Unacceptable risks for the VIAP may pose both immediate threats to safety (e.g., fire or explosion potential from petroleum vapors or methane) and possible short-term adverse health effects (acute) from inhalation of toxic chemicals. While rare, the potential for these to occur is often the greatest after a new release but should be initially evaluated in the investigative process for structures within the lateral inclusion zone (LIZ).
NOTE: If strong petroleum odors are detected or combustible, explosive, or O2-deficient conditions are found to exist inside a building, then first responders should be contacted immediately.
The following scenarios are site conditions when short term or acute health effects are possible and need to be evaluated:
- NAPL is less than 5 feet from a structure,
- Soil vapor above the time-sensitive interim action screening levels (TS MSSLs),
- Petroleum odors have been identified within a structure, or
- NAPL has entered an underground conduit that can transport vapor directly to a structure.
Additional Information is provided in Attachment A.4 on the acute vapor risks associated with petroleum.