Document 7O3X2ZdgxXp5Rvxqw0EDpLyz6

292 September, 1956 complaint* if there were no threshold limits. In conclusion a few remarks are in order dealing .with the philosophy of and justifica tion for threshold limits, and are added here because they serve as a reply to the criti cisms often leveled at industrial hygiene standards. It Is not unusual to hear that these limits are useless, if not even dangerous, because in the event that the atmospheric concen tration is measured inaccurately, reliance on the standards creates a false sense of se curity on the one hand, or needless alarm on the other, depending upon whether the measured result is in error downward or upward. It requires little mental gymnastics to realize that this is equivalent to con cluding that there is no sense in asking your grocer for a dozen oranges simply because he may make a mistake in counting them. By definition, threshold limits are those concen trations of contaminants which in the light of current knowledge will not cause harm to persons exposed continuously day in and day out during the normal working hours. Reference is to the concentration actually existing, not to some value that the investi gator might conclude exists. Concentrations can be measured accurately, but to do so re quires skill, understanding, patience and energy. It Is rather discouraging to note how frequently conclusions arc based on wholly inadequate data/It is not surprising either that the concentrations frequently "measured" have Uttle relation to the true weighted average concentration. The philosophy of threshold limits is that each one represents n concentration of the substance in question that will have no demonstrable adverse effect on the health of exposed persons. Not all persons react the samet'to stimuli of this nature, but rather any given population follows Approximate ly an average random distribution pattern as regards response to atmospheric contami nants. That is to say, there is an occasional person at one end of the curve who is un affected by relatively overwhelming concen trations and there is an occasional person at the other end who is affected by extreme ly low concentrations. To prevent any ad verse effect upon every last man may require such low concentrations as to be impractic able. The threshold limit is merely a con centration that intersects the random dis- tri button curve at a very low point. How low this point is for any substance cannot be stated. That it is not the same for all ma terials is obvious, and that it serves to pre vent harm to all but a relatively few is obvious, also. Serious or irreparable damage to the occasional person who falls to the left of the threshold limit on the random dis tribution curve can be avoided bv an appro priate medical examination program. References I. American Standard* Safety Cede for Ventilation and Operation of Open SurCace Tanka. Z-t.l, New York. 1451. - S. Dramdt. A. O.: Exh*u*t Spatem*. Elect,rap latin* En*iaerin Handbook. Chapter IT, KelnhoM PubHihinr Corporation. New York, I95S. X. McConnell, W. J.. funk. R. H.. and Bnam or. A. Ik: Occupational Diuua in Government-Ow nwt Ord nance Expleaivee Plant*. Oeeup. Sid, 1 :U141I, June, IMS. 4. McC">`neU, W. J.. and FtlS.v, H. H.: Summary of Twenty-Two Trinitrotoluene Fatalities in World War II. J. hidv*<. Mug. JJ Torie., 26:?G-6. May. MM*. Prepared Discussion ARTHUR C. STERN, Chief Air Pollution Community Program Robert A. Taft Sanitary Engineering Center U.S. Public Health Service Cincinnati, Ohio IN AN ENDEAVOR to safeguard the health of the worker and the public from exposure to harmful substances, two basically differ ent types of standards have evolved. One type--the threshold limit, or maximum al lowable concentration--is the performancelypc of standard. The other, about which Uttle has been said by the previous speakers, is the engineering type of standard. To make the distinction between the two types of standards more concrete, take the specific example of & stave-type tumbling mill (Fig. 1) in a ferrous foundry. Into it are placed castings with sand both dinging to their outer surfaces and in their internal cavities in the form of cores. The express purpose of placing these castings into the mill is to clean them of this sand. The mill is, therefore, by its very nature, a device designed and operated to cause sand to leave the castings and enter the ambient air. While it is-true that most of this sand will Industrial Hygiene Quarterly 203 fall to the floor under the mill, it is equally true that a tremendous number of free silica particles will become air-borne by the process. From the viewpoint of the perform ance standard, it is necessary to keep the atmosphere of the cleaning room below the threshold limit for free silica by whatever means the owner of the foundry may choose to employ. Engineering Standards pttOM THE VIEWPOINT of engineering stnnd** arda, the reasoning is somewhat as fol lows : A. It is widely recognized in the foundry industry that stave mills are bad dust pro ducers and require enclosure. B. The industry, by trial and error, has developed a satisfactory type of ventilated enclosure (Fig. 2) which not only keeps the dust out of the workroom, but also keeps the floor below the mill free of much of the sand that would otherwise accumulate there and have to be carted away. C. This type of enclosure, having been adopted by most of the industry, should .therefore become the standard of the entire 'industry. D. An engineering standard should there fore he written so specifying this enclosure with respect to structure and ventilation that any foundryman building an enclosure meeting these specifications will achieve dust control of his stave mill (Fig. 3). Applicability of Standards T ET us EXPLORE some of the arguments for and against each of these approaches. Both aim at the same objective--the safe guarding of the worker. The principal ar- gument in favor of the performance stand ard is that it is noboby's business except the owner's as to how he achieves control of the hazard, just so long as he does, in fact, suc