Gas tungsten arc welding (GTAW), a widely used industrial process, is one of the most intense artificial sources of optical radiation. This paper presents a theoretical investigation of the UV (180-400nm), UVA (315-400nm) and blue light (300-700nm) radiation associated with the photobiological hazards to workers for argon GTAW arcs. The radiative properties of argon plasma were calculated and discussed for the three spectral regions of interest at temperatures from 5000-25,000K and atmospheric pressure. A two-dimensional model of a GTAW arc was then developed to determine the local emissions in the arc, the total radiation escaping from the arc and corresponding effective irradiances. This model is also used to study the influence of the welding parameters (current intensity and arc length) on the radiative properties and the effective irradiances. The permissible exposure durations for skin and eyes were further evaluated according to the radiation exposure standard of the Directive 2006/25/EC for the three spectral intervals. It is found that the UV radiation is most hazardous among these spectra. Indeed, it is shown that the UV permissible exposure duration is very short, e.g. from 5.89s to 9.8min at the distances from 0.5m to 5m for a typical GTAW arc (200A and 5mm arc length). This study clearly supports the importance of undertaking an effective protection strategy for workers, particularly for skin and eyes, in the welding environment.