Document 93apdE1Y6Nxm7V0BxGypZxdb7

os Infection of the ireila pestis. J. Hyg. bowaz, E. J. Cassell, 's Health and the UrAir Pollution, Weath^oid. Amer. J. Pub. Los Angeles County, anford Research Inlia. Cited in Amdur. ifuric Acid Mist to ih. Ind. Hyg. Occup. . Vanderpol, D. S. and N, C. Ahlquist: m Sulfate Aerosol: e St. Louis Region. Asbestos Emissions from Baghouse Controlled Sources COLIN F. HARWOOD. Ph D.. DAVID K. OESTREICH*, PAUL SIEBERT and JOHN D. STOCKHAM HT Research Institute. 10 IVest 35th Street. Chicago, Illinois 60616 There is virtually no information published on the absolute efficiency of bagbouses in reducing the emissions of fine particles of asbestos. This lack of information is un fortunate because serious occupational health problems may result from the common practice of recirculating air to conserve energy. Emission testing has been conducted at five asbestos processing plants where the emissions are controlled by bagbouses. The results showed that the mass removal efficiency frequently exceeded 99.00%. Membrane filter samples of the effluent were examined by optical and electron micro scope. It was observed that despite the high mass efficiency, the number of fibers emitted, which were greater than 1.5 Am in length, was about 10+-105 fibers/m3, while the number of fibers less than 1.5 m was 10;-10* fibers/mL The significance of the size of tbe fibers in terms of probable health impact is briefly discussed. its 89th Bridges, d instru cts, food ation of ials and ollutants :hromatrms will For inlalytical 20044. equency >bjective jerstand usan P. rochure, ya. The 615 N. Introduction number of fibers from a given volume of air A RECENT SURVEY of asbestos processing plants revealed that baghouses by means of optical and electron microscopy. The use of an electron microscope enabled are by far the most common device for con the smallest fibers, as small as 0.02 fim in trolling the emissions from these sources.1 Asbestos has been declared a hazardous pol lutant by the EPA, is known to cause as- diameter and 0.06 fim long, to be counted. The procedure used by the authors is quite different from the OSHA procedure3 which bestosis and is strongly associated with the requires that only those fibers longer than formation of cancers, particularly mesotheli oma. It is surprising, therefore, that a review of the published literature has revealed only 5 /xm be measured. At > 5 /xm, unambigu ous measurements by multiple observers may be made using the relatively simple optical one reference to the efficiency of baghouse microscope with phase contrast at 430X. devices to limit the emission of asbestos fi The occupational health standard is based bers. In that paper,2 the efficiency was on information gained on the incidence of quoted simply as 99.992% on a mass basis asbestosis among those workers occupation- and no details were given of the measure ally exposed to asbestos at know concentra ment technique used. tion levels of fibers greater than 5 fxm. This paper details the efficiency testing of The importance of this study in terms of j baghouses located at five asbestos process ing plants. Information was obtained, not industrial hygiene is that it gives information on the possible consequences of the common only on the mass efficiency of the dust col practice of recirculating air from the bag- lector, but also on the efficiency as a function house back into the plant. The relationship of the size of the fiber challenging the filter. between asbestos particle size and the induc Size efficiency was obtained by counting the tion of cancer has not yet been established; until such time, it is prudent to quantify the EPA Technical Center, Relearch Triangle Park, North Carolina Z77I1. concentration of fibers of all sizes present in plant air. August, 1975 American Industrial Hygiene Association Journal J95 Feature Location Product Baghouse Make and Model Baghouse Capacity m3 min ~1 (cfm) Air to Cloth Ratio cfm:ft2 Number of Compartments Total Number of Bags Bag Size Diameter, cm Length, m Bag Permeability cfm:ft2 at 0.5" h2o Bag Construction Material Weave Thread Count