Document 6RByQx5Y3VQmjexXRjabdQ5Bd

FILE NAME: Visible Dust (VDT) DATE: 2002 DOC#: VDT020 DOCUMENT DESCRIPTION: Journal Article Applied Occupiam gl wx! Smiionnuaitl Hygistit \Wame 170): 55-60. 20(70 Copyrigit 2002 Applied InAuliial Hygiene IQ47-322G2 *12.00+ .00 Fiber Release During the Removal of Asbestos-Containing Gaskets: A Work Practice Simulation William . Longo, William B. Egciand, Richard L. Hatfield, and Larry R. Newton Materials Analytical Services, Inc., Stavanee, Georgia Work pFsetjes s t a t e were conducted Involving the removal at astastee-contalnine sheet gmkm, fr o m SUM m Ranges. These studied were parfarared bo determine potential exposure levels to individuals wbn hue* worked with these types of ssaterlals is the pan and may still work with these products today. The work practices wen: coudacted Inside an exposure eharueterixation laboratory (ECL) and w e n perforated by scraping- and w in brush ing, chrysotlle-coiolaizririg (65% la 85%) sheet gaskets from a m aster o f nsed steam flanges. Airborne asbestos lends w en menaored by phase contrast microscopy (PCM) nod tnuassofeslon electron m lcraaapy (TEM) far the person nel and a n a a ir unplea collected during the study. These workplace m utations showed substantialasbestos fiber lease using scraping, hand wire brushing, and power wire brushing techniques during the gasket removal process. The range of concentration was 2.1 to 31,0 fiberafee greater than 5 micrometers when measured by PCM. These results con trasted with the few reported results in the published liter ature where low er airborne asbestos levels were reported. In these studies the airborne asbestos fiber levels measured In many of the samples exceeded all current and histori cal Occupational Safety and Health Administration (OSHA) excursion lim its (15-30 minutes) and some previous perotiaible exposure lim its (PEL) based on eight-hoar timeweighted average (TWA) standards. Also, individuals who performed this type o f work in the past may have had expo sures higher than previously suspected. The results demon strated that em ployees who remove dry asbestos-containing gaskets with no localized ventilation should wear a full face supplied air respirator with a H EFA escape canister and the work area should be designated a regulated area. Keywords Asbestos, Gsskc. Rarnoval, Exposure Asbestos-containing sheet gaskets have been used in almost every type o f industry for the last <50 y ean . These Bankers taxi the ability to prevent leakage between different types of cou plings, particularly at elevated temperature and pressure/1*There types of gaskets stonasHy contained 70 percent to 50 percent chrysattie asbestos by weight (a some cases erocidolite asbestos was used for special applications, that is, sealing flanges In add lines. The remaining non-asbestos component of the gasket was usually constructed of synthetic rubber material that consisted of cither neoprene, styrene butadiene rubber (SBR), o r a nitrile polymer, ,>~*i Most companies replaced asbestos libers in their gasket prod ucts with other nonmineral fibers in the late 1980s or early 1990s. This coincided with the Environmental Protection Agency's (EPA) 1989 ban on the manufacture, importation, pro cessing, and distribution of these types of products.<5) However, the United States Fifth Circuit Court of Appeals vacated most of tba asbestos ban and Phase Out Rale godremanded it back to EPA in October 1991. Although the court vacated and remanded moat of the rule, it left intact the portion that regulated asbestos products that were not being manufactured, produced, or im ported when tbe rule was published in December 1989. Since asbestos-egnuirung she gaskets were still boios imported into this country, they were exempt from tbe ban and can still be manufactured, purchased, and used in the United Statoi, Fowler recently described the problem with tbe use of these products when be demonstrated that the application of asbestoscantaiaing gMkeu had toe potential to release respirable asbestos fibers well above current OSHA standards. Fowler rec ommended that these products should not be used in today' industry and that only non-asbesto gaskets should be used in their p la c e d An issue that faces many former industrial workers is toe pa*' use of these types of gaskets, 'Workers were not informed in most cases that the products they were using had the poten tial to release elevated levels of respirable betters fibers. Lego) issue* concerning past exposures pose this basic question: Did handling and performing maintenance activities on these gaskets contribute to their asbestos exposure history? Industrial hygien ist m w t rely to a retrospective exposure assessment to make 83 " e x h i b i t 55 'jg & d u d & k -- < 2 . 