D. Receptors

Of critical importance to any risk assessment is an evaluation of the types and quantities of receptors that may be exposed to a hazard from the pipeline. For these purposes, the term receptor refers to any creature, structure, land area, etc., that could receive damage from a pipeline rupture. The intent is to capture relative vulnerabilities of various receptors, as part of the consequence assessment.

Possible pipeline rupture impacts on the surrounding environmental and population receptors are highly location specific due to the potential for ignition and/or vapor cloud explosion. Variables include the migration of the spill or leak, the sensitivity of the receptor, the nature of the thermal event, the amount of shelter and barriers, and the time of exposure.

Because gaseous product release from a pipeline is a temporary excursion, the pollution potential beyond immediate toxicity or flammability is not specifically addressed here for releases into the air. This discounts the accumulative damage that can be done by many small releases of atmosphere-damaging substances (such as possible ozone damages from green house gases). Such chronic hazards are considered in the assignment of the equivalent reportable release quantity (RQ _equivalent) for volatile hydrocarbons.

Ideally, a damage threshold would lead to a hazard area estimation that would lead to a characterization of receptor vulnerability with in that hazard area. Damage threshold levels for thermal radiation and overpressure effects are discussed in Chapter 14.