Pressure Drop In HjO Cleaning Cycle TABLE I Baghouse Specifications 1 Waukegan, Illinois Asoestos Cement Parsons Special Design 2 Denison. Texas Asbestos Cement Wheelabraior Model 26 Plant 3 Marshville, N.C. Asbestos Textiles Wheeiabrator Model 112 4 Asbestos, Quebec Milled Asbestos Wheeiabrator Special Design 5 Eden Mills. Vermont Milled Asbestos Wheeiabrator Model B-607 Series VIII 1.132 (40,000) 2.0:1 4 800 736 (26,000) 2.6:1 1 784 473 (16.000) 3.0:1 1 304 127,000 (4.500,000) 3.0:0 8.490 (300,000) 3.2:1 11 8 79,200 2,688 12.7 (5") 3.05 (10") 12.7 (5") 20.3 (8") 3.18 (10'5") 2.82 (9'3") 12.7(5") 4.27 (14') 20.3 (8") 5.33 (17'6") 15 5 15 5 15 ;!r 5 25 16-20 Colton Sateen 6 Mechanical Shake Cotton Sateen 96x60 5.7 Mechanical Shake Cotton Sateen 2.2 Mechanical Shake Cotton Sateen 3 Mechanical Shake Cotton Sateen 96x60 4 Mechanical Shake Experimental ~Piant Location Five different plant locations were se lected for study. The basis for the selection was the nature of the asbestos processing category which they represented. They in cluded: two asbestos ore refining mills, two asbestos cement product plants (where the asbestos fibers can be considered to be bound into the product), and an asbestos textile plant'(where the asbestos fibers can be considered as loosely bound). In ail the locations, chrysotile asbestos was used ex clusively. Baghouse emission control devices were used at all the locations, and details of the baghouse construction and operation are summarized in Table I. These installations are typical of good, accepted modem practice in the industry. Recirculation was practiced at three of the five locations in order to con- 596 Anf'usr, 1975 I 01iS`J0(jlS J Eden Mills, Vermont Milled Asbestos ator Wheelabrator Model B-607 Series VUI 0 8.490 0) (300,000) 3.2:1 8 2.688 20.3 (8") 5.33 (17'6") 16-20 Cotton Sateen 96x60 4 1 Mechanical Shake sbestos fibers can >ound). In all the tos was used ex- trol devices were ind details of the id operation are ~hese installations d modem practice ion was practiced is in order to con- ,4 l'i?5 Filter Holder serve heat during the winter months. Sampling Procedure Sampling was conducted using, where pos sible, the EPA procedure detailed in the De cember 23, 1971, Federal Register. 36, 247. Two standard, EPA Method 5, isokinetic sampling systems as shown in Figure 1 were utilized to allow simultaneous sampling both upstream and downstream of the baghouse. The sampling probes and nozzles were fabri cated from stainless steel. The probes had an I.D. of 1.27 cm (0.5 in.) and a length of 107 cm (42 in.), and the nozzles were 0.63 cm (0.25 in.) I.D. Sampling points in the duct work were se lected in regions where the most stable flow patterns existed. The ports were located, where possible, eight to ten diameters up stream from any bends, elbows, junctions, or other constrictions in the stack or duct. In SQjne instances, it was not possible to collect samples by the isokinetic sampling method. "This was because of physical limita tions in the plant design which made such points inaccessible, or because of the close proximity of accessible sections to fans or bends. Here, high volume samplers fitted with 20 cm x 25 cm (8 x 10 in.) membrane filters were used within the baghouse close American Industrial Hygiene Association Journal to the exit. On the upstream side of the baghouse, samples were drawn through a cyclone fol lowed by a 10 cm (4 in.) membrane filter of 0.8 pm pore size. On the downstream side, no cyclone was used: the air stream was led directly to the membrane filter. After sam pling, the fitter was placed in a marked plas tic folder. Material adhering to the inside of the probes and tubes was washed into a sample collector using acetone. The collec tor was then marked and sealed. Sample Arudysis The mass collection efficiency was deter mined by accurately weighing the samples collected before and after the baghouse. The filters were weighed on an electronic balance having a sensitivity of 0.1 mg. On the up stream side, the dust deposited in the probe, the sampling train, and cyclone was washed with water into a weighing