vastthought.blogg.se - Personal breathing zone sample

Smaller air volumes may be necessary when there is excessive non-asbestos dust in the air. If more than about 25 to 30% of the field area is obscured with dust, the result may be biased low. High levels of non-fibrous dust particles may obscure fibers on the filter and lower the count or make counting impossible. Note: Do not overload the filter with dust. Suggested maximum air sample volumes for specific environments are:Īsbestos removal operations (visible dust)Īsbestos removal operations (little dust) The most significant problem when sampling for asbestos is overloading the filter with non-asbestos dust.For Excursion Limit (30 min sampling time) evaluations, a minimum air volume of 48 L is recommended. A suggested minimum air volume when sampling to determine TWA compliance is 25 L.Secure the cassette on the collar or lapel of the employee using spring clips or other similar devices. The distance from the nose/mouth of the employee to the cassette should be about 10 cm. Assure that each sample cassette is held open side down in the employee’s breathing zone during sampling. Remove the end cap of each cassette and take each air sample open face. Connect each pump to the base of each sampling cassette with flexible tubing.If possible, calibrate at the sampling site. bubble burette) to calibrate each pump or a secondary standard such as a rotameter. Calibrate each sampling pump before and after sampling with a calibration cassette in-line (Note: This calibration cassette should be from the same lot of cassettes used for sampling).Always choose a flow rate that will not produce overloaded filters.

The sampling flow rate must be between 0.5 and 5.0 L/min for personal sampling and is commonly set between 1 and 2 L/min.

Select an appropriate flow rate for the situation being monitored.

Connect each pump to a calibration cassette with an appropriate length of 6-mm bore plastic tubing.

To reduce contamination and to hold the cassette tightly together, seal the point where the base and cowl of each cassette meet, with a gel band or tape.

Charge the pumps completely before beginning.

(Please note the use of a rotameter is an industry standard and not part of the NIOSH 7400 method.)

Pump calibration: Stopwatch and bubble tube/burette, electronic meter, or rotameter.

Wire, multi-stranded, 22-gauge 1”, hose clamp to attach wire to cassette.

(0.80 μm pore size filters are recommended for PCM analysis and 0.45 μm pore size filters are recommended for TEM analysis.)

Sampler: field monitor, 25-mm, three-piece cassette with 50-mm electrically conductive extension cowl and cellulose ester filter, 0.45 to 1.2 μm pore size and back up pad.

So for some exposures, substantially more fibers may be present than are actually counted.

The smallest visible fibers detected by PCM usually are about 0.2 μm in diameter while the finest asbestos fibers may be as small as 0.02 μm in diameter.

Other fibers that are not asbestos may be included in the count.

The analytical technique does not positively identify asbestos fibers.

Phase contrast is a fiber counting technique that excludes non-fibrous particles from the analysis.

The analytical technique is specific for fibers.

To assess whether the levels present suggest an elevated fiber concentration.

To capture and quantify the amount of airborne asbestos and non-asbestos fibers present in the air.

Note: While this guide recommends common practices, other requirements might vary by state and/or agency.

Asbestos PCM Air Sampling Air Sampling for PCM Analysis