Quantitative Risk Analysis (QRA)

Quantitative Risk Analysis or QRA combines consequence modeling with event probability information to generate measures of risk.

Quantitative Risk Analysis (QRA) provides a numerical measure of risk. This allows an evaluation of risk imposed by a facility or operation to the public, onsite workers, or equipment by following a  rigorous risk anlaysis method. This analysis can also provide important insights into the risk profile that can be used to support process safety improvements. The study begins with the identification of potential hazardous events. The typical hazards considered include:

  • flammable vapor cloud
  • toxic vapor cloud
  • torch (jet) fire
  • pool fire
  • BLEVE fireball
  • vapor cloud explosion

With the above hazard types, failure case scenarios are selected to cover the potential impacts of concern. Each scenario is modeled using the CANARY software to produce a set of consequences that describe the potential hazards. Consequence modeling is performed for an extensive set of scenarios based on each failure case, which include:

  • Multiple accident outcomes (the various hazards)
  • Site-specific meteorological variations
  • Flammable fluid ignition (immediate, delayed, or none)
  • Vapor cloud explosion (dependent on a flammable cloud being ignited when within a confined or congested space)

For each variation of the failure case, a probability assessment is conducted. Beginning with the process equipment group that is associated with a failure case, the probability of each unique outcome is a product of:

  • Equipment failure rates (failures that result in a hazardous fluid release)
  • Conditional probabilities for flammable cloud ignition (immediate or delayed)
  • Conditional probability of weather parameters (wind speed, atmospheric stability, wind direction)
  • Conditional probabilities associated with equipment use or occupancy

Once the consequences and probabilities are defined, they can be combined into measures of risk. These measures of risk can account for endpoints specific to the population vulnerability and the population density and distribution. Quest can present the results of a QRA in a concise manner, using multiple presentation methods including:

  • Location-specific individual risk (risk contours, or LSIR)
  • Individual risk per annum (IRPA)
  • f-N curves (societal risk)
  • Other measures such as risk tables or PLL comparisons

The last step in a quantitative risk analysis is comparison of the results to a company’s risk criteria, or to acceptable risk criteria/guidelines published by governmental organizations. Quest Consultants provides a wide range of experience and expertise presenting these results in a regulatory setting to various agencies around the world. Our services are especially applicable to the petrochemical or oil and gas industry, chemicals industry, LNG facilities, pipeline industry, and transportation industry.