The Brazilian Method for the Determination of Airborne Inorganic Fibres Concentration ( Including Asbestos Fibres )-Membrane Filter Method t

This paper reports a historical description of the "Brazilian Method For The Determination Of Airborne Inorganic Fibres Concentration (including asbestos fibres)Membrane Filter Method" since the creation of the Technical Group Organization for the study of the several existing methods in 1987, until the publication of the definitive method by "ABNTAssociar;ao Brasileira de Normas Tecnicas" (Brazilian Association for Technical Standards) in 1994. The Brazilian Method is very similar to the methods from AlA -Asbestos International Association, to NIOSHNational Institute for Occupational Safety and Health, and ISOInternational Standards Organization in collecting samples, preparation and analysis. The main differences are the counting criteria which do not consider the fibre aggregate particulate matter.


Introduction
The main reason of Brazil's interest in asbestos and its problems, is that this mineral is one of the national goods in its domestic economy.In 1994, Brazil arises as a great world producer, with 182.000 t./ year production.
This production, exclusively of chrysotile asbestos, is originated from only one mine located in Goias State, where asbestos is one of the greatest tax incomes in the State.About 60% to 70% of this production is used in the Brazilian market, the remainder being exported, mainly to Japan, Thailand, India and "Mercosul" -The South America Common Market.

Historical Note
The evaluation of the asbestos fiber concentration in the occupational environment has been introduced in Brazil during the 70's through a private initiative of some companies that were using asbestos as a raw material.
As there was not a Brazilian methodology for this purpose, the companies chose the "Reference Method For The Determination of Airborne Asbestos Fiber Concentrations At Workplaces By Light Microscopy * ABRA-Associa<;ao Brasileira do Amianto R. Beira Rio, 57 1 o andar Vila Olfmpia 04548-050 Sao Paulo-S.P. Brasil t Received 15 Feb. 1996 104 (Membrane Filter Method)'' RTM1 from the AlA-Asbestos International Association because most of the companies in Europe selected this method for control.
In the mid eighties', ''Fundacentro-Fundac,:ao Centro Nacional de Higiene e Medicina do Trabalho Jorge Duprat de Figueiredo'', (Fundacentro-Occupational Medicine and Hygiene National Centre Foundation) linked to the Ministry of Labour, responsible for Governmental Counselling relating to Occupational Hygiene Safety and Health, introduced the measurement of asbestos fiber concentration using the American Methodology of NIOSH-National Institute for Occupational Safety and Health.
In July 1987, by initiative of ABRA-Associac,:ao Brasileira do Amianto (Asbestos Brazilian Association) organization that, at this moment, is composed by 60 companies which use and process asbestos, with the purpose of promoting asbestos utilization in controlled and safety conditions, the CEA-Comite de Estudos do Amianto (Committee for Asbestos Studies) was created.The Committee objectives are to develop studies of general interest on the use of asbestos in safety conditions, as proposed by the Convention 162, of the ILO-International Labour Office, and to collect Brazilian and International information about statistical and technical data, with the main goal of keeping all parts well informed.
The Committee emphasized the importance of gathering professionals of various fields as: medical doctors, engineers, scientists, lawyers, technical politicians, and people interested in the subject, with partnerships between Government, Business and Workers Unions.
This Committee organized in 1987, as many work groups with the purpose of developing specific studies.The objective of one of these working groups was the elaboration of a Brazilian method for the determination of airborne asbestos fiber concentrations, because all the existing methods presented some differences one from each other, so the comparison between results was not possible to evaluate the most adequate to Brazilian conditions.
This group was mainly composed by technicians involved with governmental and industrial fields and the following fiber evaluation methods were the basis for discussion and experimentation: -RTM 1 by AlA (Asbestos International Association); -Method n. 7.400-B by NIOSH (National Institute for Occupational Safety and Health); U.S.A. -ISO method (International Standards Organization); -MDHS-39/2 by H.S.E.(Health and Safety Executive)-England.
After two years of meeting, discussion and experiments, the text of the Brazilian Method was developed by the Technical Working Group and approved by the Workers Labour Union for general use.
In the beginning of 1990 the text was sent to ABNT-Associac;:ao Brasileira de Normas Tecnicas (Brazilian Association for Technical Standards), organization responsible for the normalization in Brazil.The method was normalized, after one year and a half, with some alterations, into NBR 13.158-EvaluationOf Airborne Chemical Agents-Airborne Respirable Inorganic Fibers Collection And Phase Contrast Optical Microscopic Analysis-Membrane Filter Method, which became valid from June 30, 1994.

