Question

permissible exposure limit (pel) is dropdown for an 8 hour day and dropdown for a 12 hour day.

short term exposure limit (stel) is dropdown for any 15 minute period during the day with dropdown minutes between exposures and no more than 4 exposures in an 8 hour day.

Explanation:

Identify standard regulatory limits

Using the Chemical Toxicology knowledge point, we recall the OSHA occupational exposure limits for benzene (29 CFR 1910.1028). The standard Permissible Exposure Limit (PEL) is \(1\text{ ppm}\) as an 8-hour time-weighted average (TWA).

Adjust for extended shifts

For a 12-hour workday, the exposure limit must be adjusted to maintain equivalent cumulative exposure. Under standard OSHA model adjustments (such as the Brief and Scala model), the PEL is reduced to \(0.5\text{ ppm}\) for a 12-hour shift.

Determine short-term limits

The OSHA Short Term Exposure Limit (STEL) for benzene is \(5\text{ ppm}\) averaged over any 15-minute period.

Find minimum rest periods

According to standard industrial hygiene guidelines, STEL exposures must be spaced by at least \(60\text{ minutes}\) of clean air between exposures, with a maximum of 4 exposures per 8-hour day.

Answer:

Question 1

Permissible Exposure Limit (PEL) is <blank>\(1\text{ ppm}\)</blank> for an 8 hour day and <blank>\(0.5\text{ ppm}\)</blank> for a 12 hour day.

Question 2

Short Term Exposure Limit (STEL) is <blank>\(5\text{ ppm}\)</blank> for any 15 minute period during the day with <blank>\(60\)</blank> minutes between exposures and no more than 4 exposures in an 8 hour day.