Document g5J9B2OxRoXEOyBxVD09YEmL

GPIC Drywall November /December 1975;. 21:6-8/ 30. ASBESTOS AND SILICA DUST OSHA Regulations and Exposure In Drywall Operations Harrison B. Rhodes Technology Manager and Blair L. Ingalls Supervisor, Special Projects Union Carbide Corporation Metals Division Niagara Falls. New York Introduction This two-part article is intended to acquaint drywall contractors with the current and proposed reg ulations governing the use of prod ucts containing asbestos and crystalline silica. . The concluding article in the next issue will present data on the exposure to airborne asbestos and crystalline silica (quartz) during the sanding of tape joint com pound. A total of Seven industrial locations were tested. Exposures to asbestos during the wet-out of dry-mix compounds and during cleanup II also be shown. BACKGROUND AND current status-- OSHA ASBESTOS REGULATIONS The Williams-Steiger Occupa tional Safety and Health Act was passed In 1970 with the stated ob jective of assuring, insofar as feasible, every American worker a safe and healthy workplace. Under the provisions of this act, the Sec retary of Labor issued an emer gency temporary standard for exposure to asbestos dust on De cember 7, 1971. After extensive public hearings, a permanent standard, effective )uly 7, 1972, was promulgated. The asbestos standard and the ferhods used by OSHA to develop Kvere immediately subjected to a massive legal attack by the Indus trial Union Department, AFL-CiO. In addition to the law suit. OSHA was under continued pressure from other labor groups, public interest groups, and spurred on by the news media to make revisions. It was also recognized that this was the first health standard written. As such, there were parts that were vague, parts that were impractical to enforce, and parts that were overly restrictive without a cor responding benefit in protection for the worker. During 1973, OSHA decided that the asbestos standard should be altered. The initial concept was to replace it with a series of manda tory work practices that would minimize the admittedly cumber some monitoring requirements.. The asbestos industry was asked to submit proposed work practices and a technical committee was formed under the auspices of the Asbestos Information Association/ North America. This committee consisted of representatives from about a dozen asbestos producers and large manufacturers of asbes tos-containing products. Commu nication was also maintained with trade associations that used asbes tos or its products. A draft work practice for joint taping was drawn up and submitted to the CDCI for comment The technical committee drafted several broad work practices re lating to the handling of asbestos. It soon became evident that a large number of specific work practices would be needed to cover the wide range of industrial situations where asbestos or asbestos-containing products were used. The commit tee also examined and recom mended changes in the portions of the regulations that were vague or overly restrictive. The IUD decision was an nounced in mid 1974 by the United States Court of Appeals for the Dis trict of Columbia. The court gener ally upheld the OSHA position in the matter and noted that, al though the Congress had poorly defined the procedures to be used to set such standards, OSHA had used proper methods to collect and evaluate the conflicting evi dence presented., The judgments made to arrive at the standard were within the discretion granted to OSHA; and, more particularly, the court said that it was correct and proper to consider economic fac tors. Two points were remanded for further consideration; those re lating to record retention and the time allowed for compliance. ' After the court decision, OSHA materially altered their position on the revision of the asbestos regu lations. Under heavy pressure to issue health regulations for other substances, a decision was made to amend the asbestos regulations only to the extent needed to clarify ambiguities. No changes were to be proposed in the allowable exposure levels. Many of the suggestions for clarifying language made by the AIA/NA Technical Committee were understood to have been ac cepted. The redrafting of the regulation along these lines was apparently completed In late 1974 and the re sults were submitted for review to various governmental departments as required by law and policy. Dur ing 1975 key personnel changes occurred at policy making levels In both OSHA and NIOSH. At some point, apparently quite recently, the decision was made to drop the amendment concept and reopen the entire asbestos and health con troversy. This information became public when the proposed changes sistently below the cutoff or where were published in the Federal the asbestos had been properly Register on October 9,1975. modified by a bonding agent to The asbestos standard that was prevent excessive dust. promulgated on June 7, 1972 and The