy-acetylene.
Electric arc welding is what is more correctly known as manual metal arc (MMA), aka stick welding.
However, both MIG & TIG, metal arc and tungsten arc gas shielded welding are also electric arc processes.
There should be a minimal risk from the welding process itself if out of doors and the preparation done correctly for oxy-acetylene, bar for the fact that the products of combustion will rise and depending on the welders position these may enter the breathing zone.
Without full details of the material, position, and process it is really difficult to comment.
The gas shielded processes utilise an asphyxiating gas, though volumes are low and in a truly open space out doors if the welder is not in an area where these heavier than air gases can accumulate then there should be no issues.
You may find that keeping the shielding gas in place is more difficult!!!
You have the electric aspect, but again this is easy to manage, there should if done correctly be little risk of electrocution from the secondary side of the welding transformer.