Here is a collection of problems, many from previous examinations.  Work through as many of these as you can.  We will review as many as possible in class.   The exam itself will likely have fewer problems than this.  Refer to the equation sheet  or lab notebook for formulas.  All formulas needed will be provided with the exam.

 

1.         What volume of liquid hexane (MW = 86.19 g/mole, density = .6603 g/cc) must be injected into a volume of 100 L of air to generate a hexane concentration of 75 ppm? P = 765 mm Hg, T = 21 degrees C

 

2.         An air-sampling pump is used to collect three samples.  The pump is pre-calibrated at 2.2 liters per minute and post-calibrated at 2.1 liters per minute.  From the following information, calculate the 8-hour time-weighted average dust concentration observed.  Ignore the lunch break in your calculations.

 

Time on:        8:00                12:00              3:00

Time off          11:00              3:00                5:00

Filter initial     84.34              84.72              84.27     (mg)

Filter final       86.17              87.00              85.99     (mg)

 

3.         If the concentration of isopropanol is reported as 232 mg/M3, what is this in ppm? (3 points)

 

4.         A 2.5 Lpm flow of air containing 100 ppm toluene is introduced into a 25 liter container.  What is the concentration in the container after 30 minutes?  If clean air is then introduced, at a flow of 3 Lpm, what is the concentration of toluene in the container after an additional 30 minutes?

 

5.         If the sensitivity of a balance is 20 micrograms, and the estimated air concentration of a dust is 2.9 mg/M3, what is the minimal sample time for a flow rate of 2.5 Lpm? 

 

6.         Convert 27 cubic feet to liters.

 

8.         The correction factor for methane on a combustible gas meter is 0.42.  If the meter reads 75 % LEL, what is the true % LEL?

 

9.         The LEL for hexane is 1.2 %.  If the corrected meter response if 8 % LEL, what is the hexane concentration, in ppm?

 

10.       The data below come from a cascade impactor analysis of dust levels.  Use log-probability paper to find mass median aerodynamic diameter (MMAD) and its geometric standard deviation (GSD).

 

Stage              Dae                   Mass collected

F                      0.26                0

8                      0.52                0.1

7                      0.93                0.3

6                      1.55                0.4

5                      3.5                   0.5

4                      6.0                   0.2

3                      9.8                   0.1

2                      14.8                0

1                      21.3                0                     

 

11.       The vapor pressure of m-xylene at 28.3 degrees Celsius is 10 mm Hg.  What is the saturation vapor concentration, in ppm and in mg/M3?

 

 

12.       Consider the laboratory data below.  Calculate the 8-hour time-weighted average exposure for these three samples.

 

Front section (mg)

Back section (mg)

Reported flow rate (ml/min)

Reported sample duration (min)

1.85

.12

200

240

2.07

.19

200

120

1.23

.05

200

120

Field blank had total of 0.02 mg

Note: desorption efficiency: 99 %

 

13.    If a combustible gas indicator shows a reading of 15 % LEL toluene, what is this concentration, in ppm? (The LEL for toluene is 7.1 %)

 

14.  A 2.5 Lpm flow of air containing 100 ppm toluene is introduced into a 23.5 liter container.  What is the concentration in the container after 30 minutes?  If clean air is then introduced, at a flow of 3 Lpm, what is the concentration of toluene in the container after an additional 30 minutes?

 

15. An asbestos counting report indicates that 175 fibers were counted in 60 fields.  If the graticle area is 0.00785 mm2, the effective filter area is 385 mm2, the sample time is 6 hours, and the sample flow rate is 2 liters per minute, calculate the 8 hour time weighted average exposure to asbestos fibers.  The time period not sampled had zero exposure to asbestos.