Document 9JO6XE9JJZ7BVYBx221GpeY9p

COKTSOL OF JLoT PF.GSLSL3 Hi LidsTKI T,.J. l/.cConnell, ii.D. Assistant i*ealcal director Director, Inaustrial heaxtb Bureau The extant 01' duet control required x'or any particular plant area is I determined by the predominating action of the contaminating dust or nixturea ox' dust on tiie body ana the severity of uust exposure. The size ox' tue partioxes of dust resulting from tue break aoen or disintegrationi of solid materials through physical or aecnanical means range from particles risible V. tne c/e aoen to microscopic ana sub-microsoopic aimensions. Very often it is tue Invisible dust that causae tne most bars. Tne particulate mattor of I'ani and smoke created by processes such as burning, sublimation, and the reaction of gases to x'orn solids is usually lass than one micron is size. The concentration of oust partidos dispersed zithin the breathing zone ox .orkers is determined wherever possible ty standard air sampling procedures, since not all methods are equally trustworthy. The better trained the industrial engineer or enemlst the more reliable the results. The analyses ox' samples vary depending upon tne nature ox' the materials and the information desired. The fibrosis-producing dusts, for example, are determined by a prescribed technique and expressed as number, size, and composition In a unit quantity of air. In some special instances tue amount of dust is determined gravimetricaliy. Quantities of most of tne other air-borne dusts are generally expressed on a weight-volume basis. Where indicated, chemical and spectrographic methods ox' analyses are used. Hr contaminants usually ester the body through the respiratory tract. Ingestion and absorption through the skin are less important portals. h - *- Hot all dusts in concontritions nm> i '<y ancountereo in inoustry ore naruful. lose are physiologically inert ana lie ire#, others nay be encap sulated in the tissues, or nay be absorbed without ;.rouucing ar.7 noticeable effects, lusts, sued as carbon ana iron oxiue, are believeu to retara toe onset ana moaify the progress of silicosis. Limestone &na cardie are examples of ousts enich cause no injurious effects. Hovever, harmless dusts in high concen trations aay be of a nuiaanoe nature ana mivih be Icept to a ninisun. Of the harmful variety of dusts some exert their effects locally on the sain, nucous membranes, conjunctiva, teeth, ana through irritation to the upper respiratory passages, fany organic dusts produce allergic reactions in sensitixeo persons with resulting asthaa, rhinitis, and other aisturbenees. In im portant group of dusts vhlch are insoluble or only soluble with oilficulty in tiie ben^ fluids initiate fibrous enanges is the lung tissues. These are United, so for as as hare evidence, to a fe* of the inorganic itInoral dusts, such as silica and asbestos. In equally inportent group of dusts ihich are soluble or slightly soluble is the body fluids ure inherently toxic vnon inhalod, ingeatoa, or otoeraise absorbed. Lead, aanganese, areenle and tuolr compounds are example*. Incxuued among the dusts of this group are those cnicb may be irritant as ceil as toxic, as for axaaple the explosive 1ST trlnltrophsnol, and picric add. A fifth group of ousts causing increasing concern are tboae arising from radio active ores. The diagnosis of any barnful effects to tne worker induced by exposure to dusts is entirely u medical problem and. is based upon a correlation of the ,,ati ent' a occupation, symptoms, and physical finoings. laboratory end 2-ray examinations must be Included rhen indicated. The periodic health examination offers to* most effective mans of discovering early not only tho occupational -3- ci.SM.898 or Intoxication^ but also serves to check toe adequacy oi' preventive neaaurea designea to prevent harmful substanoes from escaping into too breathing zone of eorkers* It is important for tno uhysicien to familiarize r.lmseif rith every plant process sou rtth the materials used in tua plant so tnat he oay ap praise tbe vorisers' surroundings* A basic consideration In formulating a program of dust control must meet operational requirements as veil as provide protection for tue maximum number of corkers. The first thought in prevention should, be given to the possibility of subotituting harmless or leas harmful substances for harmful ones woere tnere *111 be no interference vitb t.e quality of tuo ^roouct. Typical instances of suc cessful substitution include the adoption of nonsiilceous parting compounds is foundry practice* of steel shot or grit in place of sand in blast-cleaning operations* and of artificial abrasive grinding and polishing vheels for sand stone thesis. There substitution is not practical various engineering notxiods may be used. It is* of course* preferable for plant management to consult toe engineer before the plant is built or remodeled so that control features can be engineered into t a plant ana machinery* Some machine manufacturers aov include control equip* L.ont as as integral part of machines Imom to produce or disperse duets. Operational changes or a change in the proceed to eliminate specific hazardous aspects should be considered. Conversion of *:and operations to partial or full mechanisation may be possible* fceebanleal handling and remote oontrol of dust-creating