1 56 W. E. LONGO ET AL. this d e te r m i n a ti o n .I n this approach the individual's w ork h is tory is com pared to the results of retrospective exposure assess m ent studies that replicate their work activities. A review o f the peer-reviewed literature found very few pub lished studies involving exposure assessments during the dry removal o f asbestos sheet gaskets from flanges.*7-95 T he stud ies o f Cheng, M illette, and M cKinery were somewhat lim ited in the inform ation reported. M illette used only a small num ber o f flanges. C h en g 's w ork did not verify that all the gaskets contained asbestos. Additionally, there was only limited infor mation provided in all three studies concerning the size and the history o f the flanges used or the length of time requited for the gasket removal process. T he m ost com prehensive study to date was by Spence et al,*105 However, the authors used w ening to control the airborne release of asbestos fibers. T his lim ited the study's value for any retro spective exposure assessm ent since dust control methods were not used in the w orkplace historically. La contrast to the previous studies, the goal o f these new w ork practice studies w as to estim ate a w orker's asbestos fiber exposure during the rem oval of asbestos-containing sheet gas kets using com m on rem oval techniques such as scraping, hand wire brushing, and pow er w ire brushing. The studies were con ducted on a large population o f steam line flanges and valve assemblies. The com pilation o f several studies discussed in tins article allows a m ore accurate retrospective exposure assessment for individuals who worked with these products in the past and the assessm ent o f potential exposure to workers w ho may be rem oving asbestos-containing gaskets today using these sam e work practices. High-intensity lighting and videotaping techniques were used inside an exposure characterization laboratory (ECL) during the work practice studies to visually document the pathway of ex posure during f te gasket removal process and to help determine what activities produce the airborne asbestos d u st The methods and procedures described in this report can be applied to assessing past and present industrial hygiene expo sures to other dusts, fum es, and fibers besides asbestos. The videotaping o f dust, fume, and fiber exposures under highintensity light can be used as a training tool in visualizing the im portance and effectiveness of engineering and administrative controls and respiratory protection. MATERIALS A ND M ETH O D S A num ber o f valve and flange assemblies were collected in 1994 from a p ap er m ill pow erhouse in Oregon and stored under am bient conditions in a protective environment until their u se in these studies. A sam pling o f these flange and valve assemblies was partially opened to confirm the presence of asbestos in the sheet gaskets using polarized light microscopy (PL M ) prior to the w ork practice study.1'*) A ny opened flanges w ere reassem bled and theoucside surfaces o f all the flanges w ere cleaned, sand blasted, and repainted. Interviews with former machinists and pipefitters determined that the m ost comm on techniques fo r re moving gasket material tightly adhered to the flange surface w ere hand scraping, hand w ire brushing, and/or electric wire brushing. The work practice simulations w ere conducted inside an ex posure characterization laboratory (ECL) that was constructed as a containment area to prevent the release o f asbestos to the outside environment. The dim ensions o f this containm ent area were 6.0 m (length) x 4.5 m (w idth) x 2.4 m (height). T he ECL also contained two viewing ports for videotaping purposes and had a decontamination area for contam inated clothing disposal, an air lock for sample removal, and showers to further control fugitive emissions. Fresh air was produced by a high efficiency particulate ab solute (HEPA) filtered negative air m achine manufactured by Aramsco (model #55011) and pulled through the ECL at a venti lation rate o f 5.7 cubic meters per minute. This unit was operated at an air exchange rate o f five times per hour (ACH) during the work practice studies. The air in t i e chamber was flashed be tween studies by increasing the fresh air ventilation to 28.3 cubic meters per minute for a minimum of 24 hours. At the end o f the first scraping and hand w ire brushing study (Study 1), the E C L was completely decontaminated by HEPA vacuuming all dust and debris and then w et w iping. A lso, all inside surfaces w ere repainted after the decontam ination procedure. High-intensity lighting (700-1000 watts) was ased inside the cham ber during videotaping of the work practice to document dust generated by various tasks and to observe pathways of ex posure to respirable d u st In previous studies the use o f highintensity lighting was found to be an effective tool to display respirable airborne dust released from asbestos-containing prod ucts during work activities.