Several organizations publish occupational exposure limits (OELs) including the Occupational Safety and Health Administration’s (OSHA) permissible exposure limits (PELs), the American Conference of Governmental Industrial Hygienists’ (ACGIH) threshold limit values (TLVs), and the National Institute for Occupational Safety and Health’s (NIOSH) recommended exposure limits (RELs). Only OSHA’s PELs are legally enforceable. Discuss why you would only use the OSHA PEL at a facility where you were the safety officer, or alternatively, why you would choose to use one of the other OELs or a combination of the OELs.
UNIT V STUDY GUIDE
Applying the Data From Exposure
Assessments to Existing
Occupational Exposure Limits
Course Learning Outcomes for Unit V
Upon completion of this unit, students should be able to:
2. Discuss industrial hygiene related standards.
2.1 Identify the different organizations that publish industrial hygiene occupational exposure limits
(OELs).
2.2 Compare and contrast different OELs.
6. Evaluate exposure to workplace hazards utilizing published occupational exposure levels
6.1 Determine which occupational exposure limits (OELs) should be used in evaluating sampling
data.
6.2 Assess acceptable levels of risk based on sampling data and existing occupational exposure
limits (OELs).
Reading Assignment
Chapter 5: Occupational Exposure Limits and Assessment of Workplace Chemical Risks, pp. 95–111
In order to access the following resources, click the links below.
Read the introduction on pp. vii–xvi and Chapter 1: Recommendations for a Noise Standard on pp. 1–10 of
the Criteria for a Recommended Standard: Occupational Noise Exposure linked below.
Centers for Disease Control and Prevention. (1998). Criteria for a recommended standard: Occupational
noise exposure (DHHS [NIOSH] Publication No. 98-126). Retrieved from
https://stacks.cdc.gov/view/cdc/6376
Occupational Safety and Health Administration (OSHA) is the only organization that issues occupational
exposure limits (OELs) for airborne exposures that are legally enforceable. The following link takes you to the
air contaminants section of the Code of Federal Regulations (CFRs) containing OSHA’s standard for
permissible exposure limits (PELs) for compounds that do not have a chemical-specific standard established.
Most industrial hygienists use Table Z-1 of this regulation more than any other section.
Occupational Safety and Health Administration. (1970). Occupational safety and health standards: Toxic and
hazardous substances (Standard No. 1910.1000). Available at https://www.osha.gov/lawsregs/regulations/standardnumber/1910/1910.1000
Waters, M., McKernan, L., Maier, A., Jayjock, M., Schaeffer, V., & Brosseau, L. (2015). Exposure estimation
and interpretation of occupational risk: Enhanced information for the occupational risk manager.
Journal of Occupational and Environmental Hygiene, 12(Suppl. 1), S99–S111. Retrieved from
https://libraryresources.columbiasouthern.edu/login?url=http://search.ebscohost.com/login.aspx?direc
t=true&db=a9h&AN=111071555&site=ehost-live&scope=site
Unit Lesson
You have now calculated the exposure results from the sampling. What do you do next? For most individuals,
the answer would be, “Compare the results to the OSHA PEL.” Indeed, that is what most individuals do. A
problem that can arise is knowing which limits you compare the results to because there are many competing
limits and the differences in the limits can be severe.
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Occupational Exposure Limits
UNIT x STUDY GUIDE
Title
Your first inclination is probably to compare the results to the permissible exposure limits (PELs) published by
the Occupational Safety and Health Administration (OSHA). After all, they are the only occupational exposure
limits (OELs) that are legally binding. In other words, employers are required by law to reduce exposures for
some chemical hazards to a level below the OSHA PEL. If exposures are not reduced to less than a
published PEL, OSHA has the authority to issue citations and impose penalties. This provides a great
incentive for employers to use the OSHA PELs. In fact, most employers primarily use the OSHA PELs when
utilizing sampling results.
OELs are used by industrial hygienists to evaluate the risk of illness or death for worker exposures. In
essence, we are performing a risk assessment using the sampling results for the severity variable in the risk
assessment matrix. OSHA evaluated multiple scientific studies concerning health risks prior to establishing a
PEL. Therefore, one could assume that a PEL represents an acceptable level of risk. In many of the
discussions for PELs, OSHA includes a discussion of acceptable risk as it related to the choice of a PEL.