revised standard proposed which i$ still in effect can be di on October 9, 1975 follows the vided intoseven main categories: same general pattern but differs in I.Sets the maximum allowable the following critical points: airborne asbestos concentra 1.The allowable exposure level tions in the workplace at a Is reduced to 5 fibers/cc long ceiling level of 10 fibers/cc er than 5 micrometers ceiling longer than 5 micrometers and and 0.5 fiber/cc longer than 5 at a time-weighted average micrometers time-weighted (TWA) for an 6-hour sh|ft of 5 average (TWA). fibers/cc longer than 5 micro 2. Monitoring and record keep; ' meters. The TWA drops to 2 ingrequirements are increased fberi/cc longer than 5 micro substantially although a pro meters in July 1976. vision to discontinue moni 2. Defines the acceptable proce toring under certain cir dures to meet these standards. cumstances Is included. 3. Defines where personal pro 3. There is no cutoff level on the tective equipment may be medical examination require used and specifies the types ment. available. OSHA has reviewed the recent 4. Specifies monitoring require medical literature on asbestos and ments and the procedures to has proposed regulations based on be used. . a very strict interpretation thereof. 5. Specifies requirements for They have not assessed the eco caution signs, caution labels, nomic (inflationary) impact of the and housekeepingprocedures. proposed regulations but have 6. Requires medical examina stated their intention to do so or tions for ail employees^ "ex- ^ ^certify that there Is no impact be- posed to asbestos." `fore public hearings are started. 7. Sets requirements for keeping The burden of proof has been of medical and monitoring placed on industry to demonstrate records. . that these regulations are overly re The standard was written in lan guage that fits conventional fixed manufacturing locations. It pre sents some very real problems, however, when applied to the con struction industry where the Job site and the work force are transi ent. The areas of particular diffi culty to drywail contractors are those dealing with monitoring and medical examinations. The AIA/ NA Technical Committee recom mended a cutoff level below which medical examinations were not re quired. It was aiso proposed that monitoring could be dropped where monitoring experience had demonstrated the levels to be con strictive. There is no question that if they are promulgated as pro posed, they will place a very heavy burden on asbestos producers and users. Appropriate responses will be submitted by various segments of the asbestos industry and other interested parties. ` OSHA has stated in the Federal Register that the construction In dustry will not be covered by the newly proposed regulations. They will continue to operate under the present regulations until a new vertical standard for that industry is developed. This should not lead to a false sense or security, how ever. because the same medical conclusions on allowable exposure levels are applicable regardless of the industry where they occur. Al so. the OSHA health regulations are rapidly moving towards a fixed format that will embody all of the same basic concepts regardless of the substance being regulated. It should be noted that the develop ment of an asbestos standard for the construction industry is in prog ress and recommendations have been submitted to OSHA by the Advisory Committee for the Con struction Industry. PROPOSED OSHA REGULATIONS- CRYSTALLINE SILICA Asbestos products do not consti tute the only potential health haz ard for the drywail industry. Tape joint muds contain crystalline silica which has long been recog nized as the cause of a disabling lung disease called silicosis. The National Institute for Occupa tional Safety and Health (NlOSH) has prepared a Criteria Document relating to occupational exposure to crystalline silica and submitted it to OSHA on November 11,1974. A proposed silica regulation has been drafted by OSHA and was to have been published during Sep tember 1975. The pressure on OSHA to prepare other regulations has delayed this publication but it will undoubtedly appear in a few months. NlOSH recommended an allow able maximum exposure level to airborne crystalline silica of 50 micrograms per cubic meter of air (50ug/rvta). Medical examinations, extensive monitoring, record keep ing, signs, warning labels, and oth er provisions similar to the asbestos regulations were also recom mended. An action level o# one half the allowable exposure limit was also defined as a cutoff point below which the regulations would not apply. 