Document vVX9qxmZ8yE9r0XwJK5ONzQZZ

26 Twenty-third Annual Safety Congress--National Safety Council tabling relatively lew larticlvs, make their way into the lympliatic system and accu mulate in tlte lymph nodes. In suflictent concentration, or jtertaps because they are mixed with >mall amounts of silica, tlicy set up a lmv grade, non-progrcssii-c chronic inflammation, liui this reaction results only in a little thickening in tlte lymph nodes and about the lymphatic vessels. The lung tissue may be variously pigmented, black iron* coal r red *rcn irwn, (nil there is no lonnaiton oi scar (i.uuc that interiervs with iunctiun. Tle susceptibility to lulnrrculusis ot the i>ersun with such pig mentation is nut increased but it is apparently guile definite that pneumonia is unduly prevalent in coal miners ajtd tliat chronic bronchitis results from the itihalathui of cement. Tle X-ray films of men working in noil-siliceous dusts shows either nothing at all or a more or less marked accentuation of the linear shadows cast by the blood vessels. This, of course, is due to tl*c chronic inflammatory clianges about the |ymphatic trunks in walls of blood vessels. The effects oi mixtures of free silica and non-siHccous materials are less clearly defined and should receive more serious attention. It would seem unwise to assume, as has been done in the |iast, tliat the non-siliccous substances serve only as inert diluents and that only tlc quartz coin|oncnt oi a dust is oi significance. Expertmental and cliuical data arc accumulating which stages! fliai at least some olJier dusts may materially modify the action of guartz. both in its cajcicity to produce nodular fibriisU in the lungs and to increase the susceptibility to tuberculosis. For example, animals^ inlialing heavy concentrations of a mixture of equal parts oi jwre silica and Iwmatilc dust tor eight hours a <lay over a jktwkJ of 14 months liavc >hown not even the slightest indication of nodule iormation in the lung, whereas pure quartz dust, inhaled for only two hours a day. prHhicc$ definite nodulation. It u1m> seems to be true tliat animals inhaling such a mixture arc much less susceptible to iuliercu|o$t$ than those exposed to pure quartz. In the case of the human iron miner, some luugs show definite silicotic nodulatiun. other* only a very few nodules and many no nodules at all. All exhibit hcavv dejfosits oi iron particles with a cellular connective tissue reaction. When these findings can lie correlated with chemical analysis of the lung^ tissues and the approximate amount of rock work which these miners liavc i*erformcil. some relationship between the exposure to silica and the fibrous nodule formation may lc established. Tulicrculosis in these iron miner* is apparently less iirovnlciit ami much less severe than in men exposed to pure silica. What lias hem said oi iron miners is also prnliahly true of foundry workers and coal miners. It is generally accepted that men in the* latter nccupatum liavc less tuberculosis tlian the average tor the age i*criod: Cummins liclicvcs tliat they liave tlie iniection Imt tint it is so atypical and benign in its manifestations tliat ft escapes diagnosis. Mention should also lie made of mixed dusts like certain slates ami granite containing large amounts of free silica in combination with silicates. Experimentally these substances behave atypically and do not produce nodular fibrosis unless there is complicating iniection. Tlte same may also he true in human licings. Unques tionably such dusts arc callable oi producing typical silicotic nodules and they predispose to tuberculosis. From a theoretical standpoint thev should receive much tmire intensive study to clarify our views on the whole subject. At tlte present time it appears that the action of their quartz component is modified and partiallr neu tralized by the other suVtarices which they contain. Using Exhaust Systems and Respiratory Equipment To Protect Workers Exposed to Dust By STUART W. GURNEY and DAVID S. BEYER Liberty Mutual Insurance Company, Boston , Ti*c speaker said in part: A number of our states have liad references to dust elimination in their labor laws for a good many years, but no state lias as yet thoroughly enforced those laws. The codes of "five states which we investigated provide tliat grinding, buflitig and polishing wheels should !