Document aJNmpbjaRo2aM4wj2y2Zo7pjY

FILE NAME Packings and Gaskets PAG DATE 1996 DOC PAG010 DOCUMENT DESCRIPTION Journal Article - Exposure to Asbestos Fibres During Gasket Removal Pergamon OccupationalHygiene Published Elsevier pp Ann occup Hyg Vol 40 No. 5 583 5881996 Copyright 1996 British Hygiene Society by Elsevier Science Ltd. Printed in Britain Great 0003-4878 96 15.00 +0.00 0003-4878 EXPOSURE TO ASBESTOS FIBRES DURING GASKET REMOVAL S. K. Spence and P. S.J. Rocchi ARCO Chemical Ltd Rotterdam The Netherlands and Shell Netherlands Refinery Hoogvliet The Netherlands Received in final form 24 August 1995 Abstract the chemical industry asbestos gaskets have been used extensively to prevent leakage between solid surfaces The purpose of this study was to assess the potential personal exposure to asbestos fibres during gasket renoval and thus to determine what is reasonably required in terms of protective regime and work method Two groups were studied group A who only removed gaskets if they could be removed easily and without breaking and group B who removed gaskets which were left by the first group For both groups the gasket was first made wet before removal The The samples were analysed using contrast microscopy and transmission electron microscopy average exposure to fibres for group A averaged over the work period was 0.04 0.24f2ibres mlfl as determined by contrast microscopy On further analysis with transmission electron microscopy it was found that only four of the 11 samples contained asbestos in very low concentrations and that most of the fibres which were identified using contrast microscopy probably originated from the glass fibre lagging around the pipes For group B the average fibre determined concentration averaged over the work period as by contrast microscopy ranged between below the detection limit and 0.02 fibres ml The subsequent transmission electron fibres microscopy analysis shows the exposure to asbestos fibres ranged between below the limit of that detection to 0.004 fibres ml This study shows that the exposure to asbestos during gasket fibres removal activities was well within the h average exposure limit of 0.3 fibres mi Copyright ' 1996 British Occupational Hygiene Society INTRODUCTION In the chemical industry asbestos gaskets have been used extensively to prevent leakage between solid surfaces With time the effectiveness of the seal may become compromised and therefore they are replaced periodically Normally they are replaced on an ad hoc basis However during a major maintenance overhaul of a > chemical facility called a turnaround hundreds or thousands of gaskets may have to be replaced over a period of a few days by maintenance teams Typically these activities are carried out by maintenance personnel from contracting companies who go from turnaround to turnaround performing similar jobs Therefore if there is a potential hazard through exposure to asbestos fibres then it is these individuals who are at most risk Nowadays the use of asbestos is limited by restrictions which are legislated in both European and North American countries These restrictions are naturally due to the potential of asbestos to cause cancer Eventually it is expected that all existing gaskets will be replaced by asbestos substitutes However at present many chemical plants still use asbestos gaskets in their facilities and it will Current address 32 Duthie Terrace Aberdeen AB1 6LQ U.K. 583 584 S. K. Spence and P. S. J. Rocchi probably be years before all of them have been substituted with asbestos alternatives Additionally in developing countries asbestos is still permitted and continues to be used for many applications including gaskets Therefore it is important to determine whether there is a health risk associated with the removal of gaskets The three major types of gaskets used in the chemical industry are sheet or plate gaskets spiral wound gaskets and metal jacketed gaskets For the metal jacketed type the gaskets are completely encapsulated by metal as the name suggests These were not considered in this study Spiral wound gaskets consist of a crysotile asbestos filler material compressed between stainless steel spiral windings They typically fall out as soon as the pressure on the seating surfaces has been released Plate gaskets are compressed sheets of crysotile asbestos bound together with nitryl or neoprene When plate gaskets have been sitting in an installation for a long period under pressure and exposed to chemical agents they may become damaged and fixed In order to remove them and leave a clean surface on which to put a new gasket scraping may be required This increases the chance of asbestos fibres becoming airborne and maintenance workers exposed There are not many studies in the literature which document the exposure to airborne asbestos during gasket removal McKinnery and Moore 1992 looked at both removal of gaskets and packing material For gaskets the average monitoring period during removal for five samples was 31 min On analysis using contrast microscopy PCM the fibre concentration ranged between 0.049 and 0.44 fibres ml Further analysis was done using transmission electron microscopy TEM The concentrations found using TEM were higher 0.86-18.55 structures ml however for this study the analysis method did not allow a direct comparison between PCM and TEM Another study done by Millette and Mount 1993 looked at removal of dry packing material