Over the years OSHA has used some specific levels of risk as being acceptable.
One example would be the level of risk that OSHA considers acceptable for death in workers exposed to a
compound. Historically, OSHA has used the risk of 1 death in 1,000 workers exposed to a chemical for eight
hours a day for a working lifetime (45 years) as an acceptable risk (“OSHA Occupational,” 2016). This level of
risk has been upheld in court decisions. This may lead you to believe that all OSHA PELs reduce the risk of
death to less than 1 in 1,000. However, this would be inaccurate because of the requirements placed on
OSHA in setting PELs.
Evaluating Risk and OELs
OSHA is required to reduce significant risk when establishing PELs, but only to the extent feasible. In
evaluating feasibility, OSHA must evaluate both technological and economic feasibility (“OSHA Occupational,”
2016). This means that OSHA has to look to see if industries affected by the PEL have the technical means to
reduce exposures to the new PEL and also how much economic impact the reduction would have on the
industries. For these reasons, some PELs do not reduce risk to a level that OSHA would consider acceptable.
One example would be the recent reduction of the PEL for respirable crystalline silica. The lifetime risk for
death from lung cancer under the old PEL was 20-26 deaths per 1,000 workers. With exposures to the new,
reduced PEL the lifetime risk was estimated to 16-23 deaths per 1,000 workers, and for the new action level,
the lifetime risk was 10-21 deaths per 1,000 workers (“OSHA Occupational,” 2016). These levels are
obviously greater than the risk levels OSHA considers significant. They were not set lower because of
feasibility issues. Another significant issue is that many of the OSHA PELs are based on scientific data from
the 1960s and 1970s and have not been updated to reflect findings from more recent studies.
The American Conference of Governmental Industrial Hygienists (ACGIH) is a not-for-profit, nongovernmental
organization. The ACGIH is not required to consider feasibility when establishing their OELs. These OELs are
health-based guidelines (ACGIH, n.d.). This means that the ACGIH can set or reduce their guidelines based
on scientific research without considering the feasibility of employers using the OELs. This has resulted in
many threshold limit values (TLVs) being much lower than the corresponding OSHA PEL.
ACGIH Guidelines
The ACGIH publishes several guidelines for which OSHA has limited requirements. One is called biological
exposure indices or BEI (ACGIH, n.d.). BEIs are guidelines for assessing worker exposures to chemical
hazards through biological monitoring. In other words, a biological sample is collected, typically urine or blood,
and is analyzed for some biological indicator based on a knowledge of how the chemical is metabolized in the
body. The result is then compared to a BEI to evaluate exposures. While the TLVs are based on the amount
of a chemical in the air or the potential exposure, the BEI represents the amount of the chemical uptake into
the body (ACGIH, n.d.). Biological sampling can be used to account for the differences in individual reactions
to exposure. An example would be the collection of a urine sample at the end of a work shift and analysis for
mandelic acid and phenylglyoxylic acid to evaluate exposure to ethyl benzene (ACGIH, n.d.). OSHA typically
only has requirements for biological monitoring for very few compounds in chemical specific standards and
only requires the biological monitoring when exposures exceed a certain level for a specified period of time.
Lead in blood monitoring is one example in 29 CFR 1910.1025 (OSHA, 1970).
OSH 6302, Advanced Industrial Hygiene
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UNIT x STUDY GUIDE
The ACGIH also publishes several guidelines for physical hazards. One that isTitle
used fairly extensively by
health and safety professionals is for thermal stress. While the guidelines are designed for both cold stress
and heat stress, the guidelines for heat stress are more widely used. If you are familiar with the guidelines,
you have heard of the wet bulb globe temperature (WBGT) readings that are used to determine a
recommended work/rest regimen (ACGIH, n.d.).
The ACGIH (n.d.) also has TLVs for noise exposures. In this area, the ACGIH is much more conservative
than OSHA. OSHA has established an eight-hour time-weighted average or TWA PEL for the noise of 90
decibels on the A scale (dBA). OSHA also established an action level of 85 dBA for an eight-hour shift or an
equivalent exposure of 50%. OSHA’s permissible exposure time changes as the noise exposure changes.