7 f <^A regulationsINERT OR NUISANCE DUST Table C-3 of Section 1910-93 of the OSHA regulations as revised on June 7, 1972 lists the maximum allowable airborne concentrations of inert of nuisance dust as 5 miltl* grams/cubic meter (mg/M) in the respirable fraction and 15 mg/M* in the total dust. If a dust is below the allowable levels for asbestos and silica but above that for nut : sance dust the regulations have been violated. This regulation has , been le> widclv publicized than those for asbestos and silica but has been in effect for a number of years. It must also be considered when job-site dust conditions are examined. COMPOSITION OF TAPE JOINT COMPOUNDS joint mud, either dry in i^or already mixed in five-gallon containers, is-a well-known ma terial at the job site. Few appli cators realize, however, what goes into a mud and how carefully the ingredients must be balanced to , give the critical blend of properties necessary to make the mud work properly during application and i after it has dried. The ingredients in a typical ready-mix tape joint compound are listed below: COMPOSITION OF i TYPICAL READY-MIX TJC Percent by Weight Ingredient Wet Dry Basis Basis Water 31 -- Limestone 41 60 Mta^fend Clay) 16 # 7 23 10 isoestos 34 Miscellaneous 2 3 100 100 Looking at the dry basis, which represents the condition when the mud is cured, it can be seen that the principle ingredient is lime stone. This is the. bulk filler that keeps the cost of the product down. It does not impart any hand ling properties to the wet mud. The next largest ingredient is finely-ground mica which is in the form of tiny flat plates- These tend to form a loose structure in the wet mud and have an important bear ing on how the mud flows when trowelled and how it shrinks when it dries. The other mineral ingredient is asbestos. It is present at a level of 3-5% and performs the function of controlling shrinkage and crack ing when the mud dries. It is also very important to trowelling prop erties which allow the mud to form easily in thick sections and permits feathering of the wet edge. The most critical function of asbestos in most muds is to provide freezethaw stability. Muds which do not contain asbestos will generally be unusable after they have been frozen.. . The binder in ready-mix is usu ally vinyl acetate, while casein, starch, or a similar "glue" is used in the dry mixes, it cures to hold the compound rigid and firmly at tached to the wait. The miscellaneous ingredients include such items as additives, fungicides, surfactants, cellulosic thickeners, and proprietary mate rials. These are important ingredi ents but will not overcome the effects of an Improperly balanced blend of major components. A compounder who wishes to formulate a mud without asbestos will have to replace it with a ma terial that will impart similar prop erties. The mica can be Increased or some other fiber-like material, such as certain clays, may also be used. Additional cellulosic thick ener to give the necessary viscosity is also likely to be required. This Has a tendency to make the vis cosity unstable, i.e;, cortect at the plant when manufactured but either too high or too low when the mud arrives at the job site. The reformulation problem be comes much more complicated when silica is considered. Four dif ferent limestones commonly used in the manufacture of TIC have been analyzed for crystalline sili ca content and found to range from 0.3 to 2%. Similarly, three different micas had silica contents of 2, 5, and 9%. While asbestos is usually free of crystalline silica, days often contain substantial quantities. By proper selection of ingredi- . ents, it Is possible to produce a mud with a silica content as low as 0.3%. Unless the low silica ingredients are readily available mud costs will increase. Since silica appears everywhere In nature, it Is unlikely that a tape joint mud can be pre pared without detectable levels. If the proposed regulations are promulgated, workplace monitor ing can be extensive and a con siderable financial burden can be imposed on contractors. Eleven commercially available muds were found to contain from 0.3 to 2.5% of crystalline silica which is consistent with the silica content of the raw materials. Very few mud suppliers appear to be aware of the potential silica prob lem. It is well known that the major tape-joint compounders have had extensive research programs under way for the past several years to develop asbestos-freemuds that work as well as those with asbes tos. So far, the programs have had limited success. The muds devel oped are more expensive and gen erally do not perform as well. The formulations now in use evolved to their present high-performance level over many years and it is, ob viously, difficult to replace the key functional ingredient:'" r : (Continued on page 30) (Continued from page A ) ASBESTOS EXPOSURE IN THE TAPE JOINT INDUSTRY The tape joint industry had their attention drawn forcibly to the as bestos standard in the Spring of 1974. A group at Mt. Sinai Hospital, led by Dr. Selikoff, announced the results of a study of 59 tapers who well within the regulations. A pos sible reason for the difference can be found in the application and sanding conditions, i.e., hand-tool applied and heavily sanded in New