What are the key factors to consider when estimating flammable release frequencies?

1 Data sources

The first factor to consider is the data source you use to estimate flammable release frequencies. There are different types of data sources, such as historical data, generic data, and expert judgment. Each one has its advantages and limitations, and you need to choose the most appropriate one for your situation. Historical data are based on actual events that occurred in similar facilities or processes, and can provide realistic and specific estimates. However, they may not be available, representative, or complete. Generic data are based on statistical analysis of large datasets from various industries and regions, and can provide consistent and comprehensive estimates. However, they may not reflect the specific conditions, design, or operation of your facility or process. Expert judgment is based on the knowledge and experience of qualified professionals, and can provide flexible and customized estimates. However, it may be subjective, biased, or inconsistent.

2 Release scenarios

The second factor to consider is the release scenarios you include in your estimation. A release scenario is a combination of the release source, location, size, rate, duration, and direction. You need to identify and select the most relevant and credible release scenarios for your facility or process, based on the hazards, equipment, piping, layout, and operation. You also need to consider the possible failure modes, causes, and mechanisms that could lead to a release, such as corrosion, erosion, fatigue, impact, vibration, overpressure, or human error. You should use a systematic and structured approach, such as hazard identification (HAZID), hazard and operability study (HAZOP), or failure modes and effects analysis (FMEA), to identify and select the release scenarios.

3 Release models

The third factor to consider is the release models you use to estimate the release size, rate, and duration. A release model is a mathematical or physical representation of the fluid flow and thermodynamics of a release, based on the fluid properties, pressure, temperature, and geometry. You need to choose the most suitable release model for your release scenario, based on the fluid phase, state, and composition, and the release type, shape, and orientation. You also need to consider the uncertainties and assumptions involved in the release model, and how they affect the accuracy and reliability of your estimate. You should use a validated and verified release model, such as those available in software tools or standards.

4 Release frequency

The fourth factor to consider is the release frequency you assign to each release scenario. The release frequency is the expected number of times a release scenario occurs per year, based on the data source and the release probability. You need to calculate or estimate the release frequency for each release scenario, based on the data source you selected, and the failure frequency, exposure time, demand rate, and conditional probability. You also need to consider the uncertainties and variations involved in the release frequency, and how they affect the confidence and sensitivity of your estimate. You should use a consistent and transparent method to calculate or estimate the release frequency, such as those available in software tools or standards.

5 Release direction

The fifth factor to consider is the release direction you assume for each release scenario. The release direction is the angle or vector of the release jet or plume relative to the horizontal plane, based on the release location, orientation, and momentum. You need to assume or estimate the release direction for each release scenario, based on the release model you used, and the wind speed, direction, and turbulence. You also need to consider the uncertainties and variations involved in the release direction, and how they affect the dispersion and impact of your release. You should use a realistic and conservative assumption or estimate for the release direction, such as those available in software tools or standards.

6 Release mitigation

The sixth factor to consider is the release mitigation you apply to each release scenario. The release mitigation is the reduction or elimination of the release size, rate, duration, or frequency, based on the detection, isolation, depressurization, or suppression systems. You need to apply or estimate the release mitigation for each release scenario, based on the design, performance, reliability, and availability of your mitigation systems. You also need to consider the uncertainties and dependencies involved in the release mitigation, and how they affect the effectiveness and efficiency of your mitigation. You should use a realistic and conservative application or estimate for the release mitigation, such as those available in software tools or standards.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?