OSHA has adopted a 5 dB doubling criteria. This means that for every 5 dB that the noise increases, the
allowable exposure time is cut in half. For example, if the TWA exposure increases from 90 dBA to 95 dBA,
the exposure is only allowed for four hours. The ACGIH has set a guideline of 85 dBA for its TLV and uses a
3 dB doubling criteria. Thus, if the personal TWA exposure increases from 85 dB to 88 dBA the allowable
exposure decreases to four hours. The differences may not seem that great but remember the dB scale is
logarithmic, not linear so a change of 3 dB or 5 dB is greater than you would think.
The National Institute for Occupational Safety and Health Recommended Exposure Limits
The National Institute for Occupational Safety and Health (NIOSH) is a government agency within the Centers
for Disease Control and Prevention (CDC). One task NIOSH performs is conducting research and making
recommendations to OSHA for OELs. The OELs that NIOSH publishes are called recommended exposure
limits (RELs). As the name implies, the RELs are recommended guidelines and not legally enforceable (CDC,
n.d.). Since NIOSH is not required to perform feasibility studies, the RELs are also, generally, lower than the
OSHA PELs.
American Industrial Hygiene Association Guidelines
One other group that publishes OELs that are sometimes used by industrial hygienists is the American
Industrial Hygiene Association (AIHA). The AIHA is a not-for-profit, nongovernmental organization. The AIHA
(n.d.) publishes two basic OELs, Emergency Response Planning Guidelines (ERPGs) and Workplace
Environmental Exposure Levels guides (WEELs). ERPGs are guidelines developed for emergency responses
to catastrophic releases and not for routine exposures in workplaces. WEELs are developed for occupational
exposures and are designed to represent a level that is protective for most workers. Many of the WEELs are
for chemicals for which there are no OELs established by OSHA, the ACGIH, or NIOSH.
Deciding Which OEL to Use
How do you make up your mind about which OEL to compare your results with? The first step typically
involves a review of your company’s policy. Some companies will have a policy that only the legally binding
OSHA PELs will be used. Other companies have policies that all OELs will be reviewed, and the most
conservative limit will be used. This goes to a discussion of what is legally required and what is industrial
hygiene best practices. Best practices would dictate that you use the most conservative OEL available and is
the choice of most IHs. Sometimes the most difficult job an industrial hygienist has is convincing management
of the benefits of using a TLV instead of a PEL.
Another variable that must be considered when comparing sample results to OELs is the inherent error that
we know is present in the sample results. We discussed this error in a prior unit. Because there is an error in
the sample results, when you receive sample results that are close to a published OEL, you cannot be sure
that the actual exposure exceeds the OEL. Ideally, you would want to take multiple samples and then perform
a statistical analysis of all the results. Many industrial hygienists will then look at the 95th percentile result and
compare that to the OEL. This gives you more confidence that the actual exposure does or does not exceed
the OEL. The AIHA (n.d.) website has a spreadsheet industrial hygienists can use to conduct the statistical
analysis. The spreadsheet works well when you have a lot of data.
Unfortunately, most occupational settings do not have hundreds of workers performing the same task. In
many cases, you may have only one individual performing a task with potential exposure to a specific
chemical hazard. You are then forced to make decisions about exposures based on a limited number of
OSH 6302, Advanced Industrial Hygiene
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samples. What are your options? One approach is to compare the exposure toUNIT
50%xofSTUDY
the OEL.
For some
GUIDE
chemicals, OSHA uses this approach to establish an action level. These action
levels are typically set for
Title
compounds for which OSHA has promulgated a chemical-specific standard, such as lead (OSHA, 1970).
When an industrial hygienist uses 50% of the OEL for other chemical hazards as an action level, the worker is
provided with additional protection.
In the end, the industrial hygienist must make some decisions about sample results and OELs based on
professional judgment and experience. Sometimes this involves an understanding of the toxicity of the
compounds as we discussed in a previous unit. For example, if you have a sample result that is close the
OEL and you know that the compound has high toxicity, either acute or chronic, you may decide to use 50%
of the most conservative OEL available. If you know the compound has fairly low toxicity, you may decide to
be more liberal in your choice of OELs.
