INDUSTRIAL HYGIENE SAMPLING STRATEGIES
AIR FLOW MEASUREMENT

 
OSH 626, LAB I

AIR FLOW MEASUREMENT


Purpose
This experiment allows the student to have a good understanding of the
equipment used in air sampling.  Students will use 6 types of meters 
and gauges for the measurement of air flow.  Air flow and volume
measurements are essential for determining the concentration of airborne
contaminants.


Part I
1) Calibration of a rotameter with a wet-test meter.
   The calibration train instruments must be set as shown below.

   WET-TEST METER-->ROTAMETER-->VALVE-->PUMP

 - Maintain rotameter readings @ 10, 30, 50, 70, 90, 110, 130, & 140
 - At each rotameter reading measure the time for 1 revolution on
   the wet-test meter.
 - Repeat each calibration point three times.
 - Calculate Q (l/min.) for each rotameter reading and plot results.
 - Keep and save the results and plot for later use.


2) Calibration of air flow through an impinger.
   The calibration train instruments must be set as shown below.

   WET-TEST METER-->IMPINGER-->MAGNAHELIC GAUGE-->
   -->VALVE-->PUMP

 - At impinger pressure drops of 8, 10, 12, 14, and 16" H2O,
   measure the time for 1 revolution on the wet-test meter.
 - Repeat each calibration point three times.
 - Calculate Q (l/min.) for each pressure drop and plot results.
 - Keep and save the results and plot for later use.


3) Calibrating a magnahelic gauge with a soap-bubble meter.
   The calibration train instruments must be set as shown below.

   SOAP-BUBBLE METER-->FILTER HOLDER-->MAGNAHELIC GAUGE-->
   -->(VIRTUAL) ORIFICE METER-->VALVE-->PUMP

 - At pressure drops of 5, 10, 15, and 20" H2O, measure the time
   that it takes the soap bubble to rise from 500 ml to 1000 ml.
 - Repeat each calibration point three times.
 - Calculate Q (l/min.) for each pressure drop and plot results.
 - Keep and save the results and plot for later use.


Note: Plot all results on arithmetic and logarithmic graph paper
      with the flow as the ordinate.


Part II
1) What is the probable error due to time measurement in these
   calibrations?

2) Over what range does the orifice follow the relationship of
   volumetric flow being proportional to pressure drop?

3) At what pressure ratio does the flow through the orifice become
   critical?


Part III
After the orifice meter was calibrated the soap-bubble meter was removed
and a 0.3 mm filter weighing 0.00002 mg was placed in the filter holder.
At a pressure drop of 18" H2O you sampled for two hours and immediately
after you were done with sampling you weighed the filter; your balance
indicated that the weight of the filter was 2.00345 mg.
Determine the concentration of the collected material in air in mg/m3,
and in ppm given that the molecular weight of this material is 35 g/mole
and that sampling took place at 20 °C and 29.92" Hg.