Protective Action Criteria - Emergency Exposure Limits

Most of us are aware that there are exposure limits for chemical exposures in the workplace, so called occupational exposure limits (OELs). In the US, the legal exposure limits are in the form of OSHA Permissible exposure limits (PELs) available at 29 CFGR1910.1000 Tbl Z-1. There are several other OELs that are based on scientific data including the NIOSH recommended exposure limits (RELs), the ACGIH threshold limit values (TLVs) and the AIHA’s workplace environmental exposure levels (WEELs).

In addition to OELs, there are also emergency exposure levels.  The main difference between OELs and PAC levels are that OELs are intended for the workplace where one may be safely exposed to this concentration or concentration over time, for eight hours, 5 days a week for a full work life without adverse effects. Emergency exposure levels on the other hand are intended for emergency responders as a tool to assess the risk to people who have had a one time exposure to a chemical.

There are the three main emergency exposure levels in common usage. The EPA has promulgated acute exposure guidelines (AEGLs) and the AIHA has issued Emergency Response planning guidelines (ERPLs). The AEGLs and ERPLs are subdivided based on the impact of an exposure.The AEGL levels are defined as follows:

• AEGL-1 is the airborne concentration, expressed as parts per million or milligrams per cubic meter (ppm or mg/m3) of a substance above which it is predicted that the general population, including susceptible individuals, could experience notable discomfort, irritation, or certain asymptomatic nonsensory effects. However, the effects are not disabling and are transient and reversible upon cessation of exposure.

• AEGL-2 is the airborne concentration (expressed as ppm or mg/m3) of a substance above which it is predicted that the general population, including susceptible individuals, could experience irreversible or other serious, long-lasting adverse health effects or an impaired ability to escape.

• AEGL-3 is the airborne concentration (expressed as ppm or mg/m3) of a substance above which it is predicted that the general population, including susceptible individuals, could experience life-threatening health effects or death.

 The ERPLs are similarly divided, with similar definitions:

• ·ERPG-1 is the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to 1 hr without experiencing other than mild transient adverse health effects or perceiving a clearly defined, objectionable odor.

• ERPG-2 is the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to 1 hr without experiencing or developing irreversible or other serious health effects or symptoms which could impair an individual's ability to take protective action.

• ERPG-3 is the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to 1 hour without experiencing or developing life-threatening health effects.

The main difference between the AEGLs and the ERPGs is the ERPGs are based on a one hour exposure, whereas the AEGLs are calculated for exposures from 10 minutes to 8 hours.

The AEGL and ERPG values can be compared with the NIOSH immediately dangerous to life and health levels (IDLH).

Some values for representative compounds are shown in the table below:

Compound	AEGL 1	AEGL 2	ERPG 1	ERPG 2	IDLH	ACGIH TLV
Ethylene oxide	n/a	45 ppm	n/a	50 ppm	800 ppm	1 ppm 8 Hr TWA
Formaldehyde	1.7 ppm	5.0 ppm	1 ppm	10 ppm	20 ppm	0.3 ppm ceiling
Glutaraldehyde	n/a	n/a	0.2 ppm	1 ppm	n/a	0.05 ppm ceiling
Hydrogen Peroxide	n/a	n/a	10 ppm	50 ppm	75 ppm	1 ppm 8 Hr TWA
Peracetic Acid	0.17 ppm	0.51 ppm	n/a	n/a	n/a	n/a*

Notes: AEGLs based on 60 minute exposure.
        *The ACGIH has proposed a 15 minute STEL for peracetic acid of 0.4 ppm.

As may be expected, the AEGLs and ERPGs are significantly higher than the ACGIH TLVs, since the former apply to a one time exposure in an emergency situation and the latter to occupational exposure, 40 hours a week.

Both the AEGLs and the ERPGs are based on scientific studies; however for many chemicals systematic exposure studies have not been conducted. The last member of the PAC family are the DOE Office of Emergency Operations’ temporary emergency exposure limits (TEELs) developed by SCAPA.

The TEELs are estimates made based on OELs, chemicalproperties, chemical structures, health hazard warnings etc.  The goal behind the TEEL program is to estimate an emergency exposure level based on the information available. The development of a TEEL is not a rigorous as an AEGL or ERPG, but in an emergency situation it is much better to have TEEL guidance than nothing at all. The TEELs are subject to periodic update and TEEL compounds may also rise to the top of the pile and become and AEGL or ERPG.  The TEELs are also divided similarly to the AEGLs and ERPGs into TEEL-1, TEEL-2 and TEEL-3. 

Today there are over 3000 TEELs  compared with about 140 final AEGLs and about 145 ERPGs.

The Emergency Management Special Interest Group (sponsored by the Department of Energy)  combines these emergency exposure limits into Protection Action Criteria (PACs)  to give PAC-1, PAC-2 and PAC-3 as with the AEGLs and the ERPGs.  For any particular chemical, the PAC is based on the following hierarchy of values:

1) Use AEGLs (including final or interim values) if they are available.

2) If AEGLs are not available, use ERPGs.

3) If neither AEGLs or ERPGs are available, use TEELs.

The PAC values are designed for use by first responders and other people dealing with potential chemical exposures in an emergency. The PAC values are available from an on-line database and tabulated in pdf and Excel formats.  

