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Recommendations for Controlling Hazards As the environmental health...

Recommendations for Controlling Hazards

As the environmental health and safety (EHS) manager, i have been asked to evaluate an existing operation to determine employee's current exposure to hexane, which is a chemical used in painting processes.


i am to complete an evaluation of the employee's current exposure by determining the employee's exposure to hexane (toxic contaminant) by calculating time-weighted average (TWA) and compare it to the permissible exposure limit (PEL) and modify the PEL, if necessary.


i cant figure out the math



An employee working in a room measuring 15 ft x 20 ft x 15 ft sprays paint assembly parts using a paint containing hexane. The PEL for hexane is 500 ppm. The employee wears a half-face, air-purifying respirator, but management would like to install engineering control measures to reduce or eliminate the employee's exposure to hexane. The options are to:

(1) install a dilution ventilation system, or
(2) install a local exhaust ventilation system.

The employee works a 9-hour shift and has the following exposures:

Image transcription text

Sample No. Concentration Sampling Time 550 ppm 1.5 hours 2 400 ppm 5.8 hours 3 375 ppm 1.7 hours

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For the general dilution ventilation system to work, there must be at least 20 room air changes per hour. The fan which supplies air to this area produces 1,500 cubic feet per minute (cfm) (Q).

In order for the local exhaust ventilation system to remove the contaminant to acceptable concentrations, the capture velocity must be at least 140 feet per minute (fpm). The proposed local exhaust system ventilation system uses a 1.0 feet diameter duct and a fan that provides a total volume of 1,275 cubic feet per minute (cfm). The source of the contamination is located 1.5 feet from the opening of the duct. Determine the appropriate ventilation control and calculate the capture velocity.

The book im using is safety professionals reference and study guide by w. David yates third addition and page 205 is info on te math






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