*12,135 T h e authors performed these studies wearing norma] work clothes over disposable protective suits and w ere equipped with supplied air respiratory protection w ith HEPA escape filters. Personal and area air sam ples w ere collected during ti e studies using nonconducuve three-piece cassettes. The cas settes contained m ixed cellulose ester (M CE) filters that were 25 m illim eters in diam eter and had a 0.8 m icrom eter pore size. These filters rested on a M CE backing filler (5.0 micrometer pores). The personal and area air sampling pumps were cali brated before and after the completion of each study against a DryCal primary flow meter to air flow rates of two and ten liters per minute, respectively. High-volume air-sampling pum ps (Dawson 110 volt) w ere used for collecting area air sam ples dur ing tie studies. Four area sam ples were located in four equidis tant quadrants at a distance of 2.1 m eters from a work bench placed in the center o f tie ECL. T he area sam ple cassettes were placed on sampling stands at a height o f )_5 metere. T he four calibrated high-volume air sam pling pum ps w ere placed outside the cham ber and each pump was connected to an area air cassette by Tygon tubing passing through die wall of t i e ECL. T he tw o investigators perform ing the studies were each fitted w ith tw o calibrated personal G ilA ir air sam pling pumps with the air-sampling cassettes attached to each shoulder and within their FIBER RELEASE DURING REMOVAL OF ASBESTOS 57 breathing zones. Background area sam ples w ere collected inside and outside the E C L before each study. The air samples were collected in genera] accordance with the NIQSH 7400 method entitled, "Asbestos and Other Fibers by T\vd air sam pling cassettes w ere opened for 30 seconds inside the EC L to serve as personal field blanks at the end o f each study. Surface morphology of new and used gasket material was examined using a Hitachi 5-800 field em ission scanning electros microscope (SEM). Photom icrographs were taken of the gasket surfaces to docum ent the degree o f gasket degradation and the relative amount o f asbestos fibers present on the surface. S tu d y 1-- S cra p in g a n d H a n d W ire B ru sh in g o f Small Flange Assemblies Seven small Range assemblies w ere used in this study. The gaskets had outside diameters of approximately 69 mm and working widths o f approximately IS mm. Gaskets were removed from one flange on th e first fo u r valve assem blies and then from two flanges on each side of the rem aining three valve assemblies fo r a total of ten gaskets. T he flange assem blies w ere first opened and then the gaskets w ere scraped using a stiff, four-inch-wide putty knife. Any residual gasket material that could not be re moved from the flange faces by scraping was removed by hand wire brushing. Some o f the gaskets required repetitive scraping and wire brushing to remove the gasket and to polish the flange face. The sheet gaskets were removed sequentially from each of the 10 flanges. O ne o f the investigators in th e E C L sim ulated the worker who did all of the gasket removal while die other acted as a "helper." T h e helper changed th e area and personal air sample cassettes periodically throughout the study. Each gasket was collected and retained for analysis to determ ine both asbestos content and m atrix identification after removal. T h e investigators were-in the E C L for 194 m inutes. All air sam ple cassettes in the E C L were exchanged every 15 to 30 minutes. A total o f seven sets of air sam ples were collected. Study 2-- Scraping an d H and W ire Brushing of Large Flange Assemblies Four large flange assemblies w ere used for this study. The outside diaineier o f these gaskets varied from 125 mm to 200 mm and the gaskets were 19 mm to 25 m m w ide. T he gaskets were rem oved and collected from the four flanges as described in S tudy 1. T he investigators were in ihe E C L fo r 113 minutes. A ll a ir sam ple cassettes in the E C L w ere exchanged every 15 to 30 m inutes. A total o f five sets c f air sam ples w ere taken during this work practice siraulatkm. S tu d y 3---P o w e r W ire B ru sh in g o f L arge F lan g e A ssem bly A n electric wire brush (Skil electric drill 0.3 Hp with a Colum bian 10.2 cm crimped w ire w heel) was used during this study to rem ove gasket residue that could not be removed during the scraping and hand wire brushing of the first flange assembly used in Study 2. T he electric wire brush was also used to polish the flange face surfaces, This study was conducted one day after Study 2, T he E C L was not decontaminated betw een the stud ies. The tw o flange surfaces w ere electric wire brushed un til the gasket resid u e w as visibly removed. As previously d escrib ed in Study 1. th e tw o