Intro. To Risk Analysis, Fall 2001

a) A solvent is released at a rate of E g/min in a room of volume V ft³. The ventilation rate of the room is k air changes per minute. What equation describes the r rate of change of the concentration of the solvent in the air of the room? What equation describes the concentration as a function of time?

b) What is the steady-state (equilibrium) concentration of the solvent in the air? How long does it take to reach 90% of the steady -state concentration? How does this compare with the time to reach 99% of the steady-state concentration?

c) One person interviewed in a study of users of methylene -choloride based paint strippers said he applied about 12 oz. of the stripper in a 40 minute period in an 8' X 13' X 9.5' kitchen with doors and windows open (but no fan). The air exchange rate for this situation is about 1.5 ACH. What was the maximum concentration of methylene chloride to which he was exposed in this period? What was his maximum rate of inhalation of methylene chloride? What was the cumulative amount to which he was exposed? (A typical breath rate is 8.3 liters of air per minute.)

d) In 1996, the Occupational Safety and Health Administration (OSHA) reduced the limits on occupational exposure to methylene chloride from 500 to 25 parts per million of workplace air for 8-hour shifts and 40-hour work weeks. The current short-term exposure limit (STEL) is a 125 ppm time average over 15 minutes. How do the above concentrations of methylene chloride compare with the OSHA standards? (At standard conditions of pressure and temperature, (P=1 atm, T=273 K), one mole of any pure gas will fill a volume of 22.4 l. One mole of a chemical is the amount of the substance that has a weight in grams numerically equal to the molecular weight of the substance. The molecular weight of methylene chloride is 85.)