IAQ Website of the Month

Occupational Exposure Limits

Each month we publish a newsletter titled IAQ Website of the Month.  The excerpt below was originally published in the October 2013 newsletter.

OSHA uses Permissible Exposure Limits (PELs) to regulate worker exposure to airborne contaminants. Many of its PELs are “outdated and inadequate for ensuring protection of worker health”.  That’s a quote from OSHA itself, not some opinionated blogger!

Most of the current PELs are state of the art… for 1968.  Admittedly, it’s hard to jump through all the hoops required to update PELs.  The lack of updates hasn’t hindered other organizations from incorporating the latest research, technology and experience.  OSHA has now created a list of its “outdated” PELs with side-by-side comparisons to the following occupational exposure limits:

  • American Conference of Governmental Industrial Hygienists (ACGIH®) Threshold Limit Values (TLVs®)
  • National Institute for Occupational Safety and Health (NIOSH) Recommended Exposure Limits (RELs)
  • California Division of Occupational Safety and Health (Cal/OSHA) Permissible Exposure Limits (PELs)

Now you don’t need to thumb through four different publications to see the various occupational exposure limits.  The coolest part? In the past, you needed to purchase the TLVs® each year from the ACGIH®.  Now OSHA gives them to you for free.

Note the difference between occupational exposure limits for two common IAQ contaminants:


  • OSHA PEL: none
  • ACGIH® TLV®: 0.3 ppm ceiling
  • NIOSH REL: 0.016 ppm up to 10-hour TWA (carcinogen), 0.1 ppm 15-minute ceiling
  • Cal/OSHA PEL: 0.75 ppm 8-hour TWA, 2 ppm short term

Carbon monoxide

  • OSHA PEL: 50 ppm 8-hour TWA
  • ACGIH® TLV®: 25 ppm 8-hour TWA
  • NIOSH REL: 35 ppm Up to 10-hour TWA, 200 ppm ceiling
  • Cal/OSHA PEL: 25 ppm 8-hour TWA, 200 ppm ceiling

To view the entire list of chemicals, visit this month’s featured website: OSHA’s Annotated PELs.

Please note: occupational exposure limits are not designed to be protective of the entire population.  In our classes you will learn about other, more protective exposure guidelines.


Permissible Exposure Limits, an IAQA Tech Tip Video

If you cannot view the video above go to

Industrial Hygiene

Contaminant Exposure Limits

While traveling this week, I read read through October’s Synergist magazine.  For those of you not familiar with The Synergist, it is a publication produced by the American Industrial Hygiene Association (AIHA).

This month’s edition had two excellent articles regarding exposure limits.  What are exposure limits?  Simply put, these are concentrations of contaminants to which people should not be exposed.  Some exposure limits are enforceable by law and others are mere recommendations.  Some exposure limits apply to the entire population, and others are for healthy workers in an occupational setting.  No two organizations promulgating exposure limits are the same.  Below are the most commonly quoted exposure limits in the US: