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.
At high levels it may cause fluid build up in the lungs. The immediate effects of ozone are dryness in the mouth and throat, headaches, and difficulty in breathing. Flourides are among the many contaminants to the respiratory system that come from rod coatings. Fluorides are released in large amounts during the welding of stainless steel and during brazing and soldering. They can cause mild to serve irritation to the upper respiratory tract.