investigators -were in the E C L p e rfo rm in g the study. One person did the removal work while the other assisted as the helper. T he residual gasket material w asnot retained since the bulk a f the m aterial was collected in Study 2. T he investigators were in th e E C L for 42 minutes. The air cassettes in the E C L w ere exchanged every 10 minutes. A total o f fo u r sets o f air samples w ere taken during the electric wire brushing activity. All air filters collected were analyzed by PCM in general ac cordance w ith th e N IO SH 7400 m ethod using the "A " counting rules. A dditionally, all air samples were prepared fo r IB M ex am ination usin g th e indirect preparation m e th o d /15*T ne in d irect TEM preparation method was chosen because filter overloading rendered the sam ples unsuitable for direct preparation despite frequent changing o f the air sample cassettes. A lso, the indirect TEM preparation m ethod enabled data comparisons to other published and unpublished studies previously perform ed that also used th e in d irect TEM m e th o d /1'* ''8* The T E M a ir sam ples w ere th en an alyzed by a modified EPA Level II p r o to c o l/19* Cloth sw atches from the work clothing worn by the investiga tors during the studies were analyzed by the recom m ended EPA m e th o d .^ Surface dust samples were collected from the w ork table after each gasket removal study and analyzed according to the A STM p ro to c o l/151 Background samples from the clo th in g and the w ork table surface were also collected before each study was started. T he rem oved gaskets were analyzed for asbestos type and c o n ten t by the standard PLM m eth o d /11* RESULTS It was determ ined by PLM that the gaskets rem oved in these studies contained 65 percent to 85 percent chrysotile asbestos (Table I). Table n and Table EQ, respectively, illustrate the P C M and TEM resu lts fo r Study 1. T he worker in Study 1 had a peak exposure level o f 10.1 fibers per cubic centimeter (f/cc) and an 8-hour TW A exposure of 1.5 f/cc. The area air sam ples w ere voided after the com pletion o f Study 1 when it was determ ined that the air-sam pling lines into the ECL were obstructed. T he Studies Study 1 Study 2 Study 3 TABLE I P L M analysis of removed gaskets Number of gaskets analyzed Asbestos type Concentration of asbestos in volume percent 50 Chrysotile 65-80% 4 Chrysotile 75-85% 1 Chrysotile 85% 58 W. E. LONGO ET A L TABLE II Study 1-- Scraping and hand wire brushing: small flanges. PC M airborne exposure levels (fibers greater than 5 m icrom eters) Sample type No. o f air samples analyzed Range (f/cc) Sample time weighed average (f/cc) B -hrT W A (f/cc) Background 4 0.0 0.0 N/A W orker 14 1.5-10.1 3.7 1.5 Assistant 14 1.2-4.2 2.4 1.0 Area samples* 36 -- -- -- Total air-sampling tim e= 194 minutes. *Tbe air-sampling lines into the ECL were obstructed, voiding the area air samples in this study. results for Study 2 are show n in Tables IV and V. The worker in this study had a peak exposure level of 24.0 f/cc and an 8-hour TW A o f 3.6 f/cc. Table V I and Table VIE list results for Study 3. T h e peak exposure level found while pow er wire brushing was 31.0 f/cc and the calculated 8-hour TWA was 2,3 f/cc. T he results for the surface dust samples taken from the w ork table and the fabric sam ples are shown in Table VIH. All PC M and T EM data in the tables are expressed for compar ison purposes as fibers per cubic centim eter (f/cc) greater than 5.0 m icrom eters in length. D IS C U S S IO N The asbestos concentrations measured in these studies were higher on average than other previously published studies for sim ilar work, practices.*7-95 i t is believed that th e hi gher concen trations found in these studies w ere due largely to the gaskets adhering m ore tightly to the flanges. Tightly adhered gaskets require higher energy for rem oval. As described by Fowler, the friability o f the product is alw ays relative to the energy ap p lied /6* Only rwo o f the fourteen gaskets removed could have been de scribed as easily detached. T he other tw elve required extensive effort o n one o r both of the flange faces. M achinists, pipefit ters, steam fitters, and others commonly described sheet gaskets as tightly ad h erin g to flange surfaces and requiring substantial work to rem ove the gasket material. Unfortunately, the various conditions and th e amount o f adhesion o f the gaskets in th e pre viously p u b lish ed studies w ere not reported.*7-95 'The adhesion o f g ask et m aterials generally has been related to its length in TABLE m Study 1-- S craping and h an d w ire brushing: sm all flanges. TEM airborne exposure levels (asbestos fibers greater than 5 micrometers) Sample type Background Worker A ssistan t No. o f air samples analyzed 4 . 