There is no clearly defined limit since the distance depends upon the exposure time, welding process, welding current and other environmental conditions. The US Army have carried out trials which propose distances of between 3 and 20 metres for an exposure time of 10 minutes for MMA (SMA), MAG (GMA) and FCAW in order for UV exposure to be below the US daily threshold limit value.
Other sources, however, state that all radiation from a welding arc is potentially hazardous and there is therefore no safe limit. At present the best advice is to screen off the area in which welding is taking place in order to protect completely workers or members of the public not equipped with adequate eye protection from the effects of the welding arc.