These colors are evidence that visible light is being radiated. Exposure to those chemicals can cause damage to health. Welding fumes rarely if ever contain just one contaminant. It is difficult to determine just what kind of exposure a welder is receiving during any particular operation. Toxic chemicals may result from the metal being welded, the coating on that metal, the contents of the rod including the fluxes, the products of incomplete combustion, or ozone and nitrogen dioxide.
Nitrogen dioxide is developed in both electric arc and torch welding.
In arc welding the amount of nitrogen dioxide produced depends primarily on the length of the arc, the voltage, and the amperage. Nitrogen dioxide is a particular problem in automatic welding where a heavy electrode and high amperages are used. Nitrogen dioxide is an irritant that penetrates deeply into the lungs and slowly attacks the tissues. It may do extensive damage before the first symptoms appear, often many hours after exposure. Ozone is most commonly present in electric are welding and in the of aluminum and stainless steel.