Document 2R14j8eXJEdO07vkmLDJ8jp6N

8 35th National Safety Congress, 1947 Medial records of the individuals subjected io the exposure may be o( value if the examinations are thorough and frequent and not of a cursory type. .It must be remembered that occupational riivavn are slow io develop* mem and in some instances lasting in eflca.> Slow changes may not be detected and the mere fact that cases have not occurred is no definite assurance that exposures to known toxic materials may be ignored. The determination of the concentration of the toxic material in the air is important in evaluating the exposure. Tests of this type are not only indicative of the degree of con* Lamination but in some instances which op* eration is the major offender. The apparatus used in collecting the coo* taminant and the method used In estimating the amount present in the atmosphere vary with the type of material Tests of this type are specialized in nature and are beset with many pitfalls which on lead to very erroneous results and conclusions if dooe by other than experienced personnel. In a discussion pertaining to toxic ma terials it is gcrserally necessary to quote per* missible concentrations or as it is sometimes expressed -- maximum allowable eooceocralions--permissible limits, or threshold limits. These terms are used extensively by industrial * hygienists to indicate concentrations of a substance in the air which are considered compatible with good health. The limit usu ally applies to exposures of eight hours dura tion (or a prolonged period. The limits are. (or the most part, advisory standards or bench marks which are prac tical to meet. In general, thoe limits are de rived from three types of evidence ail of which have value and limitation*. i. Animals have been exposed.at different concentrations and the effects noted. a. A few experiments have been made on human subjects (or short periods of time. j. Safe limits have been arrived , at by measuring the concentrations of sub stance in the workroom air and corre lating this information with results of medical examinations of workmen. There is no magic connected with these liaiLs and the mere fact that they are ex ceeded does not necessarily mean that some one will definitely become ill, but there is a good probability that someone will suffer ill effects if the limit is greatly exceeded for a considerable period. There remains much to be learned regarding the toxidty of many substances used in industry, and it U hoped that with more rmearch and study that the answers will be found. So much lor the general picture. Now let's take a look at some specific operation*. Welding--Welding procases most common ly used an be divided into three type, arc. gas. and resistance. The safety measure per taining to dothing, goggles, and helmets are of common knowledge and therefore, shall not be considered in this disciwaioo. Are welding when performed on uocoaied steel doe not produce a condition which is considered harmful to the welder provided it is accomplished in a comparatively Urge open area. The fume which result from welding consist esendally of the oxides of Iron and oxide of metals which may comprise the steel or coating of the welding rod. Same In vestigators have found characteristic mark ings on chest x-rays of men who have welded under severs conditions for long periods of time. These markings are presumably due to the deposition of iron fume within the lungs, but it has not been demonstrated that such fumes have aused physical impairment. A frequently suggested limit tor welding fume is 15 milligrams of iron oxide per cubic meter of air. Concenualions of this magnitude existing in the workroom would, materially reduce visibility and thereby become a nui sance or an unsafe condition requiring cor rection. Welding within confined areas such as tanks, inside machinery or equipment, oc in small rooms presents a condition which can be of concern. The concentration of fume is materially higher under thoe cooditioos as there is little opportunity for dilution by natural air currents normally present in a taTge shop. Nitrogen oxida formed by the electric arc when inhaled in suftdent quan tities auses fluids to form in the lung--edema -with the resultant failure of the respiratory system. While welding in Urge open -.areas these toxic gases are normally not present in sufficient quantities to muse harmful effects. However, when welding is dooe in confined areas, the nitrogen oxida may rmeh a con centration which will be harmful. . Gas welding generally is not productive of harmful fumes. There are. however. In bal ing two potentially harmful exposures. While boric add or bonta generally an: used in