operations frequently permit the use of more complete enclosure and ventilation application as veil as toe removal of the worker from zones of highest duBt concentrations. Solaoring processes may sometimes be coangea to welding* thus eliminating lend fuses end dust. -4- Segregation of dusty processes may be used to advantage. '`here ^iant layout and operational procedure la designed to ceroit separate housing or isolated locations x'or dust-proaucing operations, particularly loose uifficuat to conxrol, the exposure is United to the least muxbar of vorkers. This con sometime* be accomplished by arranging toe working or production schedules to permit postponeacnt of highly dusty processes until tbs ena oi tUs shift or i-rlncipal work ing period, this latter procedure Is commonly used in tae case of rocxhlasting operations, ehsiceout ana sana-conaitioning v.ork in founary ..ructice. This lias toe advantage of olther simplifying required ventilation measures or Halting need for personal respiratory equipment as tell as of reducing the exposed number of workers* The enclosure or total encasement of dust-proaucing units, such as convoyor halts, screes ana elevators, vibrating screens, grinding mills anu bagging machines, is effective in greatly reducing dust dispersions. Thr application of mechanical exhaust to the enclosures till further aeerease tue escape of dust from these sources* It is sonetlaes possible to abate Oust dispersions sufficiently by vet aethods, such as spray or stresa of aster or by tue use of foams, colloids and othar vetting agents* Their value, hovever, ia limited and should always be checked by dust counts in the adjacent breathing zones* The most preferred single method of controlling dust diujmrsions is by effective ventilation* by effective, I mean a ventilation system that is designed to conform with established engineering principles and recognized ood practice. It follows, also, that aaoquate care should be observed in its use and maintenance. The basic criterion in the design of ventilation meosurus or mechanical exhaust systems is the production of air currents at the point of oust generation at a rate vuich will oestroy tno energy of tuo escaring oust anu fsroe it into 5 w.<i .oisiuut systea, thereby reduoicg dust concentrations to aitiiln uufo Units, j.n officiant aaiuust s/ates produces uuoquste udr velocities nitn .-.injuuia powr consuaptlon in tnc _rou cf nut , rouuction uu u i_iniaum uir ilo* iron the dust free uraee. ad coiuujt ayirtes snould bo equip, ea sit:: u suitable nood to eno*ose -s aich ns ..ossibia the sources of Just promotion and to ,rovlda uir velocities sufficient to aruv too particle* Into the exhaust systea. Uxuesa it Is pructicsbio to uis-osa oi Uio 'j-^t isto tiio outside utsospiure, the aystan should also to j..uip..oa Mti. i. dust collector or ~.cins of flltr-tion. "lore t;.o cutoido uto.o&. bare is asod .'or disposal, . nac-oitlonary oouour.'s should ue tns-n to ; revet:t .a-.iiuo recirculation or re-entry of t.a -otu.Miinataa --r t-u-ot^ o. co sinuous cr otiler uuuns oi' access. Obviously, teonnical engineering knouieuga *nu ox. erionco are sosentic* to assign sa oasaust systec that till adequately control or eliminate lust cisporaiooe of oporatiuia producing dust* Good ,;onsrua. ventilation or dilution ventilation of t.orxang -,.-Cs is often -Ui.latent if too rate of dust production is not oxcesuivo. - aero id^ii voluues .* -ti- -ro e&.loyed euro uUat be tuxes to -Vuiu unaeeirablu uruz'ts. General vontia-tion oy aecnunicol sxbuust neesurjs similarly rcquiroa careful tuoy c. tus . roolea la order tc bo ful-y effective* .Tincdpel f-ctora include Adequate -ir uovaoent at tno p-oints of highest dust concentrations ana juiuoa air flos to the sources of sxbuuot* Short circuiting of uir flex is a coaaoo failing in this -stood of control. 7entilutioo neasuros ana exhaust systems, hoxever efficient then first .nstailed, are apt to deteriorate or be misused. All such equipment requires con stant checking uno maintenance* It is not uncommon to fine expensive installations of oust control ocuipoent ranoaren tore or less useless by cecuunicol u*fects or uy mishandling on toe yurt oi' tu vorxora. The efficiency or dust oxnuust systems -6- ana other methoas of forced ventilation snouid oe checjtoa ly neons oi _ir samples t-sen by on roved teeunique. This sboulu be aone men t.*c system is first installed ana -erioaically thereafter. 'ono^r particular circumstances respirators ana otner respiratory protective equipment v.orn by the inaiviuual worker may provide sufficient protection egainst busts. The simplest type is toe mecnanical-filter respirator rhich removes a varying amount of a particulate contaminant from thu air .massing through it. The better the filter material tho nigner the ..ercentage of oust removed. Only filters v -.proved by trie to>. ouroau of mines for different Ainas ex' uustb buoulu be used. They are lnt9naeu for exposures of short duration ana not for continuous use. The supplied-uir respirator Kith helmet is used xsrgely in operations mere t..o particles cay injure tne face and eyes, such as ssnobiasting anu metal grinding. If is essential that this ty^c of respirator oe .roviaed vitii an adequate air supply uravn from a ;.ure, -ust-free source. Theuistoos 1. sometimes male of taming