York City compared with Ames tools and light sanding in Florida. The question of different work practices was pursued further with various contractors. It was found that the amount of sanding done varied widely, even within a geo graphical area. It depended on the way the mud was applied, i.e,. Ames vs. hand tools, the skill of the operator running the mud, the type of finishing coat to be applied to the wall,. the size and quality of the job. i.e., custom or "mass production," the amount of venti lation, and the personal preference of the contractor. In addition to these mechanical factors, different mud formulations appeared to vary widely in their tendency to gener ate dust when sanded. In general sanding was minimized to reduce costs. It was obvious that more infor mation from other parts of the country was needed to better de fine the levels of asbestos exposure to be expected. With the assistance of the GDCI and the excellent co operation of various individual contractors, field tests have now been run in New York. Texas, Michigan, and Minnesota. The New York, Michigan, and Minnesota I 1974, Drywall Tapers and Pointers ; of Creater New York. The fiber ) counts found during sanding were ; generally very high and one long time worker in the industry had a clearly recognizable case of lung fibrosis. The same data were trans mitted to NIOSH who issued an alert to the industry. At the time of this publicity, a major supplier of asbestos and oth er products to tape joint compound manufacturers had cojlected dust count samples during sanding at two locations in Florida. In con trast to the New York City results, the fiber levels found were IdW and' er as wide a range as possible in the "intensity" of the sanding op eration. Conditions varied from one man sanding lightly to three men sanding heavily in the same apartment. The New York tests al so provide information on hand tool application. In addition to as bestos tests, air samples were collected at several of the locations to check the airborne concentra tion of crystalline silica (quartz) in the respirable fraction of the dust. The results of these tests will be presented in the lanuary-February Issue- - , r.mr. Drvwall January/February 1976; 22:1-6 ASBESTOS AMD SILICA DUST In the Drvwall industry. ausIness-Health-Ufe Part 2 Harrison 8. Rhodes Technology Manager and Blair l- Ingalls Supervisor, Special Projects Union Carbide Corporation Metals Division Niagara Falls. New York , Introduction In the la*-t issue i >f the CDCl Drv- >v.ill Magazine, the current qhtuA ot the OSHA regulations for asbes tos and for crystalline silica wss described. This article completes the picture with field data on as* bestos and silica exposure under normal operating conditions ob tained at eight iob sites in four _atailes. Sanding, wet-out of dry-mix W" ttenerida.lt,Waonrkd cleanup were procedures at ex* the jobs tested are described so that the results can be related to simi lar operations in other locations. Abstract The concentrations of respirable The highest airborne asbestos dust generated by three different concentration found during sand dry sanding procedures varied by a ing was 1-5 fibers/cc longer than 5 factor of ten. The contractor has a micrometers. This is well below the great deal of control over dust allowable OSHA ceiling limit of 10 levels on the job by his choice of fibers/cc. The corresponding 8* work practices. hour, time-weighted average ex posures ranged from 0.2 to 0.9 fibers/cc. These levels are also well below the 5 fiber/cc limit now al lowed and the 2 fiber/cc limit scheduled to go into effect in mid 1976. Asbestos exposure during the wet-out of dry-mix materials ranged Exposure to airborne quartz was checked at five job sites and three were found to be near or above the Action level proposed by NIOSH. The observed levels depended di rectly on the quartz content of the mud and on the severity of the sanding operation. Much higher levels are possible under adverse from 2.7 to 62 fibers/cc. It appears combinations or these two factors. to be possible to hold the concen tration to acceptable levels by care The Choke for the Drywafl Industry handling of the hags but it is The information presented here tMbly desirable to wear an ap provides an excellent illustration proved respirator during tnis opof a broader question that is facing eration. industry today, i.e*. what is the best way to comply with the vari- . out occupational safety, consumer safety, and environmental protec* lion regulations that are being promulgated? These safety and health regulations are an estab lished trend of the times and ap pear to be here to stay. By their very nature, these regulations gen erally increase the cost of each product and service involved. Al though these costs will ultimately be borne by the final user, it bene fits everyone to achieve the appro priate level of safety and health In the most efficientway possible and thus minimize