ceed In so doing. The corollary argument against the use of the engineering standard is that there in no positive guarantee that once the owner has Invested his money in an enclosure conforming to the standard speci fication, the exposure of the workers in the cleaning room will be below' threshold limit. The same logic can be used to plead the case for the engineering standard. The dust load in the cleaning room air comes from many sources in addition to the stave mills (Fig. ii. If some of these sources remain uncontrolled after the slave mill has been enclosed and ventilated according to stand ard specification, it is entirely possible, even probable, that dust concentration in the room will remain above threshold despite entirely satisfactory dust control by the stave mill enclosure. Engineering standards thus have the inherent capacity to allow a step by step orderly approach toward the ultimate goal of achieving below-threshold concentrations in all parts of the plant at airtimes. , New Construction A sstrifE that a new foundry I* being de* * signed. To apply performance standards. \ September, 1956 the foundry must first be built, placed in cleaning room equipment and applying them operation, and then subjected to air sam to the best of his ability. In this situation, pling and analysis. No reputable and well- argument arises, not as to the need for such informed* engineer would design -this new engineering standards, but rather as. to plant, without seekiitg ' the engineering their accuracy. Should the opening for air standards for the control of dust from the be 3,/:>~ or should it be 4M? If the standard says 900 cfm. and the de signer is firmly convinced that 450 cfm are sufficient, he should be prepared to back up his independence of judgment by later proof that concentrations are be low threshold in the com pleted workroom when the lower value of cfm is em ployed. But what if the designer reluctantly makes the ca SECTION THRU HOLLOW TRUNNION TUMBLER Cue* vetoety tlCOOffiM. Entry *ns `ZON 40VP(doptnitondesign) STAVE MILL (END SECTION} Duct vrttodty * 35QDFFMnrnnurrt Entry ton cnot r"tt> tote -oftOZS 050VP pacity 900 cfm to conform to the standard? Is there equal necessity for the sponsors of the standard to guarantee compliance with Square ml tkferPom et lb to 24 met 25 to 50 " 5tto56 * 37*42 ` 45 to 48 ' EXHAUST VOLUMES Rajrwt milt t.D nncOei Up to 24 cUW 24 - 50 Jo - X 56 - 42 42-46 4$ - 54 CFM Ttunnon Store* 4JO 680 980 1530 1750 2200 600 900 930 1550 1750 2200 the threshold limit? The difftculty of so doing in the possible presence of ex traneous sources of the con taminant that have already been mentioned almost in variably makes it impossi ble for the sponsor to un dertake such guarantees. 49 to 54 " 55 to CO ' 54 - 60 60 - 66 2730 3500 2730 3500 Double Jeopardy 6/to 66 " 66 - 72 5020 3920 YWJiERE the engineering 6?to 72 " *For Lenft/H **> 70', increase CFM proporlrpootely 4COO 4600 standard is a tool in the hands of an enforcement Fig. 3. Tumbling mills. --M Jo IflE agency, the user of such standards' frequently fears that he is placed in double jeopardy. He has to comply with engineering standards i-----1 ---- 0<u<p.r<i9 Vn^TT] with which he may dis agree, and then, having em ployed all such standards in I :r ri every operation, may still be not in compliance with the performance standards. The wise enforcement agency will let It be known that it will not permit such double jeopardy to occur, and that any factory owner Floor plM showing logout of oquipment Including stovu mills. who adheves throughout to Industrial Hygiene Quarterly 295 the best engineering standards known to the agency will not be asked to re-do the job. What, then, is the plight of the working man caught in the middle? Is he likely to become a pawn, forced to work in an un healthful atmosphere because the sponsor ing agency is unwilling to admit a mistake as to the effectiveness of its engineering standards? We are indeed fortunate that the quality of our engineering standards is so high that such cases occur infrequently. Where they do occur, they are almost always borderline cases with respect to the thresh old limit and are well within the factor of safety built into the threshold limit itself.' Emission Standards 'T'he relationship between performance and engineering standards for in-plant atmospheres has its counterpart in that be tween atmospheric and emission standards in the field of air pollution. A major dif ference is that, whereas there arc a large number of accepted threshold limits for in plant atmosphere, there are almost no stand ards commonly accepted for the outside atmosphere. The emission standard is very much in the same position us the engineering stand ard for in-plant controls in that adherence to it by one specific stack does not guarantee the cleanliness of the air of the surrounding community. Thousands of factories have put in-plant engineering standards to the test and proven that when every source of contaminant release is controlled as specified by the applicable engineering standard, the result has been to maintain the factory atmospheric contaminant concentration be low the threshold limit. Such beautiful demonstrations, which arc easy when the atmosphere in question is confined by four walls atul a roof, become almost impossible to find in the open air over cities and towns. `-`However, it is reasonable to believe that what works in a small confined space will also eventually work in the hugest of con fined spaces, that having the inevitable in version ceiling as a roof and four topo graphical or meteorological side walls. Standard for the Open Air T Et us look once again at the principal argument for performance standard in the in-plant situation, i.e., that it is no body's business but the plant owner's as to how he achieves control of the hazard---so long as he does so. Is this doctrine equally* applicable to the air over a city? It hardly seems so. No individual owner or group of owners could or would be willing to take the' responsibility for the maintenance of a specified level of