Filtration and Sampling of Aerosols by Fibrous Filters - Aerosols: Measurement, Dosimetry, and Health Effects - page 460

17.10 FIBROUS FILTERING MATERIALS OF FP TYPE
Fibrous FP iltering materials are statistically uniform and homogeneous [115] layers of charged
ultraine polymer ibers. The ibers are produced by drawing of polymer solution under action of
an electrostatic ield (electrospinning technology) [19]. At present more than 40 FP iltering materi-
als made from different polymers are developed in the Karpov Institute of Physical Chemistry and
Russian industry produces several millions square meters of iltering materials annually. Some inter-
national companies, such as Hollingsworth & Vose Company, Donaldson Company, Inc., and some
others, are also active currently in the production of iltering materials by electrospinning technology.
FP iltering materials are produced as rolls or cloth sized 0.6 × 1.6 m. They are used for production
of respirators, analytical ilters, and aerosol ilters of HEPA and ULPA classes. FP iltering materials
for analytical iltration are used in high capacity aspirators designed for air intake of hundreds and
thousands cubic meters per hour. Airplane devices for sampling of atmospheric aerosols (iltering
pods) may have capacity up to 20,000 m 3 /h [116]. They can accommodate up to 6 m 2 of iltering
material. FP iltering materials are easily pressed after sampling into compact premolds (tabs), which
is especially convenient at measuring of radioactive aerosols containing gamma-radiation sources.
Portable or stationary sampling devices are used at industrial premises. They contain analytical
AFA aerosol ilters having surface from 3 to 20 cm 2 . Capacity of such devices is relatively small
(dozens to hundreds l/min) but it is quite suficient for dosimetric purposes.
AFA analytical ilters are also produced from FP iltering materials. They constitute disks of a
iltering material, whose edges have paper spacer with a ixture for installation of the ilter into the
ilter holder. A list of basic AFA ilters produced by Russian industry is given in Table 17.3 [117].
Filtering belts (ribbons) are used in devices for continuous monitoring of radioactive aerosols.
Analytical NEL-3 iltering belt has been developed for using in devices for measurement of
dust weight concentration by absorption of α- or β-radiation from a standard radioactive source in
captured sediment. The belt constitutes a uniform layer made of ultrathin ibers' mixture having a
diameter of 5-7 and 0.5 μm and thickness of 1.5 ± 0.2 mg/cm 2 .
NEL-4 iltering belt is designed for use in devices for measuring aerosol concentration (volumet-
ric activity) by radiometric, optical, and chemical activation and other methods. The belt may also
be used for aerosol sampling at enhanced mass concentration up to building of dust sediments on
the iltering layer of 2.5 mg/cm 2 . The belt is used at ambient air pressure that is lower than atmo-
spheric as well as for sampling at high rates of iltration. NEL-4 iltering belt constitutes a uniform
layer made of ultrathin ibers' mixture having diameter of 7 and 1 μm. Thickness of the layer is
4.0 ± 0.5 mg/cm 2 .

TABLE 17.3
Russian Filters for Aerosol Analysis

Type of AFA
Filter

Filter Denomination
by Method of Analysis Function

AFA-HP
AFA-HA

Determination of concentration of chemical and
radiochemical aerosol composition

Chemical

AFA-RMP
AFA-RMA

Determination of volumetric activity of aerosols Radiometric

AFA-RSP Determination of volumetric activity and isotope

composition of aerosols

Radiospectrometric

AFA-RGP Determination of aerosol particle sizes and activity Radiographic

AFA-VP Determination of aerosol weight concentration Weight

AFA-DP Determination of aerosol particle sizes under microscope Dispersive

AFA-BA Determination of aerosol concentration Bacterial