Characteristics of the Brazilian Method
The Brazilian Method in its essence is an association between the AlA-RTM 1, and Method n. 7.400-NIOSH.Basically it consists in the standardizing of the systematic sample collection and in establishing criteria for fiber analysis, measurement, and counting.The sample collection consists in the passage of the defined amount of air to be sampled through the membrane filter where the particulate airborne material will be separated.
The membrane filter is made from cellulose nitrate or from a mixture of cellulose esters, with 0.8 ~m to 1.2 ~m pore size, filter diameter of 25 mm with a printed grid, available in the general market.The filter holder should be open faced with an extension tube for filter protection made of electrically conductive material, like polypropylene saturated with carbon or metal, for the prevention of the electrostatic attraction of the fibers.
The sampling pump should be portable, with low flowrate and battery operated that allows the running for, at least, 8 hours continuously, with a constant flowrate of l.OL!min., free from pulsations.The pump flowrate should be calibrated using the prime pattern, (soap bubble method, or another one permissible).
For sample analysis, the filter should be mounted on a microscope stage and cleared with Acetone vapor and Triacetin (Giyceryl Triacetate).For fibers measurement and counting a phase contrast microscope should be used, with 400 to 500 times magnification.
The Brazilian Method specifies and details each step of the sampling collection processes and analysis, advising to each particularity with the purpose of preventing errors and allowing the results reproducibility.Such as the majority number of the methods which use the optical microscopy technique, the Brazilian Method presents a coefficient of variation around 20o/o in quality control conditions, if 100 fibers are counted.
The Method adopts for counting, the Walton-Beckett graticule, (Figure 1) reference G-22 (relation 3:1), diameter of 100 (m for 400 or 500 times magnification used during the microscopic analysis.
It is inserted in one of the oculars of the microscope.For sample analysis, the number of fibers counted are those which lay in the interior of the area of the Walton-Beckett graticule, named field.100 fibers or 100 fields should be counted, or at least 20 fields, even if 100 fibers have been already observed in the fields.
As the effective filtration area of the membrane filter being (A), the area of the counting field (a), the volume of the sampling air (V), the number of the counted fibers (n[) and the number of the counted fields (ng) are known, it is possible to calculate the fiber concentration (C) in the air sampled, by the following equation: The measuring units of the above variables should be chosen for the concentration to be expressed in fibers per mililiter (f/ml.).

Main differences between the Brazilian method and the AlA and NIOSH methods
The Brazilian Method was established for the inorganic fiber collection and evaluation, including asbestos, with a refractive index different from 1.43, which is the refractive index of the preparation of the membrane filter plus acetone vapor and triacetin.
The companies were already using the AlA-RTMl method, when Fundacentro, years later, began to use the NIOSH-7.400B method.
As there was not a defined method, each one adopted his own, among the several existing methods, but this criteria brought many difficulties in comparing results.Some companies did not give up the AlA-RTM1 Method, because its counting criteria favoured the companies samplings by bringing a lower result in the concentration of fibers in the occupational environment.
This method considers the diameter of the particle when it is attached to the fibre.If it is bigger than 3 ftiD the fibre is not counted, while the NIOSH-7.400B method omits the attached particle, independently of its diameter size and counts it if the fibre follows the definition criteria.

Counting criteria
The reason for counting the fibers aggregated with particles is due to the Brazilian plants conditions, i.e., mainly in the asbestos cement and brakelining sectors, where an expressive amount of particulate 106 materials among the fibers, is found.This situation raises difficulties to the fibers counting, because no one can not affirm if there is a particulate adherence to the fibers or superposition of it to the fibers.
Concerning to more strict results, the counting criteria relating to the Brazilian Method-ABNT is supposed to count individually the fibers in a bundle, if they can be distinguished separetely.If it is not possible identifying them in an individual way, the fibers associated to other particles or to themselves, should be counted as one fiber, following the fiber definition.
A fiber is counted as one, when it presents both defined ends entirely in the interior of the graticule and its diameter should be measured in the non-divided part; the fibers which are gathered to other particles are counted as fibers, independently of the aggregated particle diameter also following the fiber definition that recommends that the respirable fiber diameter be lesser than 3 ftill, length longer than 5 ftiD, and the relation between length and diameter higher than 3:1.

Quality control
It is extremely important that reliable and reproducible results should be obtained.Related to this objective there is a participation in international programs of interlaboratorial quality control sponsored by LHCF-''Laboratoire d'Hygiene et des Controles de Fibres Minerales" (France) and IOM-"Institute of Occupational Medicine" (Edinburgh).The mentioned laboratories send a set of slides, already prepared, so the technicians count the fibers using an optical microscope.The results are sent to them in order to obtain the due qualification.The LHCF compares the result from the counter, following the average of the results from all the counters participating to the program and classify it according to the standard deviation and variation coefficient.The IOM compares the results from the counter using visual reference counts and Magiscan reference counts, classifying them according to the percentage zone limits.

Results
Due to the sensibility inherent to the method, all calculated value of less than 0.1 fiber/ml and all higher value, is rounded off to the first decimal place.
The results showed in years, sampled from asbestos cement and brakelining industries, also from other asbestos using industries.The analysed points were sampled from the operators in order to check the exposure level to which they are submitted.
The measurements realized by ABRA in industries aim to inspect all the industry sectors, and the points are chosen by ABRA technicians and workers at workplaces where there is the possibility of dust formation.
The importance of these evaluations is also to indicate if the collective control measures are efficient enough, and to check the correlation between the exposure level and epidemiological studies ( doseresponse).
The evaluations are carried out in intervals not higher than six months considering the valid Brazilian health rules for asbestos using factories.

Figure 2 Fig. 2
Fig.2Level of airborne chrysotile asbestos fiber concentration evolution in the asbestos cement industries