If you are a professional welder you may know how dangerous welding is and it is recognized as one of the most dangerous jobs all around the world. While welding, sparks, spatter, flame, etc. are always spreading around it.
Apart from these the most dangerous thing is the emission of Ultra-Violet (UV) & Infrared (IR) radiation. These rays are so harmful to you especially for your eyes & you know eyes are very important for a human for any kind of task.