10.20 A certain drying process produces 5 cubic feet of ethanol vapors per hour. If general exhaust ventilation is used, calculate the flow in cubic feet per hour needed to keep the ethanol vapors within OSHA limits. What is another name for ethanol? 10.21 For each of the following materials, suggest substitutes that are feasible for some operations and that prevent certain hazards: Silica (for blasting) (a) (b) Lead-based paint (c) Freon (as a propellant) (d) Acetylene (for welding) 10.22 What problem frequently develops with ventilation filter alarms that indicate pressure differential across the filter? 10.23 What is the purpose of using a heat exchanger for makeup air? What is the disadvantage of this approach? 10.24 If the air outside is at substantially higher pressure than the air inside the plant, what ventilation problem probably exists?