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health and safety laboratory - Digital Collections

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I<br />

PROCEDURE<br />

FOR GUMl/IED FILM<br />

I Sampling<br />

• The sampling medium is a rubber base cement spread on a 13" x 13"<br />

• cellulose acetate backing <strong>and</strong> covered with glassine paper for protection.<br />

• For sampling, the glassine is removed <strong>and</strong> the film attached to a cadmiumplated<br />

steel frame having a one foot square opening. The frame is held<br />

I three feet above the ground on a st<strong>and</strong>. Each paper is exposed for twentyfour<br />

hours, the sampling being started at 1230 Greenwich Civil Time at each<br />

JB station. At the end of the sampling period fresh films are put in place on<br />

• spare frames <strong>and</strong> exchanged with the exposed films. The exposed films are<br />

stripped off <strong>and</strong> folded with the gummed sides together into a size suitable<br />

M for mailing. Most sampling stations collect duplicate samples, <strong>and</strong> the two<br />

samples plus a field data card giving the location, date of sampling, <strong>and</strong><br />

Jl weather information are forwarded to the Health <strong>and</strong> Safety Laboratory.<br />

tit Sample Preparation<br />

An important point in processing is maintaining identification of the<br />

• sample from receipt to the reporting of the analytical results. For this<br />

purpose a six digit serial number is assigned to each sample. The first<br />

• three digits indicate the day of analysis on a counting house calendar basis,<br />

• while the last three digits indicate the number of the sample run during that<br />

day. When the sample envelope is opened, a prenumbered label is placed on<br />

• the data card <strong>and</strong> the gummed films are placed in steel cans for ashing.<br />

These ashing cans are used as crucibles <strong>and</strong> are discarded after a single use.<br />

I For convenience <strong>and</strong> speed of operation they are held in groups of ten in a<br />

m stainless steel rack <strong>and</strong> the rack number <strong>and</strong> position within the rack are<br />

the actual indication of sample number for each can,<br />

- 32 -<br />

i

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