OSH 626, Industrial Hygiene Sampling Strategies

 1. 10 sampling tubes indicated H2S concentrations in mg/m3    
    as such:
              [10, 8, 7, 10, 6, 5, 10, 12, 10, 8]
    Calculate the following:
     - median
     - mean in mg/m3 and ppm
     - absolute deviation
     - standard deviation
     - coefficient of variation %
     - geometric mean
    Samples were taken at a pressure of 762 mm Hg and at a
    temperature of 73.4 F; MW: S = 32.1, H = 1 gm/mole.
 2. Assuming that the length of fibers is a function of the
    diameter, calculate the slope and the Y-intercept for the
    following observations:
           Diam. (mm)        Length (mm)
              0.5                2.0
              1.0                4.5
              2.5                7.0
              3.0                9.0
              5.0               11.5
    Also calculate the predicted lengths for the following
    diameters: 4, 6 and 8 mm.
 3. For the following particle size distribution calculate the
    geometric mean and the geometric standard deviation.
       particle size (mm)       freq.
            < 2.00                11
           2.01-4.00              84
           4.01-8.00             285
           8.01-16.0             370
          16.01-32.0             203
          32.01-64.0              43
            > 64.0                 4
    Use PROBABILITY-LOG graph paper to plot data.
 4. 29 samples of CO2 indicated a concentration of 60 ppm at an
    elevation of 5888 ft. where the pressure was 25.82 inches of
    mercury and the temperature was 16 F.  Calculate this
    concentration in mg/m3 and mg/l.

 1. Calculate the aerodynamic equivalent diameter of a 10 mm
    particle having a density of 2.65 gm/cm3.
 2. Determine the velocity of a 10 mm diameter particle settling
 3. A unit density particle 10 mm in diameter is settling in an
 unknown gas (density = 0.001 gm/cc) at a velocity of 0.545
 cm/second. Calculate,
    a) the viscosity of this gas.
    b) Reynolds #.
 4. A sample of H2SO4 was found to contain oil droplets.
    You are asked to centrifuge this sample to remove the oil
    droplets.  How long should you centrifuge?
     - density of oil = 0.8 gm/cm3
     - density of H2SO4 = 1.2 gm/cm3
     - viscosity of H2SO4 = 0.2 poise
     - diameter of oil droplets = 1.25 mm
     - length of centrifuge tube = 10 cm
     - radius (R) of sample holder in centrifuge = 20 cm
     - rpm (n) of centrifuge = 20200
               Vtan = [n][(2)(3.1416)/60][R]
 5. Calculate the settling velocity in air of a 0.5 mm dust particle
    having a density of 2.65 gm/cm3.
 6. Determine the stopping distance of a particle 10 mm in diameter
    settling in air at a velocity of 10 cm/sec.  STATE ALL YOUR
 7. Calculate the (MMD) of a particle distribution that has a CMD
    of 9.6 mm and a geometric standard deviation of 1.85 mm.

 1. A rigid type chamber has a volume of 1.5 m3 with air moving
    through it at a rate of 0.15 cfm. 
    Determine the sampling time needed to reduce the initial
    concentration of a certain gas in the chamber by 15%.
 2. Determine the injection rate in ml/min. for a contaminant with
    a molecular weight of 96.0 gm/mole and a density of 1.56 gm/cc
    used to generate a minimum concentration of 120 ppm in air.
    The flow rate of air moving in the mixing tube is 12 l/minute.
 3. Prove that for every 10.33 meters under water the pressure
    increases by 76 cm Hg.

   A survey was performed to determine the physical properties
   of a dust cloud in the Rocky Mountains 10,000 ft. high.
   At time of sampling the barometric pressure was 20.58" Hg and
   the temp. was 75 F.  Samples were collected on a membrane filter
   using a pump and a rotameter.  The reading of the rotameter
   indicated a flow rate of 10 l/min.  The weight of the dust after
   100 minutes of sampling was 5.0 mg.  The rotameter was calibrated
   in Murray at a pressure of 30.0" Hg and a temperature of 75 F.
   The density of the dust is 2.65 g/cm3.
   Evaluating this dust cloud for size distribution by a cascade
   impactor showed that 10% of these particles were < 2 mm and
   10% > 5.9 mm.
   At the same time an impinger with 10 ml. of water was used to
   collect particles for counting purposes.  Counting was done with
   a light microscope 10X eye piece, and 10X objective.  
   (NA = 0.147 & wavelength of light for illumination = 0.7 mm).
   The depth of the counting cell is 1 mm. and the counting medium
   is water with a density of 1.00 gm/cm3 and a viscosity of
   0.001 poise.
   a. The concentration of total dust.
   b. The diameter of the smallest particle visible by the microscope.
   c. The fraction of particles that will be visible as percent
      of the total number of particles in the dust cloud assuming
      that the impactor collected all sizes with 100% efficiency.
   d. The waiting time period required before you can count all
      visible particles in the counting cell.

 1. A 50 ft. circular stack was sampled over a period of 2 hours.
    At time of sampling the average stack temperature was measured
    to be 180 F.  The stack air (including contaminants) was sampled
    by a dry gas meter at a flowrate of 6.0 cfm and a meter indicated
    temperature of 100 F.  The pressure in the stack was 80% of
    1.2 atm., the pressure, at the site of sampling.  The orifice
    meter used indicated a pressure drop of 8" H2O across the system.
    The volume of the liquid collected in the impinger was measured
    to be 10 ml.  The stack was made of concrete and has a cross
    sectional diameter of 6 ft.  Determine the sampling kinetics and
    state all your recommendations.
    The average velocity in the stack, collected from 20 samples, was
    calculated to be 45 ft/second.
 2. Calculate the CVT for a chemical that has a known analytical
    coefficient of variation of 0.085.  The chemical was sampled by
    a pump having air moving capacity of 37 l/minute.
 3. The 8 hour exposure standard (TLV) for a substance is 85 ppm.
    An integrated sample was taken to determine compliance; the
    following results were obtained:
         Xi (ppm)      ti (min.)
            95            130
           100            240
            88            110
    With 90% confidence, determine whether or not there was any
    compliance given that the analytical coefficient of variation for
    this substance is the same as that for the pump used for sampling.
 4. With 95% confidence, determine the sample size (n) for a
    target population of 75 workers with 10% at risk.