contamination of the air of the community in which they operate. They would quickly recognize the many factors over which they do not have the same measure of control that exists inside the factory building. For them, the emis sion standard is a boon. Here the argument is not with the con cept of the emission standard, but with its numerical value for a particular installa tion. One of the most interesting develop ments of the past decade along these lines has been the fact that pubtic utility power plant designers have consistently specified equipment for fly ash control to meet emis sion standards much more stringent than public regulatory bodies have required. In dustrial foresight and conscience is in this, and a number of other industrial hygiene and air pollution control fronts, well ahead of public regulatory demands. Conclusion Tn uoth these areas, this is the hope of the 1 future. The dictum of a Massachusetts court of mauy years ago that the best plants in an industry may reasonably be used to set the standard for the entire industry provides the real key to future progress. America is blessed with real industrial leadership and statesmanship. Neither in dustry's leaders and statesmen nor the pub lic will tolerate tin* acceptance of stand ards which are below the best that industry can, by example, provide. Summary 'yilERE are two general types of standards --performance type standards and engi neering standards. The former specify threshold limits. The latter specify the per formance of a particular piece of equip ment. Arguments are given pro and con as to the relative merits of these two ap proaches to the same objective--the safe guarding of the worker. The engineering standard approach is particularly valuable in new construction where no equipment 236 September, 1956 exist.* al which to measure atmospheric con lead to unfortunate problems of administra centration before designing safeguards. The tion to which brief reference may be made. similarity of engineering standards for the Under the constitutions of the various in-plant situation to emission standards for states and the powers grunted to state De atmospheric pollution control is noted. partments of Health and state Departments of Labor, there exists adequate authority Prepared Discussion for such departments to effectively control any hazardous condition injurious to health. As a practical matter, there is no THEODORC C WATERS. I LB. legal need for the adoption of codes prescrib Baltimore*. Maryland ing maximum allowable concentrations. It is fair to stale that stale Departments of Health mid state Departments of Libor T8 his comment and discussion of the ex administering divisions of industrial hy cellent paper presented by Dr. Brandt giene have enjoyed the confidence of the will be directed to the legal aspects of thepublic, including both management and r.`>; application of threshold limits in the form labor, and our several state departments of maximum allowable concentrations for have been and are doing excellent jobs in the control of air contamination. May 1 identify myself as one who has screed ns counsel for industrial organiza tions; and while my views may In* prejudiced on their behalf. 1 feel that the industrial the administration of their affairs. There fore, the use of maximum allowable concen trations should be in the until re of serv ing as a guide to industry with particular reference to engineering standards. Indus point of view is impoitartt in onr discussion of this matter. It is needless to say that today industry is prepared ami wishes to accept full responsi try lias and will continue to seek the advice of proper state departments to con trol hazardous conditions effectively, and the desired objectives will be obtained bility for the control of potential hazards through education and dissemination of in incident to employment. Simply stated, it formation through the cooperation between is good business both from the financial state divisions of industrial hygiene and standpoint and also in the promotion of industry rather than the attempted enforce industrial relationships for employers to ment of a given code as a matter of law. concern themselves with the protection of Dr. Brandt and Mr. Stern have discussed employees from all types of industrial in In detail the practical uses of threshold lim juries, be they accidental or resulting from its with the purpose of eliminating or con occupational disease. The ultimate cost of trolling occupational hazards. With all of compensation for such injuries may well ex the information presently available to ceed the cost resulting from installation of science, it is seriously to be questioned effective methods for engineering and medi whether the present schedule of recom cal control, aside Hum the fact that the em mended maximum allowances of roiicenlrn- ployer's relation to his employees is pro lion* are .scientifically correct. True, they moted when employees know that the em represent the best thinking of those scien ployer is doing everything practical to effect tists who have studied the problem; how protection. ever, it is a fact that from day to day, indus Question arises to the propriety and ad trial processes are changing, new chemical visability of the adoption of codes of in compounds are coming into commercial use, dustrial hygiene defining maximum allow and tomorrow some new problem may be able concentrations of toxic materials. The presented to industry and to public ad word "code" is defined as follows: "A ministrative agencies entirely different from body of law established by the legislative any that may have been presented before. authority of the state, and designed to regu Industry welcomes technical information late completely, so far as a statute may, the with, respect to the existence of occupational subject to which it relates/' The adoption of hazards. They will continue to welcome codes having the full force and effect of law technical advice as to practical methods of is unnecessary, inadvisable, and may well control. It must be remembered that in-