The permissible exposure limits (PELs) for benzene vary depending on the source and duration of exposure [1].

Here are some of the limits specified in the documents:

• OSHA PEL: TWA (Time-Weighted Average) of 1 ppm, STEL (Short-Term Exposure Limit) of 5 ppm [1]
• ACGIH TLV: TWA of 0.5 ppm, STEL of 2.5 ppm [1]
• NIOSH: TWA of 0.1 ppm, STEL of 1 ppm [1]
• Mexico OEL (TWA): 0.5 ppm, STEL: 2.5 ppm [1]

It's important to note that some earlier OSHA PELs have been vacated but are included for reference: TWA of 10 ppm, Ceiling of 25 ppm, STEL of 50 ppm, and Ceiling of 25 ppm [1].

It is important to adhere to the most current and locally applicable exposure limits and to implement appropriate safety measures, such as using a chemical fume hood and wearing personal protective equipment, to minimize benzene exposure [1].