the incremental cost for these important items. When a new regulation is prom ulgated covering a particular ma terial. the natural reaction is to put the entire burden on the sup plier and demand that he replace V WW tew regulated ingredient. In the of asbestos, which imparts very valuable performance char acteristics to the tape joint com* pounds, the replacement is proving to be difficult. The asbestos-free muds so far available are more ex pensive. Also, they often do not trowel as well which adds to the. cost of installation. Additional re* formulation to reduce the quartz level could result in further loss in properties and increases in cost. It will be shown that the dust levels related to drywali finishing vary widely depending on how the contractor operates. This suggests that It may be to the contractor's advantage to make reasonable ad justments in operating procedures to use existing products in compli ance with regulations rather than demanding that the suppliers pro vide products that are completely safe under the most adverse job* conditions but are more ex* sive and do not perform as welt. Collection of Dust Samples The photographs on the cover of the November*December issue of Drywali Magazine showed how the air samples were collected. Both personal samples and high* volume area samples were ob* tained. For personal samples, a small battery-driven vacuum pump was hooked to the operator's belt. Acartridge containing a filter paper about one and one-half inches in diameter was attached to the oper* ator's shirt pocket and connected to the pump with plastic tubing. As the man went about his job In the normal manner, air from his breath* ing zone was dravyn through the filter paper by the vacuum pump so that the dust present In the air sample was deposited on the fil ter paper. The high-volume samplers operPtod the same way but were larger and pulled about five times as much air. They were mounted on poles adjacent to the sanding and were moved at regular intervals to stay close to the operator. There was one important differ ence in the samples collected for silica analysis. The proposed regu lations refer to the "respirable frac tion" of the total dust This fraction is made up of the smaller, lighter particles In the total dust which are considered most likely to be carried into the lungs during ' breathing. A small cyclone sepa rator was used ahead of the filter for these samples to remove the heavier dust particles and leave only the respirable dust. For the asbestos measurements, the filter paper was examined un der a microscope and the number of fibers longer than 5 micrometers (pm) was counted. For silica, the total quantity of sample collected was weighed and the percent quartz was found by X-ray diffraction. All procedures used were in accord ance with OSHA regulations for as bestos or NIOSH recommendations for crystalline silica.1 tti rm i TT ;n in 1a -- 8 \Z 1 SB LJj iiB t r i IbEEEBHB _ i. 111 1 mr ^ 1=11-1 ml li. i : 11:11 L. BP - a. i f ill-ill 7r i Ti 1 i ' 1 l(1 n 1! r ri i1' nr j r jg ii ! B ;:iiy 1i imt 5 f" E--r 1It *r BIB B p-JaX nai m i m-mwmmwm Airborne Asbestos Exposure in Drywali Finishing Sanding of Finished Joints: Air borne asbestos fiber concentra tions during routine sanding opera tions were measured at six loca tions in four states. The results are shown in Figure 1 together with the data reported by Nicholson et al*. The range of fiber concen tration measured at each location is given by the cross-hatched bars. The type of sanding, hand or pole, and the total number of personal samples taken at each job location are shown at the bottom of the Figure. It is immediately evident that the samples collected in this sur vey are much lower than those re ported by Nicholson. When this gross difference became evident two filters each from three differ ent locations were sent to inde pendent laboratories for check counts. The results are compared with, those of the Union Carbide laboratory in the following table: nteriaboratory Coaieartien AaboMot Fiber Counli Akbema Album fibor Conevt>iion (Hb*n/cc tongf tbm tfani . Sampl* fcvrca B, UCC by Lab A by tab 1 Location I (Filter *1) location 1 (Filter *2) Location II (Filter It) Location II (Filter *2) Location til (Filter *1) location m (niter o2) 0.4 04 IS 1.3 0.0 04 04 0.0 IP IP oo 02 02 04 1.0 0.0 0* 04 . Although there is some variation, these are difficult samples to count and the agreement between labora tories is excellent. It is evident that the differences between this sur vey and that of Nicholson are not. due to sample analysis. The sand ing procedures used to generate seem to be the most likely cause, in any case, the Nicholson results do not appear to be typical of the concentrations encountered under most job-site working conditions. 