Mobile Monitoring Comparison Values

The purpose of the instantaneous baseline-derived investigation level (iBDIL) is to identify the presence of an abnormally high concentration of any monitored chemical in the ambient air, so that a follow-up source investigation and actions to decrease emissions can be carried out if necessary.

Key points about iBDILs:

• Instrument- and chemical-specific.
• Set at 10-times higher than the chemical baseline, with the instrument- and chemical-specific baseline determined by evaluation of mobile monitoring surveys.
• Not based on levels at which the chemical could cause health effects, because a chemical with a low toxicity that is being measured at levels much higher than are typical indicates a release that may require action (even if the measured concentrations don’t indicate a concern for human health).

The purpose of an instantaneous health-protective investigation level (iHPIL) is to indicate that an evaluation of the potential for chemical toxicity is warranted. An exceedance of an iHPIL could prompt stationary monitoring for 30 minutes to 1 hour, or collection of a 30-minute canister sample, as determined to be appropriate by TCEQ field staff. The resulting average concentrations can be evaluated for the potential to cause toxicity using a comparison value of an appropriate longer duration (e.g., 1-hour air monitoring comparison value (AMCV) or ^EMHBAL_1hr).

Key points about iHPILs:

• Health-protectively set equal to a 1-hour acute health-based comparison value such as a TCEQ 1-hour AMCV.
• Instantaneous chemical concentrations below the iHPIL will not cause health effects, but risks from concentrations above the iHPIL cannot be directly judged, therefore triggering further toxicity evaluation.

The purpose of the instantaneous health-based action levels (iHBALs) is to indicate when more rapid or greater action of TCEQ field staff may be required. An exceedance of an iHBAL could prompt stationary monitoring as well as increased vigilance for potential exceedance of an exposure mitigation value.

Key points about iHBALs:

• Set equal to 3-times a 1-hour acute health-based comparison value such as a TCEQ 1-hour AMCV.
• If an instantaneous concentration exceeds the iHBAL, then an exceedance of a longer-duration, health-based screening level such as the 1-hour acute health-based comparison value may also occur.

The purpose of the exposure mitigation health-based action levels (^EMHBALs) is to indicate that an evaluation of staff safety may be needed (i.e., staff may choose to take steps to decrease their potential for exposure in the field); as well as an evaluation of the need to communicate information to regional managers and/or incident command (as deemed applicable by TCEQ field staff). ^EMHBALs were derived for three durations: 5-10-minute average (^EMHBAL_10min), 1-hour average (^EMHBAL_1hr), or instantaneous concentrations (^EMHBAL_1sec). The ^EMHBAL_1sec is the primary exposure mitigation value that will be used by TCEQ field staff when data cannot be averaged in real-time in the field.

 The ^EMHBALs are set at levels well below those that would cause health effects.

Key points about ^EMHBALs:

• The ^EMHBAL_10min is set based on the lesser of: 3-times the 1-hr acute health-based comparison value, one-half an appropriate 15-minute occupational short-term exposure limit if available, or one-half an appropriate occupational ceiling value.
  • Only used when field staff have the ability to average data in real-time while monitoring.
• The ^EMHBAL_1hr is set at 2-times the 1-hr acute health-based comparison value.
  • Only used when field staff have the ability to average data in real-time while monitoring.
• The ^EMHBAL_1sec is set at 6-times the 1-hr acute health-based comparison value.