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What is Relief System Design?

Posted by The Fauske Team on 05.02.17

"A relief system is an emergency system for discharging gas during abnormal conditions, by manual or controlled means or by an automatic pressure relief Emergency Relief System and Relief Valve Sizingvalve from a pressurized vessel or piping system, to the atmosphere to relieve pressures in excess of the maximum allowable working pressure (MAWP)." - Petrowiki

Fauske & Associates, LLC (FAI) was the principal research contractor for the Design Institute for Emergency Relief Systems (DIERS), an extensive R&D program sponsored by 29 companies under the auspices of AIChE and completed in 1985.  Company founder, Dr. Hans K. Fauske served as the principal investigator and overall leader of the DIERS research project.  A primary purpose of that effort was evaluation of emergency relief vent requirements, including energy and gas release rates for systems under upset conditions and the effect of two phase flow on the emergency discharge process.

The DIERS program resulted in the development of a bench scale low thermal inertia adiabatic calorimeter, which was first commercialized as the Vent Sizing Package (VSP). Later improvements led to the VSP2. The Reactive System Screening Tool (RSST TM) was introduced by FAI in 1989 to provide an easy, inexpensive approach to the DIERS testing method. Enhancements led to the Advanced RSST (ARSST) in 1999. FAI uses the DIERS-based VSP2 and ARSST calorimeters to characterize chemical systems and design emergency pressure relief systems. Both instruments provide vent sizing data that are directly applicable to the process scale.

Adiabatic calorimeter testing provides data for relief system design, safe scale-up of chemical processes, and changes to process recipes.  Safe process design requires knowledge of chemical reaction rates, character and energy release - all of which can be obtained from a low phi-factor adiabatic calorimeter such as the VSP2 (Vent Sizing Package 2) or ARSST (Advanced Reactive System Screening Tool).


Where Can I Learn More about Relief System Design and Vent Sizing?

Courses, handbooks and papers are available with a quick internet search. FAI provides courses, for example, either in our state-of-the-art lab setting or your location of choosing.  The next available course is: 

Relief System Design Course
May 15-16, 8 am to 4 pm, FAI Headquarters, 16w070 83rd Street, Burr Ridge (Chicago area), IL, CEUs: 1.6 (16 PDH)

Unlike other emergency vent sizing courses, this curriculum highlights simplified calculation methods capable of giving safe - but not overly conservative - relief system designs, with an emphasis on reactive chemistries and the role of two-phase flow.

Benchmarking of these methods will be illustrated with incidents and available plant data. Utilization of methods and equations will be demonstrated through practical design examples, covering vapor, gassy and hybrid systems.

Course Topics - Day 1

  • Introduction to Vent Sizing and Case Study
  • History of DIERS
  • Codes and Standards Explanation
  • Parameters Affecting Relief System Design/Fundamentals in Vent Sizing
  • Non-Reactive Fire Sizing
  • Vent Sizing Based on All Gas or Vapor Venting

Course Topics - Day 2

  • Discharge Coefficient Evaluation
  • Simplified Two-Phase Flow Methods for Vapor, Hybrid and Gassy Systems
  • Two-Phase Flow Through Relief System Design
  • Stable Relief Valve Sizing Operation
  • Containment and Disposal Considerations
Learning Outcomes
  • Understand up-to-date DIERS relief vent sizing methodologies and models, as well as the role of single and two-phase flow in venting behavior
  • Perform vent size calculations using the correct models and methodologies
  • Apply adiabatic calorimetry data
  • Be able to use hands-on techniques and “rules of thumb” to ensure that realistic vessel and vent size conditions are specified

For more information regarding relief valve sizing  and thermal hazards, contact  or, on the course, contact or call 630-323-8750. 

 Emergency Relief Vent Sizing for Fire Emergencies Involving Liquid-Filled Atmospheric Storage Vessels


Topics: vent sizing, Two phase flow, ARSST, VSP2, DIERS, scale up, relief system, two-phase, adiabatic calorimeter, safe scale up, reactive chemistry, vsp, vent size calculation


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