1 The authors wish to express their thanks to the NCC Environmental Laboratories. Cold Bond Building Products. Division of National Cypsum Company, Buffalo. New York, who provided the collection equip ment and analyzed the silica samples. * Paper presented by Of. W, Nichol son at the Miami, Florida meeting of the American Industrial Hygiene As sociation Conference. May 12-17, 1974. Ik ... .UL-26-'BB iL-.yy.. rN <>-* j^The ceiling limit allowed under >j^Be present OSHA asbestos regula tions is also indicated in Figure 1. This limit is the highest level to which a worker may be exposed at any time without protective equipment. It is evident that the asbestosconcentration in the seven )obs checked In this survey were all well below the 10 flbers/cc limit. The OSHA regulations also spe cify a maximum allowable time* weighted average exposure of 5 fibers/cc now and a reduced level of 2 fibers/cc in July 1976. The Time-Weighted Average (TWA) is a measureof the workers'average ex posure during the entire 8*hour workday. This concept if particu larly important to the tape joint industry where asbestos exposures generally occur only during a mod erate portion of some working days. As an example of Time-Weighted AnTvCertage, a man might sand for two ours at an exposure level of. 4 rs/ccand work at some other job ^Krxr t1 he rest of the shift at another location where there is no asbes tos present so the exposure would be essentially zero, in this case. his Time-Weighted Average would be calculated as: Hfiten/ctl X |1 konl n'feoVCtl X TM&i ti . j~i-- . ~ O M*) + (ft httrtl ~ WX^WXJM *1 Time-Weighted Average exp^ sures have been estimated in the manner shown above for the seven job operations in Figure 1- The re sults are listed in the following table: Mar CxMMln fiariiv Dn4* !** !**-* (w w.u m>tih H jTuaX. vlxXal*. n iWh * 14 M u 14 14 Ift iwfcii_iraw>>i>Bi 14 44 U44 14 10 as 11 M 0.1 u ft HM jThe estimated TWA values frige from 0.9 fiber/cc down to 0.1 fiber/cc. They are all well below the current 5 fiber limit and the July 1976 2 fiber/cc limit. While it is recognized that this is only a small sample from the hun dreds of locations throughout the country where tape joints are sanded, the sanding procedures used were typical of most commer cial situations. The results pro vide good, evidence that the as bestos concentrations during sand ing at most locations are generally below the allowable OSHA limits. . Wet-Our of Dry-Mix Materials: In some parts of the country, drymix tape joint compounds and tex ture sprays containing asbestos are widely used. When these are mixed into water at the job site, as bestos exposure can result. Spray texture paints may contain about the same level of chrysotile asbes tos as tape joint compounds. Asbestos exposure during the wet-out of wall and ceiling spray texture was measured at two loca tions. In Figure 2 the results are compared with those of Nicholson for the wet-out of tape joint com pounds. Since these are short-term occasional exposures, the ceiling limit of 10 fibers/cc is most perti nent and is also shown on the Fig ure. vary widely and are also frequently well above the 10 fiber/cc limit. In the San Jose test where the bags were emptied slowly and carefully, the levels were low. At the other location where the bags were emp tied rapidly and shaken in a closed truck the fiber concentrations were in the same range as the high levels reported by Nicholson, On the basis of this data, it is prudent to wear a respirator while wetting out dry-mix and the bags should also be handled with care. . Cleanup After lob Completion: Asbestos exposure may also occur during the cleanup after a drywall finishing job is completed. Limited data on this operation are shown in Figure 3, together with the re sults reported by Nicholson. In the left-hand portion of the figure are data obtained in a test at a Florida condominium. Both the walls and ceilings had been sanded lightly and then sprayed with tex ture paint. The texturing overspray had hardened on the floor. The normal cleanup procedure was to wet the floor lightly with water from a hand sprayer and then re move all excess material from the floor with a long-handled scraper. As might be expected, (his damp operation gave a very low airborne fiber concentration of 0.3 fiber/cc. In order to get a direct compari son with other cleanup methods, a number of apartments In the same building were swept with a stiff broom, both with and without the addition of ordinary sweeping compound. It was difficult to break loose the hardened overspray so the broom work was fairly vigorous. In spite of this, the highest level f- jUu'ibr ' au vv*ij> sV tins ... '^Jfnd was a ceiling concentration of 5.5 fibers/cc produced by the dry sweeping. Use of the sweep* mg compound reduced this to 1.8 fibers/cc. 1 These data illustrate that moist scraping, which is now in regular commercial use In some parts of the country, is a good cleanup method to control dust. These data do not mean there is no asbestos dust problem during cleanup since jobs where the walls have been sanded heavily present more po