References
American Conference of Governmental Industrial Hygienists. (n.d.). TLV/BEI guidelines. Retrieved from
https://www.acgih.org/tlv-bei-guidelines/policies-procedures-presentations/overview
American Industrial Hygiene Association. (n.d.). Books: AIHA hazard recognition and evaluation. Retrieved
from https://onlineams.aiha.org/amsssa/ecssashop.show_category?p_category_id=HAZARDRECEVAL&p_cust_id=&p
_order_serno=&p_promo_cd=&p_price_cd=&p_session_serno=16018293&p_trans_ty=
Centers for Disease Control and Prevention. (n.d.). About NIOSH. Retrieved from
https://www.cdc.gov/niosh/about/default.html
Occupational Safety and Health Administration. (1970). Occupational safety and health standards: Toxic and
hazardous substances (Standard No. 1910.1025). Retrieved from https://www.osha.gov/lawsregs/regulations/standardnumber/1910/1910.1025
OSHA Occupational Exposure to Respirable Crystalline Silica, 81 Fed. Reg. 16286 (Mar. 25, 2016).
Available at https://www.govinfo.gov/content/pkg/FR-2016-03-25/pdf/2016-04800.pdf
Suggested Reading
In order to access the following resources, click the links below.
The CSU Online Library contains many articles that relate to the Unit V readings. The following are just a few
of the related articles that can be found in the Academic Search Complete database.
Occupational Safety and Health Administration (OSHA) and the American Conference of Governmental
Industrial Hygienists (ACGIH) have two relatively different occupational exposure limits (OELs) for noise.
They are only 5 dBA different, but because the dB scale is lognormal, not linear, a difference of 5 dB
represents a doubling of the sound pressure. The following article shows how one group of researchers
compared noise sampling results to both the OSHA permissible exposure limit (PEL) and the ACGIH
threshold limit values (TLV), especially not the differences in the reported sampling results when the
dosimeters are set to the OSHA and ACGIH parameters.
Gilbertson, L. R., & Vosburgh, D. J. H. (2015). Patrol officer daily noise exposure. Journal of Occupational
and Environmental Hygiene, 12(10), 686–691. Retrieved from
https://libraryresources.columbiasouthern.edu/login?url=http://search.ebscohost.com/login.aspx?direc
t=true&db=a9h&AN=109440687&site=ehost-live&scope=site
The following article demonstrates the anticipation, recognition, and evaluation process from start to finish at
an auto collision repair shop. The sampling involved several examples of IH sampling. Review how the results
were compared to OSHA PELs and ACGIH TLVs and the discussion of how some results were less than the
OSHA PEL but exceeded the ACGIH TLV.
OSH 6302, Advanced Industrial Hygiene
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UNIT x STUDY GUIDE
Bejan, A., Brosseau, L. M., & Parker, D. L. (2011). Exposure assessment in auto
collision repair shops.
Title
Journal of Occupational and Environmental Hygiene, 8(7), 401–408. Retrieved from
https://libraryresources.columbiasouthern.edu/login?url=http://search.ebscohost.com/login.aspx?direc
t=true&db=a9h&AN=75127947&site=ehost-live&scope=site
The following article is another good example of the entire sampling, analytical, and evaluation process. In
this case, the researchers were looking at exposures to various aldehydes that were off-gassing from wood
pellets. Read through the article to review the process. Note that the article includes photos showing how the
sampling was performed, a copy of one of the GC runs showing how the analytical peaks look, and a
comparison to the existing OELs. Especially look at Figure 8 which is a good comparison of how the different
OELs can vary.
Rahman, M. A., Rossner, A., & Hopke, P. K. (2017). Occupational exposure of aldehydes resulting from the
storage of wood pellets. Journal of Occupational and Environmental Hygiene, 14(6), 417–426.
Retrieved from
https://libraryresources.columbiasouthern.edu/login?url=http://search.ebscohost.com/login.aspx?direc
t=true&db=a9h&AN=123086666&site=ehost-live&scope=site
Learning Activities (Nongraded)
Nongraded Learning Activities are provided to aid students in their course of study. You do not have to submit
them. If you have questions, contact your instructor for further guidance and information.
The Occupational Safety and Health Administration (OSHA) publishes established permissible exposure limits
(PELS) for most chemicals in three tables (Z-1, Z-2, and Z-3) that are appendices to the standard 29 CFR
1910.1000. Access Table Z-1 at
https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.1000TABLEZ1.
Look for chemicals with which you are familiar. Can you determine anything about the risk of a chemical by
reviewing OSHA’s PELs in the table?
OSH 6302, Advanced Industrial Hygiene
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