TLVs® (Threshold Limit Value) and BEIs® (Biological Exposure Indices) are often recognized as “safe levels” for worker exposures to chemical substances and physical agents. ACGIH®, a non-profit scientific association, develops and annually summarizes TLVs® and BEIs® in a booklet (2019 booklet is about 300 pages) available at Proper application of TLVs® and BEIs® are essential to today’s practice of industrial hygiene (IH). 


TLVs® originated in the 1930s. TLVs® are intended for voluntary guidance but often find their way into regulations. OSHA’s first PELs, for example, were derived from ACGIH’s 1968 TLVs® list. OSHA’s 2012 HazCom standard requires that voluntary TLVs®, along with mandatory OSHA PELs, must be included on applicable Safety Data Sheets.

Economic or technical feasibility are not considered in the development of TLVs® and BEIs®. TLVs® and BEIs® are based solely on health factors. TLVs® and BEIs® are not intended as legal standards but are used voluntarily in the practice of IH when “interpreted and applied only by a person trained in this discipline,” per ACGIH® policy statement.

Pressure to use TLVs® may come from non-regulatory sources. Welding consumables, such as weld wire or rod, for example, from suppliers such as Lincoln Electric, now include lung and sinus cancer warnings on product containers with mention of “ACGIH 2018 update” regarding hexavalent chromium. Reference to ACGIH® updates (revised TLVs®) on product containers is not required by OSHA but may address product liability -- “failure to warn” concerns -- such as those that sparked welding fume mass tort litigation back in 2003.  Lincoln Electric advises users of their products to control weld fume exposure to “the TLV or applicable regulatory exposure limit standard, whichever is the more conservative.” 

Noise example

TLVs® have evolved to address many IH hazards including noise, electromagnetic fields, ionizing and non-ionizing radiation, ergonomics, heat and cold stress, microbiological agents, just to name a few. These and other IH hazards are summarized in the annual TLVs® and BEIs® booklet.

TLVs® for chemicals is the most popular use; second is probably TLVs® for noise (audible sound). OSHA’s PEL for noise is based on a 5-dB doubling average that begins at 90 dBA TWA for 8 hours.  When 5 dB is added to 90 dBA the permissible time at that exposure is reduced by one-half. For example, the permissible time at 95 dBA is 4 hours, 100 dBA is 2 hours and 105 dBA is one hour. Continue the table in this manner even into the minutes or seconds.

TLVs® for noise are based on a 3-dB doubling average that begins at 85 dBA TWA for 8 hours. When 3 dB is added to 85 dBA the permissible time at that exposure is reduced by one-half. The allowable time at 88 dBA is 4 hours and 91 dBA is 2 hours. Continue the noise TLVs® table into the minutes or seconds, then compare with the noise PEL table created above. Dramatic differences appear at the higher dBAs. OSHA’s permissible time at 115 dBA is 15 minutes while the TLV is 28.12 seconds. The TLV at 130 dBA is 0.88 seconds!

OSHA requires a hearing conservation program, e.g. annual hearing tests at 85 dBA 8-hr. TWA. Using TLVs®, what level of noise exposure should employers use to establish a hearing conservation program? This is where the judgment from a professional industrial hygienist comes into play. When considering TLV® guidance, an industrial hygienist may consider many things, including the accuracy of noise measurements, whether workers are exposed to ototoxic chemicals such as carbon monoxide, styrene, and toluene, to name a few, to the presence of infrasound and low-frequency sound not initially measured with a dosimeter and even whether the worker is pregnant.

Judgment calls

The involvement of a person trained in IH discipline, judgment of an industrial hygienist, and professional industrial hygienist’s interpretations and applications are referenced throughout ACGIH® TLVs® and BEIs® booklet. Language is technical and often described by formulas, charts and tables that may appear gibberish to those not trained in IH.

What is not defined in the booklet is how much IH training is enough to interpret and apply booklet information, what constitutes valid IH judgment, and who is considered a professional IH? The hallmark of IH individual technical competency is the ABIH® Certified Industrial Hygienist® or CIH®. These terms are not referenced in the TLVs® or BEIs® booklet. Professionalism is often ascribed to those who have a license to practice. IH has yet to reach this pinnacle. Lack of credentials should not disqualify someone from having IH competency. 

Importance of TLVs® and BEIs® booklet

People who say they’re competent in IH are competent – until proven otherwise. Abuse of IH information often begins with someone misinterpreting and misapplying TLVs® and BEIs® information.

It’s not uncommon for me to encounter OHS pros who claim IH knowledge and then misapply and confuse the PELs and TLVs® for noise. That’s one reason I partially broke down the noise explanation above – to try to draw clarity with a basic explanation. 

TLVs® are respected and are conservatively used by many organizations including some regulatory agencies within and outside the United States.  TLVs® are not gospel. TLVs® are true to the extent that documentation (available from ACGIH® and other sources) scientifically supports the information as interpreted and applied by someone trained in the discipline of IH.

I’m a traditionally trained industrial hygienis who was taught information in the TLVs® booklet that began with my undergraduate schooling, years before actually beginning my IH practice. The TLVs® booklet, usually the latest annual edition, is the top essential reference used in my IH practice.

Thoroughly review all the information provided in the TLVs® and BEIs® booklet and determine where you have knowledge or awareness gaps - then fill those gaps as appropriate.