the air airoctly from a compressed air line without providing the air intajvs to uoupressors ?.ith a filter capable of removing tee fine oust particles. . ernaps tne air of tuc compressea air line nay be *et ana oily giving rise to ouors <aa even in instances aaero hot compressors partially aeccmpose the oil to carbon monoxide gas anu other gases, naturally, uaaer tnese conditions, the -ir is unsuited for use in th* respirator. It then becomes neeessary to install a snail rotary cou.ressor or bloeer vita a clean source of air. This latter -ethod is also applicable in plants not equipped vith compressea air. Unfor tunately, then renters are ongtgea 1in operations requiring freeaom to move about unhampered by air hose, toiu type of respirator cannot be torn. The effectiveness of personal protective equipment, inexuuing respirators, gloves, and special clothing, depends upon proi>er selection _cq maintenance. The education of the toneer in their correct use is iisevise important. - 7- ana cleanliness, so far a* practical for tao type cf work car ried on, cr.- important factors in oust control. For clsanin;, safety, and effici ency, floors should be of concrete, wooden blocas, granite, or other impervious raterial. There wet processes are used, adequate drainage should be maintained, ana dusk boarding on other dr7 surfaces on wnich workers con stand should be provided. In tne event this is not practical, rubber boots Should be furnished, nails, overhead structures, ona equipment should be cleaned periodically, perfefably by means of a good vacuum ayatern. Whan possible, sleeping ana denning snoiua be done aftr woricing hours with ample protection afforded 'those so engaged. All waste products should be disposed of In a safe manner as often as neeees-ry. I'nuer management supervision a responsible person or porsuns should be assigned the taaK of supervising housekeeping conditions. Elimination of bad shop practices is best accomplished fay instructing workers regarding augers incident to occupations. The employee too understands the reason for employing rrotsctive methods unu devices mill in most instances cooperate tith management in obtaining results. These general principles of dust control measures together with adequate -edied supervision of toe worxer are cur best solution to the control of the uust problems today. THE HELICAL SOTECTISIPW n? ffonraws r.TPf>ssp TO DUST BT T. J. UcCOSBELL, HD. ASSISTANT MEDICAL DIRECTOR IS CHARE 07 IHOTSTHLAL HEALTH SECTION TCUAF2 DIVISION 1STRQP0LITA2J LITE INSURANCE COMPACT Sts' THE MEDICAL SU72B7ISI0W 0? 70mT5 EXPOSED TO PtTSJ* *7 W. J. UcCoaaell, M.B. The hazard resulting from certain dnaty proceeees in industry, al ways on important problem of industrial medicine, has been given undue publicity within recent years, end the conflicting testimony of those who specialize is the litigation field has led many industrialists to consider claims of alleged disease resulting from dust exposure among the common rackets of the day. Al though many of these claims are admittedly vague and appear to be based more upon the universal desire to get something for nothing than actual injury, health impairment often follows exposure, usually after a period of years, to certain dusts or mixtures of dusts encountered in industry. The harmfulnass of dusts varies widely in accordance with the physical and chemical natures of each individual substance. Certain duets are soluble or slightly soluble in the body fluids and their harmful effects are proportional to the tordcity of the conpounds formed. Lead, mercury, and arsenic are exasplee of poisonous dusts,.- Other dusts exert their harmful effects locally on the skin and mucous membranes and through irritation to the respiratory passages. Chromic acid and*alkalies are exasples. Attention recently has been called to the probably harmful effect of dusts arising from radio-active ores. A fourth group of dusts which are insoluble or very diffi cultly soluble in the body fluids may Initiate harmful pathological lung condltlons. These aay be subdivided into non-flbresls and fibrosis producing dusts. Presented before Twenty-Third Annual Safety Congress, National Safety' council, ' Cleveland, Ohio, October 5, 1934T -2- (By fibrosis Is merely meant the replacement of the normal elastic lung tissue by an unyielding sear tissue.) The organic dusts, mainly the vegetable fibers, such as cotton, Jute, hemp, etc., are non-fibrosis producing dusts. The fi brosis producing dusts are limited, so far as we have evidence, to a few of the inorganic mineral dusts, such as free silica, crystalline silicon, quartz, as certain combined silicates. Of the fibrosis producing dusts, those having a high percentage of free silica are admittedly the most important because ex posure over a period of years to such dusts distinctly predisposes the individ ual to tuberculosis. It is seldom, however, that any one of these groups of dusts occurs singly in industry. Usually we are confronted with a variety of dusts in vary ing combinations, and until research investigation determines the effects of mixed dusts in measured combinations, it is difficult, if not impossible, to evaluate their degrees of harmfulness. The diagnosis of a disease induced by exposure to dust is entirely a medical problem, and is based upon a correlation