4.1.2. Bulk samples
In order to determine the presence of silica and the relative per-
centage of different forms of silica (quartz, cristobalite, tridymite),
settled dust was collected as bulk samples since the bulk sample
should be representative of the airborne dust to which the workers
are being exposed NIOSH (1998a,b).
4.1.3. Field blanks
Certain numbers of blank samples are required by NIOSH 0600
and 7500 methods: 2–10 per set (NIOSH 0600, 1998; NIOSH 7500,
2003). One field blank was taken for every ten samples gathered
during the course of the project. The field blank cassettes were
stored in the same conditions as the cassettes used for air sam-
pling. The protocol used for acquiring field blanks consisted of:
(1) opening the cassette, (2) attaching the cassette to the cyclone
and sequentially to the sampling train, (3) allowing the cassette