Consequence Modeling

Consequence modeling involves the determination of the impacts of process accidents involving hazardous materials on people, the environment, and the process.

The amount and form of hazardous material released is determined for toxic materials, flammables, and explosives (called the source term). The dispersion of the released material through and beyond the facility is studied. The distance traveled and area covered are determined. For toxic materials, their effects on people and the environment are evaluated. For flammables, the impact of the heat radiation from a fire on people and equipment is calculated. For explosive materials, the impact of blast overpressures on people, equipment and structures are calculated. Models tailored to each particular situation are used to evaluate consequences. Gas, two-phase, and liquid releases are modeled and their discharge rates are calculated. Dispersion is modeled for buoyant or heavy gases, as appropriate, taking account of the range of atmospheric conditions possible at the time of release. Toxicity data and dose-response models are used to model toxic effects. Various types of fires are modeled including pool, jet, flash, fireball, and warehouse fires. Types of explosions modeled include confined, unconfined, and dust explosions as well as BLEVEs (Boiling Liquid Expanding Vapor Explosion), thermal decompositions, and runaway reactions.

Details

Source term determination

We calculate the amount of hazardous material released in an accident and we provide a report that documents the results of the calculations.

Dispersion analysis

We calculate distances to various concentration endpoints for a released material and the area covered by the plume. We provide a report that documents the results of the calculations.

Consequence modeling

We determine the impacts of toxic material releases on people on-site and off-site and the environment and the impacts of fires and explosions on people and property. We provide a report that documents the results of the calculations.

Sensitivity, importance and uncertainty analysis

We determine the input variables to which the results of consequence modeling are most sensitive and we determine which variables play the most important role in contributing to the results of the analysis. We also propagate uncertainties in the input variables through the analyses to determine the uncertainties in the calculated results. We provide a report that documents the calculations.

Other Information

Companies employ dispersion and consequence modeling for various purposes including determining impact distances for EPA’s Risk Management Program (RMP) regulation, assessing the significance of hazard scenarios identified during PHA, and providing input to risk analysis. Reliance on purely qualitative analysis is insufficient where high consequence, low probability accidents are concerned since qualitative consequence estimates are subjective. Quantitative analysis provides a sounder basis for decision-making when considering the tolerability of catastrophic accident consequences.