Determining PAC Values

AEGLs, ERPGs, and TEELs all serve the same general purpose—to assist those who are responsible for planning for and responding to chemical emergencies. For any particular chemical, PAC values are generally determined from AEGL, ERPG, and TEEL values based on the following hierarchy:

• use AEGLs (including final or interim values) if they are available
• if AEGLs are not available, use ERPGs
• if neither AEGLs or ERPGs are available (as is the case for the vast majority of chemicals in the PAC data set), use TEELs.

In those relatively few cases where there is a departure from this hierarchy, the reason for this digression is is noted in a comment field in the PAC data set.

The PAC data set provides four different PAC benchmark values for each chemical (i.e., PAC-0, -1, -2, and -3). Starting with “0”, each successive benchmark is associated with an increasingly severe effect that involves a higher level of exposure. The four benchmarks present threshold levels for:

0 - no adverse health effects
1 - mild, transient health effects
2 - irreversible or other serious health effects that could impair ability to take protective action
3 - life-threatening health effects

Only TEELs have a “0” level value, therefore the PAC-0 value is always the TEEL-0 value. A more detailed definition of the individual AEGL, ERPG, and TEEL benchmarks that are used to define PACs is presented by SCAPA.