bottle. It was then dried in a vacuum oven at II0C, cooled and reweighed. From these weights, the mass efficiency was calculated. Fiber Counting Optical microscope analysis was per formed using the method described in the NIOSH criteria document on asbestos.5 A 597 i portion of the membrane filter, approximate ly 1 centimeter square, was removed from the central part of the filter and mounted on a slide. Using a 1:1 solution of dimethyl phthalate and diethyl oxalate, the filter was allowed to clear. A clean cover slip was placed on top of the sample and the fiber concentration determined. The light micro scope used was equipped with phase-contrast and polarized light. The objective lens of 4 mm resulted in a total magnification of 500X. From randomly chosen fields, the number of fields for a total count of 100 fibers was noted (with a minimum of 20 fields observed), or 100 fields were ob served when the distribution was sparse. For the electron microscope analysis, a circle of the sample filter 3.5 mm in diameter was cut. This piece of filter was placed on top of a carbon-coated 100 mesh electron microscope grid. The grid with the filter on it was placed in a condensation washer using acetone as a solvent. The filter medium was dissolved away by the acetone, depositing the fibers of the sample undisturbed on the carbon substrate of the grid. The specimen was then counted on a Hitachi HU-11 trans mission electron microscope at a magnifica tion of 16.364X. The optical microscope analysis enumer ated the fibers greater than 1.5 /xm in length and a minimum diameter of 0.5 /xm. The electron microscope analysis counted fibers down to 0.06 /xm in length and 0.020 /xm in diameter. Calculation of Fiber Numbers To relate the number of fibers to the as bestos concentration in the air, the following equation was used: no. of fibers _ j no. of fibers counted m3 of air [ no. of fields effective filter area, cm2 area of microscope's field of view, cm2 ; 1- volume of air sampled, m3 J where: Effective filter area = 81.7 cm2 for 4 in. filter in EPA train Effective filter area = 63.2 cm2 for 4 in. Hi-Vol filter Effective filter area = 425.4 cm2 for 8" x 10" Hi-Vol filter Area of field of view = 6.514 x 10-'* cm2 for optical microscope (500X) Area of field of view = 1.344 x 10~7 cm2 for electron microscope (16,364X) -H ^ Efficiency Calculation To calculate the effiicencies, both by mass and by number, the following relationships were used: Mass Efficiency (% ) = 100 Number Efficiency (% ) = 100 Mass in a given volume of air after the baghousc Mass in the same volume of air before the baghouse No. of fibers per cubic meter after the baghouse No. of fibers per cubic meter before the baghouse Results Mass Removal Efficiency The mass efficiencies of the five baghouses are given in Table II. It is observed that the efficiency is extremely high and, in all in stances, exceeded 99.99%. At two locations, the mass collected on the upstream side of the filter was too small to be weighed, al though a faint coloration of the otherwise pure white filter could be observed. Fiber Removal Efficiency In Table III, the number of fibers up- 598 August, 1975 'sis counted fibers 1 and 0.020 /xm in ers f fibers to the as: air, the following >ers counted of fields X a, cm2 1 of view, cm2 1.7 cm2 for 4 in. 3.2 cm2 for 4 in. :5.4 cm2 for 8" x 5.514 x 10-4 cm2 500X) 1.344 x 10-7 cm2 (16,364X) :ies, both by mass wing relationships he baghousc : the baghouse j ?aghouse I baghouse j upstream side of j be weighed, alof the otherwise bserved. ber of fibers up- August, 1975 TABLE II Mass Removal Efficiencies for Baghouse Controlled Asbestos Emission Sources at Five Plant Locations Plant Location Sampling Location Volume of Air Samples (mJ) Total Mass of Dust Collected (g) Concentration of Dust Collected (g. m-3) Mass Removal Efficiency (%) Waukegan, Illinois Upstream Downstream 1.755 12.984 7.6092 0.0000 4.336 0.000 100.0 (within experimental limits) Marshville. N.C. Upstream Downstream 2.765 6.404 1.5894 0.0002 0.5748 3.120x 10-5 > 99.99 Denison, Texas Upstream Downstream 4.183 195.0'1' 53.9653 0.0000 12.901 0.000 100.0 (within