for three samples monitored over periods ranging between 25 and 33 min They found fibre concentrations between 0.2 and 1.0 fibres ml using PCM analysis On analysing using TEM and converting to the PCM equivalent fibre concentration was higher ranging from 1.5 to 2.6 fibres ml These two studies by McKinnery and Moore 1992 and Millette and Mount 1993 both used a simulated work environment Cheng and McDermott 1991 looked at the difference between wet and dry removal of asbestos gaskets in a real work situation The analysis method used was limited to PCM They found that the average fibre concentration of four samples using dry removal was 0.11-0.33 fibres ml . The sampling duration ranged between 19 and 55 min For wet removal fibre concentrations for two samples were below 0.06 fibres ml The sampling duration for the first and second sample was 15 and 30 min respectively . The purpose of this study was to assess the potential exposure to asbestos fibres during a real work situation and to determine what is reasonably required in terms of protective regime and work method This second point was important in the light of legislation in The Netherlands covering asbestos activities Ministry of Social and Work Affairs 1993 which was valid at the time of the study In The Netherlands at the time of this study all asbestos activities were classified under one general rule which describes the protective measures to be taken during these activities Exposure to asbestos during gasket removal 585 1 Workers must wear personal protective equipment HEPA filter face mask respiratory protection hooded coveralls gloves and boots 2 The area must be cordoned off during removal activies 3 There must be a personal decontamination procedure in place 4 Individuals employed must be trained in the hazards of asbestos 5 Area monitoring must take place at the end of the job in order to declare the area asbestos 6 Asbestos removal activities must be reported beforehand to the authorities For gasket and packing removal step 5 is not required and step 6 can be done once a year to a cover gasket removal for the whole year This regime when applied to gasket removal is logistically challenging conservative and expensive given the tight time schedule of a turnaround and the number of concurrent activities which are carried out in the same location A compromise position was adopted whereby two work methods were applied for the removal of asbestos gaskets METHOD Group A Group A was the first pass group In the course of the maintenance activity when a gasket was to be removed the individual wore a P3 disposable half mask wet the gasket with a wetting agent and then an attempt was made to remove it with little effort and with only a putty knife If the gasket came out easily it was placed in a plastic bag for special disposal If the gasket proved difficult to remove or broke in the process it was left for group B. Employees from group A were working in sections of the plant where it was thought that asbestos gaskets would be encountered However it should be noted that there was no way of knowing for sure whether or not asbestos or substitutes would be encountered during the work activities All the gaskets which were removed were saved for bulk analysis Group B The gaskets which were left out during the first phase were removed by a team of trained individuals during the evening when there were limited personnel on site For this group the area was isolated and a full personnel protective regime of P3 power pack respiratory protection Protection Fact = o 20r0 hooded overalls boots and gloves was used Full decontamination procedures were followed at the end of the shift Again the gaskets were saved for bulk analysis Personal exposure monitoring was performed for both groups according to NVN 2939 1987 After sampling the filters were divided into two The first half was analysed using contrast microscopy PCM according to NVN 2939 1987 The second half of the filter was analysed using transmission electron microscopy TEM according to NIOSH 7402 1989 TEM distinguishes between asbestos and asbestos fibres whereas PCM does not It was felt that the additional analysis using TEM was necessary because other airborne fibres would likely be present since piping insulation mainly fibre glass was also removed in the same operation as gasket removal 586 S. K. Spence and P. S. Rocchi Owing to the expense associated with the TEM analysis it was decided beforehand that those samples which had a concentration of less than 0.015 fibres ml as determined by PCM would not be analysed by TEM This figure was selected since this represents the total exemption value according to Dutch legislation This means that when an area measurement is found to have a concentration of less than 0.015 fibres ml the area is considered free of asbestos Ministry of Social and Work Affairs 1993 RESULTS AND DISCUSSION Table 1 shows the results for group A. Group A removed between two and 12 gaskets per shift All gaskets were spiral wound The average fibre concentration for work method A was 0.042-0.242 fibres ml When converted to exposure averaged over 8 h it varied between 0.036 and 0.215 fibres ml On further analysis with TEM only four of the 11 samples contained asbestos in very low concentrations This is not surprising since on bulk analysis of the gaskets only five of the gaskets removed by group A contained asbestos This is unfortunately the possible