Occupational Exposure Limits in Australia

Every country has its own legal system and within that system its own occupational safety laws. For people not familiar with these laws, finding the relevant occupational exposure limits (OELs) can be time consuming.  This blog recently provided an article with links for readers to find occupational exposure limits in Canada, and compared these to the US OSHA Limits. This article provides similar information for Australia.

Unlike the United States which has a strong federal government and relatively weak states, in Australia the opposite is true. The provinces are considered co-sovereign states with the federal government; and the territories though under the egis of the federal government, also promulgate their own laws. However, all the six states and several territories collaborated through an organization called Safe Work Australia to develop a common set of OELs and a model occupational statute and associated regulations that the states and territories can adopt.


Occupational Exposure Limits
Safe Work has created an on-line database for occupational exposure limits, which allows chemicals to be searched by name or CAS number. The complete list of OELs is also available for download as a pdf. The OEL for some representative compounds are shown below and for the most part they are fairly similar to those used in the US.

                                   Australia              US-OSHA              ACGIH TLV
Ethylene Oxide             1 ppm (8 hr TWA)            1 ppm (8 hr TWA)           1 ppm (8 hr TWA)
Glutaraldehyde            0.1 ppm peak                       n/a                                            0.05 ppm ceiling
Hydrogen peroxide     1 ppm (8 hr TWA)            1 ppm (8 hr TWA)           1 ppm (8 hr TWA)
Ozone                                     0.1 ppm                                  0.1 ppm (8 hr TWA)        0.05 - 0.2 ppm
                                                                                                                                            
Notes: 
1) TWA = time weighted average, peak = ceiling = maximum permissible exposure at any time.
2) Regulations are always subject to change and to the readers should verify that the above information is correct before relying on this information.


Work Safe has also developed a guide on the application of workplace exposure standards for airborne contaminants (exposure standards) in the workplace. 

Occupational Safety Statutes and Regulations
The federal government and all of the states and territories, except for Victoria, have adopted the model statute and regulations. As with most common law countries, the legislature passes a broad act or statute that empowers a government agency to then develop more specific regulations. The statutes and regulations are listed below as a reference but will not discussed further in this article.

Work Health and Safety Act 2011

Model Work Health and Safety Regulations 2011

While Victoria's statute is different from the other states, its occupational laws are generally compatible.

The Victoria Occupational Safety and Health Act of 2004

The Victoria - Occupational Health and Safety Regulations 2007

Occupational Exposure Limits in Canada Compared to the US.

The primary goal of this blog article is to allow readers to easily find exposure data in the US and Canada, by following the links in the text. Hydrogen peroxide will be used as an exemplary chemical to compare exposure limits, but the exposure limits for other chemicals are usually in the same sources, though some jurisdictions list carcinogens separately.

The Canadian provinces each set their own occupational exposure limits, though the majority of them follow the American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit values (TLVs). The occupational exposure limits for each Canadian province (P) and Territory (T) is set out below:

• Federal Government: follows ACGIH
• Alberta (P): Based on 2006 ACGIH, exposure values tabulated.
• British Columbia (P): largely follows ACGIH, but issues its own table of exposure values. H2O2 = 1 ppm 8 Hr TWA..
• Manitoba (P): follows ACGIH
• New Brunswick (P): follows 1997 ACGIH
• Newfoundland and Labrador (P): follows ACGIH
• Northwest Territories (T): follows ACGIH, legislation pending
• Nova Scotia (P): follows 1976 ACGIH
• Nunavut (T)follows ACGIH, legislation pending
• Ontario (P): Published list or else ACGIH, H2O2 is under ACGIH
• Prince Edward Island (P): follows ACGIH
• Quebec (P): 1 ppm 8 hr TWA
• Saskatchewan (P): 1 ppm 8 Hr TWA, 2 ppm 15 min TWA (STEL)
• Yukon (T): 1 ppm 8 hr TWA, 2 ppm 15 min TWA (STEL)

Note: Regulations are always subject to change and to the readers should verify that the above information is correct before relying on this information. 

The current ACGIH TLV for hydrogen peroxide is 1 ppm calculated as an 8 hour TWA.  The ACGIH TLVs are time weighted exposures (TWA) that are reviewed periodically based on the available scientific data.

For the US, the OSHA PEL for hydrogen peroxide is 1 ppm (8 hr TWA) with no short term exposure limit. Hawaii and Washington have the same 8 hr PEL, but also have a STEL of 3 ppm (15 min. TWA). 


There are significant jurisdictional differences between the US and Canada. In the United States, the Occupational Safety and Health Administration (OSHA) establishes safety standards for the entire country including permissible exposure limits (PELs) for workplace exposure to chemicals. Most state agencies with responsibility for workplace safety follow the federal limits, though a few, such as California, Washington and Hawaii set their own PELs but these state PELs are either the same or more restrictive than the OSHA PELs because of the Supremacy clause in Article VI of the US constitution.

Unlike the United States which has a strong federal government and relatively weak states, in Canada the opposite is true. In Canada there are ten provinces and three territories. The provinces are considered co-sovereign states with the federal government; and the territories though under the egis of the federal government, also promulgate their own laws. Thus people working with chemicals in Canada need to look at the requirements of each province and territory separately.