experimental limits) Asbestos. Quebec Upstream Downstream 0.0014 I01.8(1) 0.1648 0.0103 117.7 1.011 x I0"4 > 99.99 Eden Mills, Vermont Upstream Downstream 3.085 143.0'11 17.9220 0.0084 5.809 5.874 x 10-5 > 99.99 Note: All samples taken isokmeucally by EPA Method 5 except those marked (1), which were taken by hi-vol sampler. TABLE m Upstream and Downstream Fiber Concentrations and Removal Efficiencies for Baghouse Controlled Asbestos Emission Sources at five Plant Locations Plant Location Waukegan, Illinois Marshville, -N.C. Denison, Texas Asbestos. Quebec Eden Mills, Vermont Sampling Location Upstream Downstream Upstream Downstream Upstream Downstream Upstream Downstream Upstream Downstream Fibers Counted by Optical Microscope at a Magnification of 5O0X Fibers per Cubic Meter Removal Efficiency % > 1010 6.4 x 103 > 99.99 8.1 x 10 1.4 x 104 > 99.99 1.0 x 10 2.9 x 104 97.18 2.2 x 109 8.2 x 10s 99.96 1.4 x 10* 4.5 x 104 > 99.99 Fibers Counted by Electron Microscope at a Magnification of 16.364X Fibers per Cubic Meter > low 1.1 x n>7 Removal Efficiency % > 99.99 2.5 x 10l 3.3 x 109 98.69 3.2 x 107 1.4 x 107 57.90 1.2 x 10'* 1.4 x 109 99.88 1.4 x 1013 1.3 x 10* > 99.99 American Industrial Hygiene Association Journal 1 TABLE IV The Number of Fibers Exiting from Five Baghouse Controlled Asbestos Emission Sources as Counted by Optical and Electron Microscopes Plant Number of Fibers Exiting Greater than 1.5 Mtn weight Number of Fibers Exiting Greater than 0.06 Min length Location Concentration Fibers m-3 Number per Minute Concentration Fibers m-3 Number per Minute Waukegan, Illinois 6.4 x 103 7.2 x 10 1.1 x 107 1.2 x 101 Marshville, N.C. 1.4 x 104 1.0 x 10 3.3 x 10s 2.4 x 10>l Denison, Texas 2.9 x 104 1.4 x 10 1.4 x 107 6.6 x 10 Asbestos, Quebec 8.3 x 105 1.1 x 1011 1.4 x 10 1.8 x 10'4 Eden Mills, Vermont 4.5 x 104 3.8 x 107 1.3 x 10* 1.1 x 10" in _4 CD CD CD Cl cn o -c~ stream and downstream of the five baghouses are presented. In general terms, the number of fibers greater than 1.5 fim in length exiting from the baghouse is of the order of 104 fibers per cubic meter, while the number of fibers greater than 0.06 fim in length is of the order of 108 fibers per cubic meter. A similar ratio is found in the number of fibers approaching the baghouse, where 109 and 1013 fibers per cubic meter of greater than 1.5 /im and greater than 0.06 fim are found, respectively. Very high removal efficiencies are found in all instances. Based on the available data, it does not appear that the removal efficien cies are size dependent. Similar efficiencies are found with the greater than 1.5 fim fibers and the greater than 0.06 /xm fibers. One ex ception to the very high efficiency values oc curred at Denison. At this location, high grain loadings were observed in the upstream duct, and it is possible that partial blockage of the probe prevented fibers from reaching the filter. The number of fibers on the down stream side was comparable to the other lo cations. Despite very high collection efficiencies, very large numbers of fibers were found to 600 exit from the baghouse. This is shown in Table IV, where the total number of fibers exiting per minute and their concentration in the air stream has been tabulated for each plant location. Discussion The Recirculation of Cleaned Air The result of a survey taken as part of this study has revealed that the recirculation of air exhausted from baghouses used to clean asbestos dust from air is common practice in the industry. The American Conference of Governmental Industrial Hygienists has the responsibility through the Ventilation Committee of publishing a Manual of Rec ommended Practice, which establishes the governmental recommendations as regards the recirculation of air within a plant. These recommendations are considered and cited in the standard of the Occupational Safety and Health Administration (OSHA) of the U.S. Department of Labor. The recent energy crisis has occasioned a need to conserve heat as a national policy. Prior to this, regulations prohibited the re circulation of plant air containing hazardous materials even though recirculation was cco- AttKHSt. 