Definition:
Dispersion analysis is an analytical method used to estimate how a released hazardous material—such as a gas, vapor, or aerosol—spreads through the environment over time. It evaluates the concentration, direction, and extent of a release under defined conditions and is commonly applied to accidental releases from process equipment, including pressure relief valves, vents, flanges, or loss-of-containment events.
Dispersion analysis is not a functional safety activity in itself, but it provides critical consequence information that feeds into several parts of the functional safety lifecycle and broader process safety work.
Key Points:
- Dispersion results are frequently used to support hazard and risk assessments (H&RA) by defining credible consequence distances and affected areas.
- Dispersion analysis evaluates the consequences of a release, not the likelihood.
- Common sources analyzed include pressure relief valves, vents, piping failures, and vessel releases.
- Results depend on release rate, material properties, meteorology, and geometry.
- It is a core input into qualitative risk analysis.
- Outputs may feed into hazardous area classification.
Example:
A pressure relief valve discharging a flammable gas is evaluated using dispersion analysis to determine the downwind concentration profile under worst-case conditions. The resulting impact distances are used to support hazardous area classification and to inform the consequence severity assumed in a risk assessment.
Cited Source:
- Discussion from May Kay O’Conner Process Safety Center: https://psc.tamu.edu/research/consequence-analysis/