of the patient's occupation, his symptoms, and physical examination. Laboratory and X-ray examinations must be included when indicated. The elimination or control of a dust hazard re quires the assistance of the engineer, the chemist, and specialists in other sciences whose training enables them to contribute additional Information. It is essential to determine the source of origin of the harmful dust, its concen tration within the breathing zone of workers, its chemical composition, and in most instances, the particle size measurements of the dust. With this informa tion and a knowledge of the length of exposure, taking into consideration indi vidual susceptibility and other physical defects of certain individuals which may favor the action of dusts on or in the body, the extent of the dust hazard -3- can "be fairly veil estimated.. Dust determinations indicate the locations where preventive measures must he applied. The effective method of prevention depends upon the circum stances giving rise to the hazard and may include the segregation of the dustproducing operations i the hooding or enclosing of the operations with the appli cation of adequate exhaust ventilation, increased general ventilation, the use of protective clothing end respirators, good housekeeping, and, most important of all perhaps, the consistent maintenance of dust control equipment. The methods hy which dust aay he collected and studied as to its chemical content, size of particles and amount per unit volume of air, have been the cause of much investigation and research. The general procedures followed have been so ably described by previous speakers before this group that any re ference I may make would merely be a repetition and a digression from the sub ject of the paper. The effeetivnass of dust control measures in preventing diseases produced by dusts can be detezoined only hy careful physical examination of the workers so exposed under the guidance of conpetent medical supervision. The benefits which accrue to the employer end employee, alike, as a result of the physical examination of all applicants for enployment, as well as periodical examinations of those already engaged, would indicate very careful consideration by industry of a program for control of sickness. Such a procedure protects the employer from engaging an applicant already physically or mentally impaired who later may claim disability for a condition either not associated with employ ment or contracted during a previous enployment. The applicant's physical and mental condition is established and by keeping recorda of his subsequent ill nesses and accidents, the question of responsibility for injuries and sidnesBes incurred during employment need never arise. She applicant is protected from engaging in work for which he is physically ill adapted which, if undertaken, might easily bring about serious impairment of his health. Tor example, an applicant with an arrested tubercu losis who seeks work in certain dusty occupations, if allowed to engage in such work might readily convert an inactive tuberculosis into an active one; thereby, endangering life or at least seriously impairing the applicant's future effic iency and earning capacity, fhereae the same applicant, if assigned to a posi tion that involved no such exposure, might be expected to continue for years as a useful and productive workman. The examination of applicants for employ ment likewise protects those that are already employed from the risks of communicable diseases such as tuberculosis and various acute respiratory and other infections being introduced into their midst by a new applicant. Many of the younger individuals who seek employment have never be fore received & thorough physical examination and consequently are unaware of the defectB from which they suffer, As a result of physical examinations, many defects are located which may be removed or corrected before they have caused irreparable damage, thereby Increasing the efficienqr of the worker and often averting definite and finally chronic diseases. Furthermore, incipient tuber culosis, unsuspected diseases of the heart, kidneys, and a host of other dis eases of a similar nature are discovered and the applicant referred for proper medical care and treatment which otherwise might have been postponed until too late. As briefly stated by that great Italian investigator and father of in- \ dustrlal medicine, Bernardino Bamaizini, "A danger forseen is half avoided, a disease known is half cured." -5- Of eves more importance than the initial physical examination of applicants is the periodic examination and care of old employees hy an indus try. Such a procedure serves to check the efficiency of preventive measures designed to prevent occupational diseases. It offers the most effective way of controlling the health of large grotq?s of workers by discovering early sot only occupational diseases, but many other conditions that go undiscovered until the worker is acutely ill or becomes diseblud. If the various conta gious conditions go unrecognised others become infected, thereby causing ser ious economic loss as well as endangering the health of a group of Individuals. The information obtained from physical examinations affords the medical supervisor the opportunity to make certain that