>e exhausted. although two of the stales exempt from these provisions wliccls on which water is used. Dust in Industry 27 This seems ill-advised, since a study of wet and dry grinding in Connecticut by Winslow and Greenburg lias shown that tlc application of water does not by any means eliminate the dust Itazard. It may be remarked that, with everything else equal, a high static suction will give a higher velocity at the point of origin of the dust, fume or gas tlian a low one; but this alone is not a measure of the effectiveness of any exhaust system. Wisconsin has adopted tlte principle of specifying a limit to tlte numlicr of dust particles of respirable size per cubic foot of air. After all. this is wlial we are primarily interested in, to keep the dust contamination down to a point where it will not be harmful. These variations and conflicting provisions in state codes merely reflect tlie gen eral lack of authoritative standards. It is accordingly fortunate that definite steps arc now (icing taken bv the American Standards Association to develop the proper basia for such codes. * There arc two committees working on this problem; the Ventilation Code Committee, sponsored by the American Society of Heating & Ven tilating Engineers, and the Exliaust Code Committee. sjKmsorcd by the Inter national Association of Industrial Accident Boards and Commissions. It is also arranged to appoint sub-committees to take up five specific subjects: Abrasive cleaning, chromium plating, granite cutting, rock drilling, and spray coating. If addition, a Sub-Committee on Fundamental Principles of Design and Operation and Maintenance of Exhaust Systems will be appointed. The two most important considerations in an effective exhaust system are: I. Velocity of air flow: 2. Arrangement of the inlets (from the standpoint of near ness to tfie dust source, stiape, etc.). Many an installation that is otherwise all right fails to remove the dust success fully merely because there is not enough air being drawn through the system. In a series oftcsls tliat were conducted under actual working conditions by Theodore F. Hatch, Department of Industrial Hygiene, Harvard School of Public Health, a machine used in dressing stone was employed, and it was noted tliat with an air flow through tlie hood of 230 cubic feet per minute, there were over one hundred million dust particles in the surrounding air. When the air flow was increased to a little over 250 cubic feet |icr minute, the dust concentration tad drnpjicd to forty million, a marked improvement. As tlie air flow was further increased, the drop in dust concentration was relatively slower, ami it took a volume of alxmt 380 cubic feet per minute to firing the dust concentration down to leu or fifteen million particles per cubic foot, which was considered reasonably safe ior this tvjic of dust. It is accordingly possible sometimes to take an installation tliat is not satis factory ami. if the* remainder of tlie system is well designed, by merely speeding tip the blower or adding a larger one. to bring abont the desired results. Another very inqxirtant consideration is to get the inlets of the exliaust system as close as possible to tlie source of the dust. Tlie drop in efficiency as we gel further nwav from the inlet is really surprising to one who lias not studied the prin ciples involved. It should be remembered tliat if we have the open end of an ex haust pipe or air duct in operation, the air tcmls to flow in from all sides, even from behind the opening. As we move away from the end of the pipe, the velocity drops very rapidly, so that even at a distance of five inches from the hood the velocity may he less than 10 per cent of tliat right at tlie hood inlet. This is the most important consideration to keep in mind and one which is frequently lost sight of in designing exhaust systems. It is not uncommon to see an exhaust inlet a few inche* in diameter with which the person making the installation Imped to drawdust from a distance of several feet, hut the air flow even a foot or two away from the entrance to the inlet may lie negligible. Still another important consideration having to-do with the design of the inlet is the addition of a flange. The effect of this flange is to cut down the air that would flow in from behind the opening, thus drawing it nearly all from the front. Thus the efficiency of the system is snlistantiallv increased and tlie scope of the ex haust extended appreciably.* without increasing tlie power consumption or otherwise adding to the expense of keeping up tlie system. There arc also other considerations of perhaps lesser importance. For example, air cannot he "pulled** from a distance by mcrclv directing an exhaust pipe toward the point in question, but it can be "pushed" or Mown, directionally, for a consider-