1975 lissioo Sources >ers Exiling than ength Number per Minute 1.2 x I010 2.4 x 10" 6.6 x 10* 1.8 x 10" 1.1 x 10" This is shown in al number of fibers teir concentration in tabulated for each meet Air taken as part of this the recirculation of fuses used to clean 5 common practice aerican Conference rial Hygienists has th the Ventilation a Manual of Recich establishes the iations as regards thin a plant. These isidered and cited ccupational Safety n (OSHA) of the r. > has occasioned a a national policy, prohibited the re naming hazardous rculation was eco Aukwu, 1975 nomically attractive. This regulation was predicated upon the premise that no control device is foolproof. A temporary loss in con trol efficiency would create considerable risk of exposure of workers to dangerous levels of toxic materials. The impact of the energy crisis has led the ventilation committee to propose circum stances which would allow the recirculation of cleaned air, provided certain criteria were met by the system. A formula has been pro posed which would establish the limits of contaminant concentration in the exiting air; CR = Vi (TLV - Co) x-g- x -i- where Cr = maximum permitted concentra tion of contaminant in exit air from the collection after cleaning, in any consistent units TLV = threshold limit value of contami nant Co = concentration of contaminant in workers breathing zone with local exhaust discharged outside Qt = total ventilation flow through af fected space, cfm Qr = recirculated air flow, cfm K = an "effectiveness of mixing" fac tor, usually varying from 3 to 10 It should be remembered that this equation has only been proposed, not accepted, at this stage. For asbestos, the TLV value would be that presently accepted as the OSHA standard, that is, 2 fibers per cubic centimeter (where a fiber is greater than 5 gm and with an aspect ratio of greater than 3:1 length to breadth). As has been shown, only a small portion of the true asbestos con centration in the recirculated air is accounted for by this standard. Two methods are proposed that would in crease the safety of such a system and guard against a temporary breakdown in the collec tion efficiency. One is that a back-up filter should be fitted to remove the contaminant in the event of a failure of the primary con- American Industrial Hygiene Association Journal trol. The application of such a system would obviously add considerably to the costs. The second method would be to use a monitor which would stop the recirculation, or acti vate a rapid acting by-pass to the outside air, in the event of a failure of the collector. The problem would be to produce a monitor for asbestos which would be fast acting and modest in cost. At the present time, no such monitoring device exists for asbestos, despite considerable research effort to achieve this objective.4 Exposure Levels for Asbestos The present accepted standard for asbestos exposure has been determined by OSHA to be 2 fibers per cubic centimeter, for fibers longer than 5 /am. The measurement method and the rationale behind this exposure level is well presented in the NIOSH document "Oc cupational Exposure to Asbestos".5 The selection of the size of 5 /urn as the shortest size of the fibers which are counted stems from British practice.6 The British use this criteria for two reasons. Firstly, it represents that size which is readily detect able using a relatively simple optical micro scope, while detection for smaller fibers and particularly submicron fibers requires the use of an electron microscope, which is both time-consuming and costly to use. Secondly, a wide body of information on the exposure levels and incidence of asbestosis has been generated over many years using the 5 gm size limit in establishing the exposure levels. Thus, the use of the optical microscope gives an index of exposure which has had wide practical applicability. The problem with using this index is that the ratio of the numbers of fibers greater than 5 gm in length to those less than 5 pm in length is very much a function of the in dustry. Thus, textile-producing industries have a greater