Thoriated Tungsten Electrode Hazards

Introduction
Thoriated tungsten electrode has low work function, stable welding performance and long service life, so in the early time it was widely used in welding industry.

Tungsten electrodes are used in tungsten inert gas (TIG) or plasma welding. During the welding process the electrode, arc and weld pool are protected from atmospheric contamination by an inert protective gas. A tungsten electrode is used in welding industry because it can withstand very high temperatures without melting or erosion. It is usually made by powder metallurgy and is formed to various sizes after sintering. Besides, according to different doped rare earth oxides, it can be divided into different types. Oxides used are primarily those of zirconium, thorium, lanthanum, yttrium or cerium, and doped quantity is usually 1%-4%. All these oxides greatly improve arc initiation, especially when direct current (DC) welding is employed.

Hazards
As we know thorium (Th) is slightly radioactive with a long half life and emits mainly alpha (α) particles, but occasionally some beta (β) and gamma (γ) radiation is emitted. Thoriated tungsten electrode was made by 2%thorium oxide, therefore, a low level radioactive material which contains in electrode, and it will cause small external radiation hazard and an internal hazard from ingestion or inhalation to welders. The external hazard estimated for a welder holding an electrode for a long time is a very small fraction of the maximum permissible radiation dose and it is concluded that the external radiation hazard is likely to be negligible. However, to achieve maximum arc stability the electrode tip should grind to a conical point before use and the shape is maintained during use by regular regrinding. During the grinding process, particles of electrodes may be produced with thoria on the surface. These dust particles that create the major hazard, as they may be inhaled. On the other hand, during welding, electrode will release hazardous substance, if welder ingestion or inhalation by accident it will harm to their health.

Storage
It is recommended that thoriated electrodes are stored in steel boxes with clearly labelled. When stored in closed boxes, there should no significant hazard in handling and storage. 10 pieces electrodes for one plastic box can be handled by welders safely without any special precautions.

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