Welding on farms is important to maintain, repair, and modify equipment, machinery, and facilities. Welding involves melting, fusion, and bonding of similar metals. Welding activities take place periodically, often in field-expedient conditions, with variable frequency and duration, and under time pressure. Since welding may not be a primary activity on farms, farmers may be inexperienced or out of practice, which might contribute to exposure or unsafe work practices. A variety of metals are used in or on farm structures, facilities, and equipment such as aluminum, mild steel, hardened tool steel, and stainless steel. Structures, facilities, and equipment painted or coated for corrosion resistance often need repairs by welding. Surfaces and materials that need repairs by welding may be dirty and grease coated, often requiring flammable or toxic solvents like trichloroethylene to clean the surface. Paints, coatings, and cleaning agents used to prepare surfaces for welding can react or produce hazardous air contaminants. Examples include lead-based paint, coated galvanized steel, and reactions from metals treated with phosphates. There are various types of welding. Welding fuses metal parts together under heat by electrical arcs or high-temperature flames. Electric arc welding uses consumable electrodes with or without shielding gases supplied from compressed gas cylinders and nonconsumable electrodes with shielding gases. Welding can also use intense heat from the combustion of acetylene or other fuel gases or the creation of hot plasma to weld or cut metals. Dissimilar metals are joined by brazing and soldering. Welding is just one of the many potential exposures to farmers and agricultural workers that alone or in combination may affect their health.