14 14 Range (fibers/cc) 0.0 29.9-144.2 2.2-29,5 Total air-sam p lin g tim e = 194 m inutes. service and the conditions o f service such as tem perature and pressure. T he high tem perature steam flanges used in this study were from a steam powerhouse that operated for a number of years. The last stearrrfitter who maintained the steam system in dicated that gasket replacement was rare due to infrequent plant dow ntim e and few leaks. Gaskets that could be easily removed would not be expected to produce airborne levels comparable to w hat w as fo u n d in these studies. N ode o f the previous studies described the level o f difficulty of removing the gaskets from the flange surfaces. The air sam ples collected were analyzed by both PCM and TEM during the gasket rem oval activities in th e se studies. The two basic types of sample preparation for TEM air analysts are th e d irect an d indirect m e th o d s/15-'6,71" 235 S om e scientists have suggested that the indirect sample preparation method, particu larly the sonicatioD step, causes large complex asbestos struc tures such as fiber bundles and clusters to break up and bias fiber counts to higher concentrations.tI4,2S) However, studies per formed by the EPA and others have shown that this criticism is not valid and that the indirect technique is an acceptable method to analyze overloaded air samples.*26-285 The overloading o f other particulates on an air filter will ob scure fibers that are collected. This condition can lead to the undercounting of asbestos fibers if a direct preparation method is used. Controlling the particulate loading on a filter can be dif ficult when the disturbance o f materials generates large amounts of both fibrous and nonfibrous airborne particulates. The gen eral approach to reduce o r elim inate overloading conditions is to alter flow rates and sam pling times. However, paniculate load ing can be controlled by using the indirect preparation method without comprom ising sam pling times. The overloading prob lem can also affect the direct examination o f air filter samples by P C M (N IO SH 7400 m ethod). This was noted in Study 1, T he asbestos air concentrations measured by PCM in Study 1 decreased as the study progressed. This would n o t be consistent with the continued activities that took place inside the E C L dur ing the study. This effect was due to paniculate overloading on the filters. However, according to the TEM d a ta from Study 1, the asbestos fiber concentrations tended to increase as the work progressed. The sam pling times for Studies 2 and 3 were reduced in an effo rt to m inim ize overloading on the P C M air sam ples. FIBER RELEASE DURINO REMOVAL OF ASBESTOS 59 TABLE IV Study 2-- Scraping and h an d w ire brushing: large flanges. P C M airborne exposure levels (fibers greater than 5 micrometers) Sam ple type No. of air samples analyzed Range (free) Sample time-weighted average (free) Background 4 0.0 0.0 W orker 10 9.3-24.0 15.3 Assistant 10 5JZ-5J 8.8 Area samplesA 24 2.1-8.4 -- Total air-sampling urns = 1 1 3 minutes. *TWA not calculated for area or "bystander" samples. 8-hrTW A (f/ce) N/A 3.6 2.0 -- However, any fu rth er reduction in the sampling tim e w ould have had an im pact on the work activities. Therefore, the air-sampling tim es w ere not decreased any further, The current OSHA asbestos exposure standards are based on ftie N IO SH 7 400 method. This method measures only fibers longer than 5 m icrom eters in length and greater than 0.25 m icrom eters is width. However, these fiber dim ensions w ere not im plem ented by O SHA with regard to health issues. T he m inim um dim en sio n s w ere im plem ented solely d u e to the fiber resolution lim itations o f the PCM technique.I29' OSHA has long recognized that PCM is not fiber-specific or able to resolve fibers that are less than 0.25 micrometers in w idth. The TEM analysis perform ed in these studies augmented the PCM measurem ents by obtaining m ore complete and accurate mea surements o f the airborne asbestos concentrations. A com parison o f the air data collected from the PCM and TEM analyses showed fiber concentrations approximately 30 times greater in the TEM analysis. The differences between TEM and PCM m easurem ents have been recognized by others and are prim arily due to the resolution limitations o f the opti cal m ic ro sc o p e /30-31' T h e deficiencies o f PCM m easurem ents are especially acute when products such as sheet gasket m ate rials that contain high percentages of chrysotile fibers are the source o f the airborne fibers. It has been shown that free res pirable chrysotile fibers aie released when asbestos-containing products are abrad ed in som e m anner/6' W ork by the E PA demonstrated that single chrysotile fibers have an average diam eter o f between 0.03 and 0.07 m icro- TABLE V Scraping and han d brushing: large flanges. TEM airborne exposure levels (asbestos fibers greater than 5 