proportion of longer fibers than, for example, those industries using as bestos as a filler in plastics or paints. The fiber size considered to be most dan gerous is not established at this time. Evi- 601 SOSli'JUUlS ST0065506 dence in the literature on this subject is con fusing and reveals the uncertainty. Stanton7 has performed experiments that have indi cated that fibers, including fibers of mate rials other than asbestos but having a simi lar morphology (e.g., alumina), in the size range of 10-100 ftm are most harmful, and that their ability to produce tumors decreases with decreasing length. However, his findings have been criticized because of the method of application. The method required that 40 g of the powdered asbestos be placed in con tact with the pleura and held in place by a fiber glass patch attached surgically. Thus, the normal free movement of the particles was prevented. This work might also be criti cized from the standpoint that, in all proba bility, the larger fibers do not find their way through the human body defense mechan isms. Pott,8 on the other hand, has performed experiments using asbestos dry milled to a fine size. Two size groups were used, one with 95% of the fibers less than 5 /xm, and a second with 99% of the fibers less than 3 gm (with 93% less than 1 pm). The size was checked by electron microscopy, which also showed that the fibrous structure had been retained through the grinding process. It was found that with both groups, tumors developed in 40% of the rats after intraperitonea! injection of the asbestos. How ever, the small sized fibers required a longer incubation period than the larger fibers (about 20 months versus 12 months) to achieve the 40% tumor level. A further important point when discussing the exposure index for asbestos is that it is based on the probability of a worker con tracting asbestosis, not cancer. With the present exposure levels, the probability of a worker getting asbestosis is 1 % if a 30 year working life in the industry is pursued. There is no definitive information on the chances of developing a cancer. Recognition of the carcinogenic aspect of asbestos is compara tively recent, and it is estimated that, in hu mans, a 30 year incubation period is required before the cancer develops. Therefore, there are no adequate dose records upon which to relate the delayed response. Reasonable scientific predictions are made based on animal experiments but, because of the massive doses used to accelerate the in cubation period, there is justifiable doubt as to the conclusions reached. Again, a de gree of susceptibility r.-.ay be required within an individual such that a small dose might be fatal to him, while a much larger dose would leave a second person unaffected. It is apparent from the literature that there are many unanswered questions about the danger associated with asbestos. Until the answers to these questions are more clearly understood, asbestos should be treated with caution. Conclusions Baghouses used for the control of asbes tos emissions have been shown to operate at very high efficiencies on both a mass basis and on a number of fibers basis. Even with these high efficiencies, there are substantial numbers of fibers which penetrate the fabric filter. Recirculated air may contain enough fibers to be of concern from the standpoint of cancer induction but the dose/response relationship between asbestos exposure and cancer is not well understood. There is cer tainly, a possibility that a human health penalty could off-set the economic advan tages of recirculation. If bag failure results while recirculation is being practiced, the probability of undesir able health_effects could be expected to in crease substantially. It is recommended that a rapid-acting detection system be developed which would activate a by-pass system in the event of a bag failure. It has been shown that recirculated air contains weli below the current Threshold Limiting Value of 2 fibers per cubic centi meter (fibers equal to or greater than 5 ft.m in length). This would imply that workers would be protected from asbestosis unless the bags were to fail. 602 August, 1975 . Therefore, there >rds upon which to e. edictions are made nts but, because of ) accelerate the in, justifiable doubt :hed. Again, a debe required within mall dose might be t larger dose would ffected. literature that there uestions about the isbestos. Until the is are more clearly lid be treated with [ j j ' ! i * j | References t. Harwood. C. F.. P. Siebert and T. Blaszak: Assessment of Particle Control Technology for Enclosed Asbestos Emissions. Report No. EPA 650/2-74-088, October. 