Since the circle diameters vary logarithmically, every

other circle doubles in diameter. Thus:

1 S6aum .

D, =52ax Dd =

D,= 2x Dd, = 2.64 pm,
Ds =2x D, = 3.72 pm
De =2x D, = 5.28 ym

COUNTING AND SIZING

For each field investigated, count only those fibres 5 pm in

length with an aspect ratio of at least 3:1.
Count any fibre 5 ym if it is entirely within the field area.

If some portion of the fibre extends out of the field area then
only count that fibre if it crosses one or both of adjacent
pre-selected sides. It is convenient to use the left and bottom

sides of the field area as these reference sides.

Count as many fields as required to yield at least 100 fibres.
In general the minimum number of fields should be 20 and the

maximum 100.

The counting fields are selected without looking into the eye-

piece.

The fields are selected in a straight line running from the tip
of the wedge (centre of filter) to the centre of the arc side
(circumference of the filter). If further counts are required to
achieve the necessary 100 fields, these are selected along
straight lines parallel to and slightly above or below the

original counting line.

Do not count a field containing more than 20 fibres unless there

is very little fibre overlap and few background particulates.

When an agglomerate of particulates covers 1/6 or more of the

field area, reject the field and count another.