micrometers) Sample type Background W orker A ssistant Area samples No. o f air samples analyzed 4 14 14 ' 24 Range (fibers/cc) 0.0 199.6-842.7 13.6-101.0 3.3-108.8 Total air-sam pling tim e -- 113 minutes. m eters.02' This average diam eter is approximately five times below the resolution of a phase contrast microscope. Therefore, single chiysotile fibers cannot be seen or counted using the PCM method, irrespective o f their lengths. Because of the inherent errors in PCM analysis, it w as suggested by the director o f the Health Effects Institute for A sbestos Research that OSHA should consider changing to TEM air sam ple analyses for occupational workplace compliance to adequately protect workers' health.03' An SEM examination o f th e sheet gaskets was performed to better understand the relationship between the physical activity o f removal and the m easured asbestos air levels found in this study. Generally, sheet gaskecs are comprised of approximately 70 percent chrysotile asbestos bundles in a synthetic rubber ma trix, T he SEM m icrograph (F igure 1) shows large bundles of asbestos protruding from the matrix o f new sheet gasket ma terial. Any m inim al disturbance or abrasion o f these bundles cars release asbestos fibers in to the air. A nother problem with asbestos gaskets is that the synthetic robber matrix begins to de teriorate after installation. In m ost eases installed sheet gaskets are subjected to high tem perature and pressure that will increase the rate o f thermal decom position o f the rubber matrix. This pro duces cross-linking o f the polym er molecules. The cross-linking process increases the gasket m aterial's friability by causing the n ib b er matrix to degrade and b eco m e b rittle/3*' A comparison o f die su rface o f a new gasket (Figure 1) to that of a used gasket rem oved from one o f tbs flanges in Study 2 (Figure 2) demonstrates bow the rubber matrix material is de graded. This degradation provides m ore opportunity for the re lease of asbestos fibers during ihe removal process. The fiber concentrations m easured in S tu d y 2 w ere higher than those mea sured in Study 1 even (hough m ore gaskets w ere removed in the first study. Factors b elieved to lead to these results w ere as follows: (1) The total gasket surface area removed in Study 2 w as much larger than in Study 1, (2) The gaskets in Study 2 were observed to be m ore friable and more deteriorated, and (3) All .the gaskets in Study 2 tore apart and remained adhered or attached to both of the flange faces when the flanges were opened. An electric powered drill equipped with a wire brush was used to remove some residual gasket material from two flange faces in Study 3. The resulting exposures during the work activities 60 W. E. LONGO ET AL. TABLE VI Study 3-- Pow er w ire bm shing. P C M airb o rn e exposure levels (fibers greater than 5 micrometers) Sample type No. of air samples analysed Range (f/cc) Sam ple time-weighted average (f/cc) Background 4 0,09-0.12 0.11 W orker 7 14.9-31.0 21.8 A ssistant 8 12.8-21.2 15.9 Area samples* 16 7.6-15.7 -- Total air-sampling time = 42 minutes. ATWA not calculated for area or "bystander" samples. 8-hrTW A (f/cc) N /A 2.3 2.0 -- were higher even though the residual gasket material was far less than the gasket m aterials rem oved in Study 1 and Study 2. It was observed in Study 3 that the mechanical action gener ated from tbe pow er w ire b rush to re loose more asbestos fibers and propelled them greater distances into the air. This observa tion supported the higher asbestos air concentrations o f the area sam ples m easured in S tu d y 3 co m p ared to those measured in Study 2. The results fro m the surface dust and fabric samples (Table VKI) showed that the surface asbestos levels measured can be classified as "highly contaminated" and pose additional exposure problem s to the w orker throughout the workday. Addi tional asbestos exposure can o c c u r to both Che w orker and other family members if tits clothes are worn away from the job or taker. h o m c .^ CONCLUSIONS AND RECOMMENDATIONS These studies, as well as the o ther studies previously dis cussed, demonstrate that there can b e w ide variability in airborne asbestos fiber levels generated during the removal o f asbestoscontaining gaskets from flanges. T h e variability o f fiber levels released is most likely d ep en d en t o n the condition o f the asbestos g ask et the size o f the gasket surface area and the method of re moval. The condition to w hich a gasket is subjected determines the degree of adhesion o f the gasket to tbe flange surface and the friability o f the g ask et T h is im pacts the amount o f energy required to remove the gasket and release asbestos fibers. The determ ining factors that seem to affect the condition of the gasket TABLE VII Study 3--Power wire brushing. TEM airborne