1974. 2. Goldfield, J. and F. E. Brandt: Dust Control Techniques in the Asbestos Industry. Presented at the Amer. Ind. Hyg. Conf.. May. 1974. 3. Edwards, G. H. and J. R. Lynch: The Method Used by the Public Health Service for Enumer ation of Asbestos Dust on Membrane Filters. Ann. Occttp. Hyg. II.1 (1968). 4. Rossi, R. C., C. A. Gaulin. R. M. Gerber and H. L. Van Passen: Evaluation and Develop ment of Instrumentation for Process Control of Air-borne Asbestos. Interim Report, EPA Grant No. R8O2394-0I. April. 1974. (Private communication. Bruce Harris. Project Officer). 5. Occupational Exposure to Asbestos. U. S. Dept, of Health. Education and Welfare. HSM7210267 (1972). 6. Standard for Asbestos Dust Concentration for Use with the Asbestos Regulations. 1969. Dept. of Employment and Productivity, Her Majes ty's Factory Inspectorate, Technical Note 13 (1970). 7. Stanton, M. F. and C. Wrench: Mechanisms of Mesothelioma Induction with Asbestos and Fibrous Glass. J. of the Nat. Cancer Inst. 4S: 797 (1972). 8. Pott, F., F. Huth and S. Friedrichs: Tumors of Rats After IP Injection of Powdered Chrysotile and Benzo(a)pyrene. Zbl. Bakt. Hyg., I. Abt. Orig. Bl55.463 (1972). The help and cooperation of /ohns-Manville, Raytx'jlos, and GAP in performing these studies is gratefully acknowl edged. The help of Erdmann Lubecke, Tcm Blas/aJc. Dr. Ranade. Anant Somudra. and David Becker of the 11TRI staff is also acknowledged. fOSSDOOiS e control of asbesshown to operate n both a mass basis s basis. Even with ere are substantial penetrate the fabric ay contain enough rom the standpoint the dose/response estos exposure and tood. There is cera human health economic advan- ile recirculation is ability of undesirx expected to inrecommended that ystem be developed -pass system in the iat recirculated air current Threshold rs per cubic centigreater than 5 fim imply that workers a asbestosis unless August, 1975 George D. Clayton & Associates Renamed Clayton Environmental Consultants, Inc. Now a Marsh & McLennan company, Clayton will deliver technical and professional services to clients on a uniform international basis. Founder George D. Clayton will serve as chairman, based in Fallbrook, California. Alonzo C. Rand is president and Truman F. Maxwell has been appointed operations manager at Southfield. Founded in 1954, Clayton's environmental control programs service in dustry and government in the areas of air, water, noise, radiation, food and drug, industrial hygiene, agricultural chemistry and solid waste pollu tion. Robert D. Soule heads industrial hygiene activities. Stern Becomes President of Air Pollution Control Association Dr. Arthur C. Stern now is president of the APCA. An international authority on air pollution control technology. Dr. Stem is Professor, De partment of Environmental Sciences and Engineering, University of North Carolina, Chapel Hill, NC. October Meeting to Feature Fabric Filtration Equipment The Niagra Frontier Section of the Air Pollution Control Association " will conduct a 2nd international specialty meeting on "The User and Fabric Filtration Equipment" at the Statler Hilton in Buffalo, NY. Dates are October 6-7, 1975. The conference is said to be aimed at the user, with emphasis on the baghouse process. Theory, methods, systems and case histories will be explored. Leading manufacturers will exhibit fabric filtration equipment. For information, contact I. Arthur Hoekstra, Air Pollution Control Division, Erie County Dept, of Environmental Quality, 95 Franklin St., Buffalo. NY 14202 (716) 846-7762. American Industrial Hygiene Association Journal 603