tential for dust generation than the light sanding case tested. This point is emphasized by the data of Nicholson in Figure 3 which gave levels of 26 and 43 fibers/cc during sweeping after heavy sanding. While it seems doubtful that levels this high would be encountered in most typical job cleanup situa tions, exposures above the ceiling Kimit appear quite possible. More nformation is needed to define better the levels to be expected . under routine field conditions. Airborne Respirable Dust Exposure in Orywall Sanding It was noted in the first article that there Is an OSHA standard which sets the maximum allowable exposure level to the respirable fraction of nuisance dust at 5 milli grams per cubic meter (mg/M1) of air. In simplest terms, a nuisance dust is a dust which does not have the exposure level controlled by any of the other standards for spe cific materials. Even if a dust con taining asbestos and/or crystalline silica It in compliance with the standards for these materials, it would still be in violation if the respirable dust level exceeds 5 mg/M*. The concentration of respirable dust during sanding was measured at five of the job sites in three states. These levels, expressed as milligrams of respirable dust per cubic meter of air, are shown in Figure 4. The crosshatched bar* give the range of concentrations found at each job with the respec tive average concentrations shown by the dark line in the central por tion of each bar. Sanding condi tions for each site are also noted. At the New York location, two courses of general-purpose, readymix mud had been applied with hand tools. The building was a high-rise apan mem with the win dows open and a light breeze blow ing. A five-man crew of tapers was spot sanding lightly by hand or with a pole sender as needed and touching up with a finish coat of general-purpose, ready-mix. Usu ally only one man was working in each room. Respirable dust levels from personal samplers ranged from 0.2 to 1 milligram per cubic meter and averaged a very tow 0.55 mg/M*. The Michigan test took place at a multilevel dwelling (approximate* ly 2.300 square feet floor area) fin ished with a dry-mix topping com pound. The windows were closed and there was no ventilation. A laborer, who normally spends most of his time sanding, went over the walls and ceiling in about four hours with a pole sander. Respir able dust ranged from 1.55 to 5.34 mg/M* and averaged 3.02 mg/M1. The tests at Minnesota Site 1 and Site 3 were quite similar to that in Michigan. Both were residential dwellings of 2500 and 1500 square feet, respectively, finished by hand tools with asbestos-free dry-mix topping compound and pole sanded in about four hours by a laborer who did this as a full-time job. The windows were in and there was little ventilation. At the small er house. Site 3, only the walls were sanded. Respirable dust at Site 1 ringed from 0.15 to 3.23 mg/M1 and averaged 1.45 mg/M*. At Site 3 the range was narrower at 1.59 to 2.62 mg/M1 but averaged about the same at 2.10 mg/M1. Minnesota Site 2. was a fourstory apartment buiiding with an asbestos-free dry-mix topping com pound finished with hand tools. There was very limited ventilation while three men sanded together in each apartment unit until It was finished and then moved on to the next unit. Here the range fell in the much higher level of 4.06 to 7.95 mg/M1 and the average was 5;76 mg/M1. This was the only lo cation where the respirable dust level consistently exceeded the OSHA limit. These data show clearly that there can be a very wide, tenfold, difference in the average respirable dust levels for the different seven ities of sanding. Light touch-up sanding with good ventilation gave about 0.5 mg/M1. The three tests with one man sanding steadily with little ventilation ranged from 1.S to 3 mg/M* and averaged 2.1 mg/M1; about four times that for touch-up. Three men sanding to gether increased the average level to about 2.5 times that of one man sanding alone and 10 times that of touch-up. It is very dear that the dust level at the job site can be changed widely by the work prac tices employed. Airborne Crystalline Silica (Quant) Exposure In Orywall Sanding The airborne quartz concentra tion in the dust generated during thesandingof tape joint compound was measured at five job sites in three states. The concentrations (Continued oh psie 30) / (Continued from page 11) fc^feexpressed in micrograms per CiSPneter, are shown in Figure 5. A microgram (ug) is 1/1000 of a milligram so these levels are much tower than the respirable dust. The maximum allowable TWA and Ac tion Level proposed by NIOSH, the quartz content of each mud, and the average level of respirable dust measured at each job location are, also given. #r " - - - gr . wo locations, Minnesota Sites 2 and 3, had quartz concentra tions that were above the pro* posed action level, and a third, Michigan, approached this level. The other two jobs tested. New York