top of page
Petrochemical plant with lights

RISK ANALYSIS

What is quantitative risk analysis (QRA)?

QRA is a methodology for performing facility siting that goes beyond a consequence assessment by including the likelihood that each release will occur and produce a hazardous outcome.  It is listed in API 752/753/756 as a valid method for performing a facility siting study and it must take into consideration numerical values for both the consequences and the frequencies of explosion, fire, and toxic material release scenarios. 

​

QRAs will provide the risk to both groups of people in the building (aggregate risk) as well as the individual. Both are typically presented as the risk of lethality and should be compared to company criteria for acceptable quantitative risk. 

​

The benefits of a QRA study are a more detailed picture of the hazards from all portions of the process for each hazard type. Since the frequency or likelihood of each scenario is included in the risk calculation, high-consequence but low-likelihood scenarios do not have as much weight in the results as compared to a consequence-only study. Also, being able to rank the scenarios and hazards as well as the buildings by risk enables better prioritization of remediation efforts. The downsides of a QRA are the complexity, cost, and duration.

QRA Steps

  1. Gather process documents including PFDs and PI&IDs with heat and material balance. Unit plot plans with equipment numbers are also needed.

  2. ​Segment the PFDs/P&IDs such that each highlighted segment has similar process conditions. Each segment will represent a release scenario using multiple leak sizes.

  3. Do a parts count of each segment which when combined with a historical leak frequency database will yield the release frequency for that scenario. We use the IOGP 434-01 Risk Assessment Data Directory - Process Release Frequencies and the Shell Shepherd method.

  4. Create individual hazard events for each scenario by considering weather cases, wind direction, ignition probability, and other probability modifiers.

  5. Survey and analyze occupied buildings for blast response and document individual and group occupancy

  6. Survey process unit congestion and other site features that impact hazard prediction

  7. Model explosion, fire, and toxic hazards for each scenario at each leak size. 

  8. Determine building occupant vulnerability for each hazard prediction

  9. Sum the individual and aggregate risk for each building and compare to company criteria

  10. Document the study in a technical report

  11. Provide risk mitigation options based on the  results and prioritization of buildings and hazards

FN risk curves

Get the benefits of QRA in your study

We have over 15 years of experience performing QRA for both large refineries and small gas plants and everything in between. Our knowledge of the methodology allowed our experts to write a fully featured QRA software tool to automate the millions of calculations needed to capture the full risk picture. This experience and deep fundamental knowledge of the process allows us to provide accurate risk results and insightful interpretation of the risk which help clients make informed decisions that minimize their risk most cost-effectively. 

Experience

Engineer Working on Desktop Computer, Screen Showing CAD Software with Technical Blueprint

  • Over 15 years of experience performing QRA's in the process industries

  • We have performed QRA for large refineries with 50+ units and smaller sites with only one unit

  • Our experts have developed QRA software that integrates with PHAST and enables us to do QRA's with hundreds of scenarios and buildings​

Results

Risk results, contours, and FN curves

  • A detailed technical report that defines inputs, explains calculation methods, provides calculation results, and summarizes them in a meaningful way

  • Results as a user-modifiable spreadsheet where you can:​​

    • Change building occupancy and see the risk changes​

    • Inspect which scenarios are providing the most risk using pivot charts and tables

    • Add mitigation factors to modify hazard results and see real-time risk updates on the impact 

  • Follow-up calls with our experts to make sure you understand the results and have a clear path forward on what mitigation options are best suited to your site
     

bottom of page