Document nNyeKEMvBNLv9pqNMgNgQJnVX

Welding and Cutting or not the base metal is coated with such materials as tar, paint, lead, or zinc Cases -- the oxides of nitrogen, carbon monoxide, ozone--and metallic dusts and fumes may, in varying degrees, present inhalation hazards if adequate respiratory protection is not pro vided ASI Standard Z49 1, Safety in Welding and Cutting, gives specifications for local exhaust systems, general ventilation, and health pro tection of workers on vanous types of weld ing and cutting The following discussion is based on this standard, which should be con sulted for further information In open-air welding or cutting or in large, well-ventilated areas, where clean carbon steel is welded or cut .with bare or coated carbon-steel electrodes and without inertgas shielding, minimum health hazards exist In confined areas, such as tanks, pressure vessels, and holds of ships, local exhaust or general ventilation systems should be pro vided to maintain concentrations of toxic gases, fumes, or dusts below maximum allow able concentrations (MAC) as defined m ASI Standard Z37 Senes "Allowable Concentra tions of Toxic Dust and Gases," or below threshold limit values (TLV) specified bv the Amencan Conference of Governmental Industnal Hygienists For a complete dis cussion, see Chapters 41 and 42, "Industrial Hygiene" and "Elements of Industrial Toxicology " If gases, dusts, and fumes cannot be kept below the MAC or TLV because work is inter mittent or for other reasons, welders should wear respiratory protective equipment ap proved for the exposure by the U S Bureau of Mines Where oxygen is also deficient, self-contained breathing apparatus or hose masks with blowers are necessary Coatings, fluxes, and base metals When welding or cutting involves coatings or fluxes containing base metals that contain elements such as zinc, flourine, beryllium, lead, or cadmium, and their compounds, local ex haust removal or general ventilation should be provided to maintain the concentration of any toxic fume generated below the MAC or TLV Outdoor welding and cutting involving lead, mercury, and cadmium require that the worker wear respiratory protective equip ment Fic 31-H -- Local exhaust for gas welding Courtesy Automatic Electric Co Generation of gases and fumes Oxides of nitrogen from the high-temperature combina tion of nitrogen and oxygen in the air are al ways generated near the welding or cutting arc An inert gas shield, however, minimizes the introduction of air to the arc Concentra tions of these oxides are generally above their MAC or TLV within a few inches of the arc, but are diluted rapidly by air movements Local exhaust or general ventilation should be used to keep the concentrations of oxides of nitrogen within safe limits Ozone --a triatomic form of gaseous oxygen, chemically designated by the symbol Ot -- is formed bv ultraviolet radiation acting on oxy gen in air It is a highlv toxic and irritating gas Since ultraviolet radiation passes through the air, ozone mav be formed several feet from the welding or cutting arc The amount of ozone formed depends on the metal and the gas shield being used and the arc temperature A greater amount of ultraviolet is produced with argon gas shield than with helium General ventilation will usually 942