enployeee are engaged in suitable work out of which they are getting results, to correct the effects of undue exposure to harmful environmental conditions, and generally . to lessen all occupational hasarda. As a public health measure', it Is impos sible to over-estimate the value of such periodic examinations in establishing among employees Interest in sickness prevention. for a long time the importance of accident prevention hae been well recognized by industry. She very earliest attempts at industrial medicine consisted largely in the prevention and treatment of accidents occurring in the course of employment. By systematic work along educational lines and establishment of safety department* supervised by trained personnel the occur rence of serious accidents, many of which were considered aB unavoidable, has been enormously reduced. The problems today that confront all industries are how to bring about a like reduction in diseases, particularly those associated with or initiated by the so-called hazardous occupations. -6- Siace actions for damages on account of diseases due to alleged negligence of the employer are being brought with increasing frequency in the civil courts a great many bills have been introduced in state legislatures for the purpose of bringing certain occupational diseases under the compensation acts. At the present time considerable discussion as to the advisability of including the most important of the lung diseases caused by dusts, namely silicosis, under the condensation law is heard. Despite the fact that silicosis Is always purely an occupational disease, none of the state workmen's condensa tion laws in the United States specify silicosis as a compensable occupational disease, with the exception of Kentucky which pasted an amendment, effective June l4, 1934, permitting employers in certain industries subject to the silica dust hazard to voluntarily place themselves under the workmen's condensation act with respect to the disease illcoele. Of the eleven states and three territories in which occupational disease is compensable, five have schedules of diseases which ehall be covered, and none of these lists silicosis, so that it is definitely not compensable in those states, namely, Illinois, Minnesota, Sew Jersey, Sew fork, and Ohio. In six states and two territories and in the District of Columbia, there is more or less general coverage for occupational diseases, and silicosis may be held compensable under the laws of California, Connecticut, District of Columbia, Kentucky, Massachusetts, by mutual consent of enployer and employees in Missouri, and in North Dakota and Wisconsin. She governors of a few states have appointed commissions to study the methods for bringing diseases caused by certain dusts under the condensa tion act and for promoting preveutlve measures. Very valuable and interest ing reports have been leaned by such eeaalasions in the states of Pennsylvania and Massachusetts, while Hew Jersey, Illinois and Wisconsin have studied the situation Intensively. The Massachusetts and Wisconsin consul siions recommended regulations for the preventive measures, since the disease is already a condensable one in these states. The Massachusetts ccannisslon's recomnendatlons included compul sory physical examinations on entrance to certain specified hazardous employ ments and periodic examinations throughout exposure, neither of which was carried througi. The Industrial Commission of Wisconsin has developed and put into effect a code which attempts to define what constitutes a harmful concen tration of various injurious dusts and establishes a "safe limit" below which the atmosphere of workrooms must be maintained. The Pennsylvania Commission recommended a scheduled list of diseases and special provisions for the coopensation of disabled workers with strong emphasis on a medical board of control such as exists in the administration of occupational disease compensation and silicosis acts in operation throughout the British Bnplre. These references serve to indicate the trend of present-day thought with respect to control and diagnostic measures. Control measures cover a wide scope of conditions to be standardized, which, beside physical examinations, include methods of determining the extent of hazards; equipment designed to protect the workers;, and the elimination or control of contributing factors. These problems can be solved only by the combined experience of trained men in the various sciences. The diagnosis of the diseases resulting from exposure to Industrial hazards and the extent of disability incurred obviously should be entrusted to medical men specially qualified for this work with facilities for -8- adequate radiological examinations. Disputed cases should be referred to a board composed of trained personnel capable of coordinating the medical, radio logical t and pathological examinations as well as the results of scientific investigations. She action of such a board of specialists should be final. She set up of a proper program for medical control of workers exposed to dust depends upon the number of employees involved and individual plant con ditions. X series of articles under the title of "She Medical Department Manual" by Dr. Eart E. 71sher, being published at present in the corrent numbers of "Industrial