Technique of Analysis of Air Samples for Asbestos

There are particular procedures in the analysis of air samples for asbestos and particularizes quality control processes that should be put into practice by science laboratories carrying out the investigation with the aid of microscopy using a microscope such as asbestos microscope. The sampling and investigative techniques signify the elements of the accessible monitoring processes that are significant in order to attain sufficient employee exposure monitoring while permitting employers to utilize techniques that are already recognized within their organizations. Altogether, employers who are needed to conduct air monitoring are asked to use analytical science laboratories that utilize this technique, or an equivalent process, for gathering and investigating samples.

In the sampling and investigative process, the sampling medium for air samples will be combined cellulose ester filter membranes. These will be assigned by the company as appropriate for asbestos counting. The chosen gathering device will be the twenty-five millimeters diameter cassette with an open-faced fifty millimeters extension cowl. The thirty-seven millimeters cassette may be utilized if needed but only if written explanation for the necessity to utilize the thirty-seven millimeter filter cassette complements the sample outcomes in the employee’s exposure monitoring document. Never recycle or refill cassettes for asbestos sample gathering. An air flow speed between half a liter per minute and two-and-a-half liters per minute will be chosen for the twenty-five millimeters cassette. If the thirty-seven millimeters cassette is utilized, an air flow rate between one liter per minute and two-and-a-half liters per minute will be chosen. Where feasible, an adequate air volume for every air sample will be gathered to produce between one hundred and one thousand three hundred for every square millimeter on the membrane filter. If a filter darkens in outward show or if loose dust is noticed on the filter, a second sample will be taken. Transport the samples in a firm container with adequate packing material to avoid displacing the gathered fibers. Stuffing material that has a high electrostatic charge on its face like expanded polystyrene cannot be utilized because such material can initiate loss of fibers to the edges of the cassette. Regulate every personal sampling pump prior to and subsequent to application with a representative filter cassette fixed between the pump and the calibration tools. Personal samples will be obtained in the respiration or breathing zone of the employee fastened to or close to the collar or lapel near the face of the worker. Fiber counts will be done by means of microscopy using a microscope like positive phase contrast or an asbestos microscope. The asbestos microscope or the phase contrast microscope will also be fitted with a blue or a green filter. The asbestos microscope or the phase contrast microscope will be fitted with a Walton-Beckett eyepiece graticule regulated for a field diameter of one hundred micrometers (+/- 2 micrometers). The phase-shift determination limit of the microscope will be around three degrees that is measured utilizing the HSE phase shift microscope test slide. Put the microscope test slide on the stage of either asbestos microscope or phase contrast microscope and center it under the objective. Bring about the blocks of grooved lines into center.

The microscope slide has seven sets of grooved lines in downward order of visibility from sets one to seven, seven being the least noticeable. The necessities for asbestos counting are that the optics of the phase contrast microscope or asbestos microscope should work out the grooved lines in set three absolutely although they may look rather faint, and that the grooved lines in sets six and seven should be unnoticed. Sets four and five should be at least moderately noticeable but may differ slightly in visibility between the microscopes. A phase contrast microscope or asbestos microscope that falls short in meeting the said requirements has either very low or very high a resolution to be utilized for asbestos. In case the image worsens, clean and regulate the optics of the phase contrast microscope or optics of the asbestos microscope. If the problem subsists, ask the microscope company. Every set of samples obtained will have ten percent field blanks or a minimum of two field blanks. These blanks should come from the identical lot as the filters utilized for sample gathering. The field blank outcomes will be averaged and subtracted from the analytical outcomes prior to reporting. A set has any sample or group of samples where an assessment for this standard should be done. Any samples denoted by a field blank containing a fiber count in excess of the determination limit of the technique being utilized will be rejected. The samples must be mounted by the acetone or triacetin technique or a technique with an equivalent index of refraction and analogous clarity. Count only the fibers that are equal to or longer than five micrometers as observed under the microscope such as asbestos microscope. Gauge the length of curved fibers along the curve using the asbestos microscope. Count every particle as asbestos that contain a length-to-width ratio of 3:1 or higher as viewed under the asbestos microscope. Fibers lying completely inside the boundary of the Walton-Beckett graticule field will receive a count of one. Fibers that cross the boundary once, containing one end inside the circle, will receive the count of one half. Never count any fiber that intersects the graticule boundary more than once as viewed under the asbestos microscope. Deny and do not add up any other fibers although they may be apparent outside the graticule section. Count the bundles of fibers as one fiber except when individual fibers can be recognized by observing both ends of an individual fiber using the asbestos microscope. Count adequate graticule fields to produce one hundred fibers. Count at least twenty fields, and then stop counting at one hundred fields despite of fiber count. Blind recounts will be performed at the rate of ten percent.