outcome when a real life situation is chosen rather than a simulated environment These results are interesting however because of the relatively high concentration of fibres found by contrast microscopy These fibres probably came from the piping insulation which was removed prior to removal of gaskets Had the TEM analysis not been carried out there would have been erroneous over estimation of the airborne asbestos fibre concentration Table 2 shows the results for the second exposure group All the gaskets removed by group B were asbestos plate gaskets The work was intensive and represented a worse scenario since all the insulation was removed and the flange or equipment piece was already open This meant that full shift was spent only removing difficult to remove gaskets Each worker removed between three and 13 gaskets The average fibre concentration as determined by PCM ranged between below the detection limit and 0.02 fibres mi When this is converted to an h limit then the value ranges from below the detection limit to 0.005 fibres ml The TEM analysis that the exposure to asbestos fibres even in this worst scenario still remains well below both the limit value and the action limit even when looking at the statistics in terms of real time rather than averaging over 8 h The only value obtained above the detection limit was 0.0037 asbestos fibres ml CONCLUSIONS The results of this study show that personal exposures to asbestos are kept well below the current limit values in The Netherlands Using a suitable wetting agent provides adequate protection of the employee while limiting the cost and delay posed by unnecessary control measures Secondly contrast microscopy which has traditionally been used for this type of exposure monitoring situation may not be applicable where there are mixed fibres present This method overestimated the asbestos fibre concentration in this study It is interesting to note the legislative developments regarding asbestos in The Netherlands following the outcome of this study The Labour Inspectorate has Table 1. Exposure to airborne fibres for group A Total fibre Asbestos fibre Other Exposure concentration concentration inorganic fibres Sample Number of Time using PCM using TEM using TEM No. gaskets min 2 ml,, fml ml Comments to asbetos 1 2 432 0.068 Not detectable 0.043 One asbestos one asbestos both spiral wound 2 4 427 0.242 0.0012 0.0567 Two asbestos slightly damaged asbestos all spiral wound 3 9 400 0.098 Not detectable 0.0203 asbestos spiral wound 4 2 421 0.042 Not detectable 0.0074 asbestos spiral wound during 5 4 410 0.042 Not detectable 0.0258 asbestos spiral wound 6 G 400 0.093 Not detectable 0.025 asbestos spiral wound 7 2 430 0.051 8 S 416 0.056 9 5 425 0.052 0.0014 0.0009 0.0007 gasket 0.0157 0.0169 0.0151 asbestos spiral wound Two asbestos three asbestos all spiral wound asbestos spiral wound removal 10 147 435 0.051 Not detectable 0.032 One asbestos three asbestos all spiral wound 11 147 400 141 Not detectable 0.0289 asbestos spiral wound 587 588 S. K. Spence and P. S. J. Rocchi Table 2. Exposure to airborne fibres for group B Sample No. Number of gaskets Time min Total fibre concentration using PCM f ml Asbestos fibre concentration using TEM f ml) Other inorganic fibres using TEM f ml Comments 12345 23manmo 141 0.018 Not detectable 0.0144 All asbestos plate type 12345 23manmo 141 0.02 0.0037 0.0237 All asbestos plate type 12345 23manmo 71 Not detectable B Bee Te All asbestos plate type 4 23manmo 71 0.025 Not detectable 0.0413 All asbestos plate type S 13 156 0.005 . meee All asbestos plate type 6 9 156 Not detectable All asbestos plate type 7 23manmo 69 0.014 : g 23manmo 69 Not detectable All asbestos plate type All asbestos plate type g 23manmo 147 Not detectable All asbestos plate type 10 6 141 0.005 All asbestos plate type Black area indicates that the sample was not analysed by TEM recently published new draft guidelines which apply to removing asbestos gaskets These allow under certain conditions for Work Method A to be used for gasket removal activities Ministry of Social and Work Affairs 1994 For the employee adequate protection and ease of compliance is assured while for the employer the cost and complicated logistics associated with Work Method B are avoided This study shows another example of how it is possible for industry and legislative bodies to pull together on health and safety issues to study situations for mutual benefit REFERENCES Cheng R. T. and McDermott H. J. 1991 Exposure to asbestos from asbestos gaskets Appl Occup Environ Hyg 6 588-591 McKinnery W. N. and Moore R. W. 1992 Evaluation of airborne asbestos fiber levels during removal and installation of valve gaskets and packing Am ind Hyg Ass J. 53 531-532 Millette J. R. and Mount M. D. 1993 A study determining asbestos fiber release during the removal of valve packing Appl Occup Environ Hyg 8 790-793 Ministry of Social and Work Affairs 1993 blad Asbestos draft 6. General Director of Labour The Netherlands . Ministry of Social and Work Affairs 1994 blad Asbestos draft 7. General Director of Labour The Netherlands . ' NIOSH 1989 Method asbestos fibres In Manual of Analytical Methods 3rd Edn National Institute of Occupational Safety and Health Cincinnati Ohio U.S.A. NVN 2939 1987 Air quality determination of the concentration of asbestos fibres by light microscopy after active air membrane sampling Netherlands Standards Institute Delft The Netherlands