- 5<=+

done under the same conditions of pressure temperature and density as will be
encountered. Where this is not possible it should be considered in the
calculations of the volume of air.. The rotameter should be used in the field
as a check if the diaphragm or piston pumps are not equipped with pulsation
dampeners. The pulsating flow resulting from these type of pumps causes the
rotameter to give results which are not accurate. Calibration can be
accomplished with any of the other standard calibrating instruments such as
spirometer, wet test meter, and dry gas meter. The rotameter was selected

because of its accuracy, availability and ease of operation.
(b) ANALYSIS OF ASBESTOS SAMPLES BY OPTICAL PHASE CONTRAST MICROSCOPY

Ve SCOPE

The equipment and procedures necessary in mounting, sizing and count-_
ing asbestos fibres obtained by standard sampling techniques are described.
The method applies to samples collected on membrane filters and only considers
those asbestos fibres greater than 5 pm in length with an aspect ratio of at

least 3 tol.

2. APPARATUS

(i) Filter Mounting Equipment

Filter samples should be mounted in a clean environment to avoid
contamination. The following items will facilitate the mounting of -
the sample.

- Microscope Slides: Glass slides of 2.5 x 7.5 cm. are used. Those
with a frosted end are preferable so that sample data can be easily
recorded.

= Cover Slips: Cover slips of a size sufficient to cover the filter
wedge are required. A #14 (17mm)/ cover slip is generally used as
most objectives are optically corrected for this thickness.

- Scalpel: A scalpel is required to clean. and easily section the
filter sample.

= Tweezers: A pair of tweezers is required to remove the filter
sample from its holder and in placing the sector to be analyzed
on the glass slide.

- Lens Tissue: A lens tissue (lint-free) is used to clean all
mounting equipment and slides prior to use. Ws