Document rB6KaQN797KM61yrLvvynOvVa

10 3Slh Notional Safely Congress, 1947 grinding of noiuoxic metals which are free of sand is generally considered a nuisance and is not harmful per sc. Despite this fact some state Ians require griding operation' to be ventilated. This requirement has probably been a hold over from the days when sand* Mone wheels were prevalent and also to prevent the creition of a nuisance condition. Grinding wheels in use in industry have ar tificial abrasives such as aluminum oxide or silicon carbide. Emery, which is a natural product composed of osemially aluminum and the magnetic oxide of iron, may also be used. A permissible limit of 50 million par ticles per cubic foot of air for aluminum oxide and silicon carbide was recently ac cepted by the members of the American Con ference of Governmental Industrial Hygien ists. Such a limit is liberal and concentrations of such magnitude are normally not en countered. When lead, silica, or some similar toxic material comes in contact with the grinding wheel the exposure to the abrasive matter may be ignored and the exposure evaluated on the basis of the toxic material. If this Utter material i controlled the nuisance will also be eliminated. VentiUtion systems for grinding wheels have been fairly well standardised and gen erally are satisfactory to present a nuisance. Hoods should enclose (he wheel as completely as is practiable. Air volumes should be pro vided which are sufficient to cause an inward flow into the hood when using the smallest wheel. This is especially true where toxic materials are involved. Wet Grinding-- Baffles, hoods, and guards are generally located near wet grinding wheels to prevent dispersion of (he liquid used as a coolant. These devices are usually sufficient to control the dust if it is nomoxic in nature. If the dust liberated is toxic, me chanical exhaust ventilation may be required. Buying and polishing--The buffing com pound applied to wheels used ' for buffing and polishing vary in comijodtion. Waxes and various types of abrasive are the major components. These materials plus Hut and fibers from the wheel are the essential in gredients of the airborne dust. The toxicity dependent upon the type of abrasive. Generally ventilation is provided 10 as to improve housekeeping and reduoe the num ber of complaints and not because of the hazard to health. . Machining--Smoke from oily parts is the prevailing source of air contamination at machining operations, lllncst has rux been attributed to this type of exposure. As is the case with roost fumes and dusts of the nui sance variety little is known as to what ef fect such materials have on already existing physical abnormalities. Machining operations on steel produce large chips or turnings; consequently, duu is not a problem. Operations involving the machining of high lead alloys hate been studied, and significant quantities of air. borne lead have not been demonstrated. Graphite which becomes airborne during the machining of cast iron is oot considered to be phvuologirally significant, anti there fore is classified as a nuisance dust. Frequent ly management considers it advisable to pro vide ventilation for tbc machines which are productive of the most dust, as graphite on the clothing and person and surrounding machinery is conducive to many complaints. Ventilation systems for the machining, drill ing. and so forth, of cast iron should in clude hoods located as near the cutters or drills as is practicable. Many of thee hoods are in use on production machinery and are doing an excellent job.of dial control. Abrasive Cleaning--Since silica is recog nized as the most harmful of mineral dusu. an adequate ventilation system is normally provided at the time of installation of com mercially built sand blast equipment. Con tinuous usage and lack of maintenance result in a breakdown of adequate control. Visible escape of dust is the belt evidence that this has occurred and it is advisable to correct such a condition without undue delay. Employees who are stationed in blast rooms are dependent upon personal respiratory equipment. It is of utmost importance that such devics are of a type which will preside the necessary protection. Devices of this type arc of the supplied-air variety, and it is neces sary that the air provided be free of harmful contaminants. The air compressor* should be located in an area free of contamination otherwise the contaminant will be transmitted to the helmet and the breathing tone of the worker. * Normally, ventilation within the room is provided so as to improve visibility and to help prevent the escape of dust to the surrounding areas not to reduce the oncentration of silia dust to a safe level.