OSH 626, Industrial Hygiene Sampling Strategies

``` AIR SAMPLING ANALYSIS
OSH 626, HOMEWORK SET #1

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.```
```
AIR SAMPLING ANALYSIS
OSH 626, HOMEWORK SET #2

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 a
certain gas at a velocity of 0.545 cm/second.
Calculate,
a) the viscosity of this gas.
b) Reynolds # if the density of the gas is 0.001 gm/cc.

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?
Given:
- 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
and,
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
projected in air at a velocity of 10 cm/sec.  STATE ALL YOUR
ASSUMPTIONS IF ANY.

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.```
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AIR SAMPLING ANALYSIS
OSH 626, HOMEWORK SET #3```
``` 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.```
```
AIR SAMPLING ANALYSIS
OSH 626, HOMEWORK SET #4

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.

CALCULATE:
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.
USE ARITHMETIC-PROBABILITY GRAPH PAPER FOR THIS PART.
d. The waiting time period required before you can count all
visible particles in the counting cell.```
```
AIR SAMPLING ANALYSIS
OSH 626, HOMEWORK SET #5

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
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.```
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