Document LKpV8OVLqQgn7kmnVe65O3Dod

WELDING AND CUTTING Personal Protection Respiratory protection During welding and cutting operations, tone gases, fumes, and dusts may be evolved, depending on the typo of electrode used, the base metal being welded or cut, and whether or not the base metal is coated with such materials as tar, paint, lead, or zinc Gases--the oxides of nitrogen, carbon monoxide, ozone--and metallic dusts and fumes may, in varying degree, present in halation hazards if adequate respiratory protecbon is not provided American Standard Z49 1, Safety in Weld ing and Cutting, gives specifications for local exhaust systems, general ventilation, and health protection of workers on various types of welding and cutting The following discussion is based on this standard, which should be consulted for further informa tion. In open-air welding or cutting or in large, well-ventilated areas, where dean carbon steel is welded or cut with bare or coated carbon-steel electrodes and without inertgas shidding, no health hazard exists 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 al lowable concentrations (MAC) as defined m American Standard Z37 or below thresh old limit values (TLV) specified by the American Conference of Governmental In dustrial Hygienists If gases, dusts, and fumes cannot be kept below the MAC or TLV because work is intermittent or for other reasons, welders should wear respira tory protective equipment approved for the exposure by the U S Bureau of Mines Where oxygen is also deficient, self-con tained 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, flounne, beryllium, lead, or cadmium, and then compounds, local exhaust removal or general ventilation should be provided to maintain the concen tration of any toxic gases generated below the MAG or TLV. Outdoor welding and cutting involving lead, mercury, and cad mium require that the worker wear re spiratory protective equipment Generation of gases and fumes Oxides of nitrogen from the high-temperature com bination of nitrogen and oxygen in the air are always generated near the welding or cutting arc An inert gas shield, however, minimizes the introduction of air to the arc. Concentrations of these oxides are general ly 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 con centrations of oxides of nitrogen within safe limits Ozone--a tnatomic form of gaseous oxy gen, chemically designated by the symbol Or--Is formed by ultraviolet radiation act ing on oxygen m air. It is a highly toxic and irritating gas Since ultraviolet radia tion passes through the air, ozone may be formed several feet from the welding or cut ting arc. The amount of ozone formed de pends on the metal and the gas shield being used and the arc temperature A greater amount of ultraviolet is produced with ar gon gas shield than with helium General ventilation will control the production of ozone in the welding or cutting area. Ultraviolet radiation from the welding or cutting arc can also decompose chlorinated hydrocarbons, such as trichloroethylene and perchloroethylene, to form highly toxic sub stances. Since this decomposition can occur even at a considerable distance from the arc, degreasing operations and other work using these chlorinated solvents should be located so that no solvent vapor will reach the welding or cutting area Inert-gas shielded arc welding requires that much greater precaution be taken to provide respiratory protecbon than is ordi narily the case with other welding or cut ting processes Depending upon a number of factors, including the particular variety of gas-shielded arc welding to he done, the nature of the materials to be welded, and whether or not the work must be done in a confined space, there will be a need for pro vision of positive ventilation, local exhaust removal, or approved respiratory equip ment, or a combination of them Indoor exhaust and ventilation In spaces of 50,000 cu ft and over, where welding is an essential part of the work, local exhaust 29-24