Medicine", gives a very oocprebenslve account of the organization, operation, and routines of a medical department. These articles no doubt will be available later in book form and should be read by everybody concerned in the control of industrial health hazards, any number of Instances of adequate medical supervision of workers might be listed, differing from one another in certain respects, but all retaining the essential features of control measures. Briefly, these include: 1. She establishment of a medical department with adequate facili ties and medical personnel which has qualified in the field of industrial medi cine. A process analysis of all operations In the plant should be made and the medical supervisor should list all poeeible health hazards and familiarize him self with their physiological effects. If necessary, he should conduct research studies to determine the harmful effects of new substances introduced into plant processes about which little is known. In cooperation with other departments, he should Investigate the extent of the hazards and devise measures of control. 2. The routine examination of all applicants for employment. The procedure should include a detailed history of the applicant's previous illness -9- es and accidents classified under (a) diseases of childhood, (b) general in fectious diseases, (c) respiratory diseases, (d) venereal diseases, and (e) accidents and resulting physical defects. A. detailed history of previous occu pations engaged in is very important. The mere statement of the type of indus try in which the applicant was engaged has slight value, if ary. The exact duties performed in each occupation should be noted and information ascertained as to the probable length of exposure to haxardous substances. After the his tory has been taken and a photograph for identification purposes made (if part of routine), the applicant should be directed to the examining room vhere he is instructed to remove his clothing for physical examination. This examin ation should be made as complete as is considered necessary to determine the applicant's physical condition. If the applicant has baen or will be exposed to dusts which induce lung diseases, an X-ray picture of the chest Is an important part of the exam ination. This part of the examination may be referred to an experienced roentgenologist, as the value of this method of diagnosis depends upon the type of pictures taken and the experience of the reader who interprets them. The examining physician also may need additional information obtained by laboratory analyses of the blood, sputum, and urine. These aide to diagnosis should be provided or made available when desirable. 3. The rating and placement of applicants. In cooperation with the personnel department, the applicant should be rated and placed, not only on his training and past experiences, but also on his physical and mental abilities ,,o fill vacancies occurring from time to time. The record of Ms physical and mental examination should be the confidential property of the medic*! depart ment. -10- U. Periodical physical elaminations. She frequency of periodical examinations necessarily must depend upon individual circumstances according to the need for such examinations as determined hy the supervising physician. There physical examinations are made for the first time, the employees of long standing should he given snple explanation of the benefits of such examinations and he given aBSurances that their jobs ore secure. 5 Provision for the dieahled. Employeee eho develop disabilities during the course of employment ahould he re-assigned to occupations which will not interfere with or aggravate the disability, or they should be provided for in other waye. No program of supervision can be effective or even endure which does not include these essential features conducted with fairness and in good faith toward all concerned. Shployese want, above all elee, security of employment and any attest to use the periodical physical examinations as a means for eliminating those who contract disabilities incident to occupation without pro viding for their needs, will meet with determined opposition. Physical disa bilities need not disqualify a man for work, but, rather, Indicate the types of work he can do and not endanger himself or others, thereby prolonging his years of usefulness and adding to his enjoyment of life. Many concrete exauqiles might be cited of results obtained through dust control measures and coapetent supervision of workers. One which strikingly illustrates the value of such measures la the experience of the South African gold mines. During the years 1918-20 the production rate for silicosis for those who had 10 years underground service amounted to about 10 per cent. The highest rate for those having 16 years service amounted to lU.5 per cent. Dur ing the years 1920-23 the production rate for those who had 10 years of service -11- dropped to 5 per cent -and during the year 1931-32 the rate dropped to a fraction over 1 per cent. The highest rate during the 1920-23 period amounted to a little over 7 per cent with 16 years' service and in the period 1931-32 the highest rate was about per cent after 18 years of service. This experience can he dedicated wherever preventive measures are effectively applied.