In a semiconductor manufacturing operation, isopropyl alcohol is used to clean parts. There are 100 workstations and each one uses 1 pint of isopropyl alcohol per day. What level of dilution ventilation is needed to keep the air concentrations below the PEL of 400 ppm? (MW =60.1 g/mole; density = 0.79 g/cc; K = 3)

Calculate pounds per minute

lbs/min 057.0

454

179.0

1

10

1

79.3

pt 8

gal 1

min 60

hr 1

hrs 24

day 1

day-station

pt 1stations 100min / lb

3

g

lb

cc

g

L

cc

gal

L

Plug in the formula

cfm 27534001.60

310057.0387

OELMW

10minlb387

CFM

6

6

K

Time-weighted average

• Find the time-weighted average for the following:

Time 8 – 10:30 10:30 – 12:00

12 – 3:15 3:15 – 4:00

Conc 100 ppm 125 ppm 75 ppm 50 ppm

PEL for toluene is 376 mg / M3; is TWA above PEL? (MW = 92 g / mole)

TWA Solution

3mg/M 33824.5

9289.8ppm

ppm 8.89hrs 8

0.75hrs50ppm3.25hrs75ppm1.5hrs125ppm2.5hr100ppmTWA

Decible Addition

• Sum decibel readings of 85 dBA, 87 dBA, 87 dBA, 90 dBA

• For the sum, what is the exposure time allowed under the OSHA PEL?

Decibel solution

hrs6.41.74

hrs 8

2

hrs 8T

dBA 94 10)by multiply log, (take

1322029977282.2713825032318602233

10101010

59094

97.87.85.8

Final Problem Set

• Here is the final problem set. It looks like the one I uploaded earlier did not print out correctly. Use this one – there are only 3 problems.

• I will put up some more, if I have time.