exposure levels (asbestos fibers g reater than 5 micrometers) Sample type No. o f air sam ples analyzed Range-fibers/cc Background 4 0.0-0.2 W orker 7 877.1-1636.1 A ssistant 8 60,4-364.4 Area samples 16 56.9-801.9 Total air-sam pling tim e = 42 m inutes. are: length of service, temperature and pressure conditions, and com position of the gasket matrix. O ur data show that dry removal m ethods typically used by m achinists and pipefitters (past and present) resu lt in significant airborne asbestos fiber exposures. For retrospective asbestos ex posure assessments, the exposures m easured by PCM in Studies 1 ,2 , and 3 exceed aJI historical OSHA ex cu rsio n lim its and som e previous perm issible exposure limits (PEL) based on an eighth o u r TW A. The. exposures also far exceed c u rre n t OSHA levels. T herefore, former machinists and pipefitters that performed this type of w ork as part o f their job activities w ould have had signifi cant airborne asbestos exposures when rem oving tightly adhered gaskets on flange surfaces, U nder normal lighting, airborne dust is invisible even though th e asb esto s levels m easured are above OSBA excursion limits. Therefore, an individual removing asbestos-containing gaskets w ill be unaware of any airborne exposure problem s under nor m al w orking conditions, High-intensity lighting (Tyndall Effect) was used by tbe investigators in these studies to observe expo sure mechanism s for workers performing norm al work activities. T he Tyndall Effect documented fiber release mechanisms and th e p ath w ay s o f exposure to the individuals rem oving the gas kets. Tyndall lighting is an alternative technique that industrial hygienists can use to check potential airborne dust emissions in the workplace. T he Tyndall lighting technique can visually dem onstrate to workers and employers if there is a need for air sam pling, additional ventilation, respiratory protection, and/or special w ork practices. T here are still significant numbers o f asbestos gaskets cur rently being used in the United States. O SH A classifies the TABLE V ffl T E M fabric and surface dust contam ination levels Studies Fabric-fibers/cm2 Surface dust-fibers/em2 Study 1 Study 2 Study 3 981 thousand 3.2 million 19.3 million 8.5 million 27.8 million 57.4 million All background control samples and field blanks analyzed were be low the analytical detection limit FIBER RELEASE DURING REMOVAL OF ASBESTOS 61 FIGURE 1 Scanning electron micrograph o f the surface of a new asbestos-containing gasket. Both the chrysotile fibers and polym er m atrix are visible. M agnification lOOOx. FIGURE 2 Scanning electron.m icrograph o f the surface of a used asbestos-containing gasket T he majority o f the materia] p re s e n ts only chiysotile asbestos. M agnification lOOOx. rem oval of asbestos-containing gaskets as Class H work o f short duration.^35! This specification by Q S H A only addresses a sin gle gasket removal p ro ject However, interviews with pipefit ters and machinists indicate that only removing one gasket at a time was not a typical occurrence. Under current OSH A reg ulations, the rem oval o f asbestos-containing gaskets requires the use of a glove bag and welting methods to contain the re le a s e o f asbestos fibers into th e w orkplace. U nfortunately, Che g lo v e bag and w etting m ethods are not alw ays practical in an actual workplace due to production and maintenance sched u le pressures and the difficulty in wetting a rubber based gasket. T he results of these studies indicate that employers need to de term ine if asbestos-containing gaskets are present in their equip m ent. The em ployer m ust im m ediately comply with O SHA's C lass II provisions by im plem enting a safe operating proce dure that includes employee training, assessmentimonitoring, containment, and good work practices. The following actions are recommended if asbestos-containing gaskets are removed w ithout a glove bag and wetting: (1) A negative pressure en closure should be used, (2) The enclosure should have a HEPA filtering/air blower system. (3) A HEPA vacuum cleaner and w etting agents should be used, and (4) The w orker should wear a respirator appropriate for the airborne asbestos concentrations generated by rhe activities. The data presented here demonstrate that the work surfaces io these studies as well as the clothing worn by the investigators were highly contaminated with asbestos fibers. An asbestoscontam inated w orkplace can lead to additions] asbestos expo sures. T he disturbance of the dust around the w ork area by other work activities and housekeeping activities will re-emrain as bestos fibers into the air.(35>The w earing, changing, and washing of the contam inated clothing can also lead to asbestos exposures for both a worker and family members. 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