Document a4DGEZb3NnQRQpwZ7EKDOz41b

Fume and Dust Exposure --From page 21 lo control the exposure. Medical rec ord* nf the individuals subjected tn the exposure may 1-e of va'ue if the examinations are thorough and fre quent nnd not of a cursory type. It must he remembered that occupa tional disease* arc slow in develop,incut and in some instances lasting in effect. Slow changes may not be detected, and the mere fact that cases have not occurred <i<>r* not mean that exposures to known tonic materials may he ignored. Drlrrminalion of the concentration of the toxic material in the air is im portant in evaluating the exposure. Teals of this type are indicative not only of the degree of contamination hut also, in some instances, which operation is the major offender. 'Hie apparatus used in collecting the contaminant nnd the method used iri estimating the amount present in the atmosphere vary with the type of material. Testa of this type are s|>ecinli/ed in nature nnd arc beset with many pitfalls which can lend to er roneous conclusions if done hv in experienced personnel: Permissible Limits In n discussion pertaining to toxic materials it is generally necessary to quote permissible concentrations, or as it is sometimes expressed--maxi mum allowable concentrations--per missible limits, or threshold limits. These terms are used extensively by industrial hygienists to indicate con centrations of a substance in the air which arc considered compatible with good health. The limit usually applies to exposures of eight hours duration for a prolonged period. The iimits are, for the most part, advisory standards or bench marks which are practical to meet. In gen eral, these limits are derived from three type* of evidence all of which have value and limitations. 1. Animals hsve been exposed si dif ferent concentrslions nnd the effects noted. 2. A few experiments hse been msde on Hnmxn subjects for short periods of time. 3. Safe limits have been smted at by measuring the concentrations of sub stance in the workroom air and eorrelating ihU information with results of medical exanninaticcs of workmen. The mere fact that these limits arc exceeded doej* not necessarily mean thiil someone wili l*ecome definitely ill. Ilut there is i good probability that someone will suffer ill offrets if the limit is greatly exceeded for a considerable period. There remains much to be learned regarding the toxicity of many *ul>*tanrrs used in industry. So much for the general picture. Now let's look at some specific opera tions. Walding Welding processes most commonly used can be divided into three type?, arc. gas. and resistance. The safety meaurcs pertaining to clothing, gog gles, and helmets are of common knowledge, and will not be considered here. Arc welding when performed on uncoated steel does not produce a condition considered harmful to the welder, provided it is done in n com paratively large open area. The fumes which result from welding consist es sentially of the oxides of iron and oxides of metals which may comprise the steel or coiling of the welding rod. Some inventigntors have found characteristic markings on chest x-rays of men who have welded under severe condition i for long periods of time. These markings are presumably due to the deposition of iron fumes within the lungs, but it has not l*en demonstrated that such fumes have caused physical impairment. A frequently suggested limit for welding fume in IS milligrams of iron oxide per cubic meter of air. Con centrations of this macnitude existing in the workroom would materially re duce visibility nnd thereby become n nuisance or an unsafe condition re quiring correction. Welding within confined areas such as tanka, inside machinerv or equip ment. or in amiff rooms presents a condition which can be .>f concern. The concentration of filin'- is materi ally higher under these conditions as there is little opj-ortunilv !or dilution by nntural air currents no: nally pres ent in a large slop. Nitn-ren oxides formed by the electric ai" when In haled in uufficieit quanf.k* causes fluids to form in the lenj --edema with resultant failure of the respira tory system. While welding in Urge open areas these toxic gases are nor mally not present in sufficient quan tities lo cause harmful effect. How ever. when welding is done in con fined areas, the nitrogen oxides may reach a concentration which will be harmful. Cos welding generally i- not pro ductive of harmful fumes. There are, however, in brazing two |*lcntiaQy harmful exposures. While l-oric acid or Iterates generally are used in braz ing fluxes, some metals require fluxes containing significant quantities of fluoride compounds and fumes hom these fluxes have been known to pro duce significant nasal irritatiou. Fluorides in general are looked upon with suspicion since they may pro duce haimful effects upon the bone structure. A limit of 2.5 mg. per cubic meter has been suggested for fluorides, but no standard has been agreed upon. Most industrial hygien ists Attempt to keep them as low u practicable. Silver solder is one of the more common alloys used in brazing. Sold ers of this type vary in composition and may in some instances contain cadmium which, if volaliliz<-d in suf ficient quantities, is considered harm ful. At present the suggested limit for cadmium fume in air is 1 milligram per 10 cubic meters of air. Resistance, spot, or butt \\elding of plain steel is of no concern from the physiclogical standpoint. -Tie fumes arising from such operations general ly are caused by the volatilized oil which has come upon the ra-iul stock during pir'ious operation* or has been placed upon the metal as a rust preventive. The preceding discussion of weld ing operations has been ba*cd upon the assumption that the met.ill being welded are of plain steel. The per formance of welding operations, ci ther arc, gas, or resistance, upon metals which have been coated with such toxic materials as lead, cadmi um, or mercury may cause harmful exposures. The heat of the flame or of the .arc causes volatilization of these metals. Welding or cutting of leme plate or other metals containing significant quantities of lead can Je suit in the volatilization of lrid fume, which if inhaled for a sufficient peri od of time, may rraujt in lead absorp- --To page 7i *2