and Minnesota Site 1 had very low quartz levels and were well below the Action Level. Three out of five of these job sites thus had concentrations high enough so that regular monitoring would probably be required under the proposed reg ulations. The results for Minnesota Site 2 are of particular significance- Here three men sanded together in each apartment and generated the high est observed respirable dust level of 5.66 mg/MJ but the quartz level was not the highest found by a con siderable margin. The mud being sanded had a low quartz content sotl^ dust generated also contiV less quartz. -This point is shown mo/e spe cifically by a direct comparison of the New York and Minnesota Site 2 results.The mud used in New York contained about three times as much quartz as that used in Minne sota. The sanding was lighter in New York, however, and only about one third as much dust was gen erated. These opposing factors bal anced out to give the same quartz level at both locations. A mud with a high-quartz level, sanded lightly, can thus give the same airborne quartz concentration as a lowquartz mud sanded heavily. The broader applicability of this principle is Illustrated in figure 6 which compares the concentration of quartz in the respirable dust with the concentration of quartz in the mud being sanded. Over the range of mud concentrations tested, these two concentrations are approximately equal. On this basis, a mud containing 2.5% quartz sanded at the most severe conditions like Minnesota Site 2 could give a quartz concentration around lOOpg/M', far above the allowable level. It was shown in the first article that the eleven commercial muds tested had quartz levels ranging from 0.3 to 2.5%. The tape joint industry thus appears to be facing a range of conditions. Light sand ing of iow, and even medium, sili ca muds should give quartz con centrations well below the pro posed Action Level. Heavy sanding of high-quartz muds is likely to give concentrations well over the allowable limit. The whole range of quartz concentration in between it possible depending on the kind of mud used and the sanding pro cedures followed. Summary and Conclusions The exposure to airborne asbes tos during the sanding of tape joint compound was measured under routineworking conditions at seven job sites in four states. A wide vari ety of sanding conditions was tested. Exposure to respirable dust and crystalline silica (quartz) was also measured at most of these sites. The airborne asbestos ceiling concentration found at' each of the sites ranged from 0.4 to 3.6 fibers/cc longer than 5 micrometers compared with an allowable level of 10 fibers/cc longer than 5 mi crometers. Time-Weighted Average . exposures were also calculated for each job and were found to vary from 0.2 to 0.9 fibers/cc longer than 5 micrometers. These levels are well below both the OSHA limit of S fibers/cc now allowed and the 2 fibers/cc level sched uled to go into effect in mid 1976. Asbestos exposure, during the wet-out of dry-mix tape joint com pounds and spray-texture paint was examined. Ceiling exposures for this short-duration operation ranged from 2.7 to 62 fibers/cc longer than 5 micrometers. It is possible to keep the concentra tions at acceptable levels by care ful handling of the bags, but it is probably desirable and may be nec essary to wear an approved respir ator during this operation. The sub stitution of ready-mix is also an obvious possibility. Cleanup procedures after core pletion of drywall operations were tested briefly. Both high and low asbestos dust levels appear to be possible, depending on the amount and type of sanding done and the type of sweeping. A very effective wet-spray and scraping cleanup method now in general use in some part) of the country was demon strated. The concentrations of respirable dust generated by light touch-up sanding, by continuous sanding by one man, and by continuous sand ing by three men were compared and found to vary by a factor of about ten. The highest concentra tions found were above the OSHA limit for nuisance dust. The quartz content of eleven commercial muds was found to vary from 0.3 to 2.5%. The quartz content of the common raw ma terials used in the manufacture of tape joint compounds suggests that a completely quartz-free mud may be difficult to attain. Exposure to airborne sanding dust containing crystalline silica (quartz) was found to range from 2 to 47 micrograms of quartz per cubic meter of air sampled. Three of the five locations tested gave levels above or close to the NiOSH proposed Action Level of 25 micro grams per cubic meter. The air borne quartz level depended di rectly on the quartz content of the mud and on the severity of sand ing. It could be much higher than 47mg/M1 under readily attainable conditions. At these levels, the pro posed OSHA regulations on crystal line silica would require monitor ing and other precautions similar to the present asbestos regulations.