DIERS Technology for Two Phase Relief System Design

In industries where two-phase fluids, such as liquid-gas/vapor mixtures, are present, it is crucial to have robust relief systems in place to protect overpressure scenarios that can lead to equipment failure and potentially catastrophic incidents. Traditional relief system design methods often fail to properly account for the unique complexities associated with two-phase relief, especially for uncontrolled runaway reaction scenarios.

To address this challenge, the Design Institute for Emergency Relief Systems (DIERS) has developed advanced technologies and methodologies specifically tailored for two-phase relief scenarios.

Understanding Runaway Reactions: Runaway reactions pose a significant threat in chemical processes as they can rapidly increase in temperature and pressure beyond the capacity of process equipment. The resulting pressure can exceed design limits and potentially lead to catastrophic incidents, as demonstrated in the 2007 incident at T2 Laboratories in Jacksonville, Florida, as reported by the US Chemical Safety and Hazard Investigation Board (CSB). It is crucial to comprehend the behavior and potential failure scenarios of these reactions in order to develop effective emergency relief systems that can successfully mitigate and control the situation.

DIERS Technology and its Application: DIERS technology provides a systematic and scientific approach to the design of two-phase emergency relief systems. This methodology involves a combination of experimental data, mathematical modeling, and engineering expertise. Embracing the DIERS technology involves adopting state-of-the-art tools and methodologies to analyze and design comprehensive two-phase relief systems. DIERS technology focuses on the fundamental understanding of underlying runaway reaction kinetics and physical phenomena such as liquid flashing, two-phase flow, and hydraulic phenomena that occur during emergencies. By accurately simulating these scenarios, DIERS technology enables engineers to devise effective and reliable relief systems tailored to the specific process conditions of the plant.

Compliance with Industry Standards: Adhering to industry standards and regulations is crucial when implementing an emergency relief system. The Occupational Safety and Health Administration (OSHA), in its 1992 Process Safety Management (PSM) regulation (CFR 1910.119), recognizes DIERS technology as “Recognized and generally accepted good engineering practice” (RAGAGEP). OSHA also recommends “re-evaluating the size and capacity of the emergency relief system using the methodology of the American Institute of Chemical Engineers (AIChE) DIERS technology” when a relief device is involved in a runaway reaction venting incident.

Furthermore, DIERS technology takes into account international standards established by the American Society of Mechanical Engineers (ASME) and the American Petroleum Institute (API 520 and API 521). Incorporating these standards into the design process ensures compliance and promotes a safer operating environment.

Procedures for Two-Phase Relief System Design using DIERS Technology

  1. Critical Parameters and Scenario Analysis: DIERS technology prioritizes the identification of key parameters that play a role in runaway reactions. Through the analysis of factors such as the type of reaction system (vapor, gassy, or hybrid), reaction kinetics, heat generation rate, vessel geometry, and environmental conditions, a well-designed emergency relief system can be developed. Conducting scenario analysis based on plausible failure scenarios assists in determining the appropriate design parameters for pressure relief devices.
  2. Identification of Two-Phase Relief: The first step in utilizing DIERS technology is to identify potential two-phase relief within the process or equipment being analyzed. This involves assessing the possible conditions that may lead to two-phase flow, such as vaporization of liquid in vessels, flashing due to pressure drop in pipes, or natural evaporation in heat exchangers. By identifying these conditions, engineers can focus their analysis on areas more likely to require two-phase relief.
  3. Two-Phase Hydraulic Modeling: DIERS technology employs drift-flux hydraulic modeling tools to simulate the behavior of two-phase fluids (homogeneous flow, bubbly flow, or churn turbulent flow) during relief events. This involves capturing key parameters such as fluid properties, flow rates, liquid swelling, pressure drops, and temperature profiles. The developed models are able to predict the flow regimes and behavior of the two-phase fluids, allowing engineers to optimize the relief system design and validate its performance against specified criteria.
  4. Relief Load Calculations: The next step involves performing relief load calculations to determine the magnitude of the potential relief event. Using DIERS technology, engineers can calculate the mass, volume, and flow rates of the two-phase mixture to be relieved during different relief scenarios. These calculations help determine the required relief device size and capacity, ensuring that the system can handle the specified relief loads effectively.
  5. Relief Device Sizing and Selection: Proper sizing and selection of relief devices are vital components of an emergency relief system for runaway reactions. DIERS technology assists in correctly sizing pressure relief valves, rupture discs, or other relief devices based on the process conditions and required relief rates. This ensures that the emergency relief system can handle the maximum potential pressure and flow rates, thereby protecting process equipment and personnel.
  6. System Integration and Validation: Once the relief devices are selected, the two-phase relief system needs to be integrated into the overall plant design. This involves incorporating necessary isolation valves, vent headers, and other components to create a comprehensive relief network. DIERS technology provides guidance in properly integrating the system, validating its performance, and ensuring that it meets the required safety standards and regulatory requirements.

Why use DIERS Technology?

Industries that deal with liquid-gas two-phase mixtures, such as petrochemical, pharmaceutical, and chemical plants, face specific challenges in designing effective emergency relief systems. Failing to address these challenges adequately can have serious consequences, including equipment damage, environmental pollution, and harm to personnel. This is where the implementation of DIERS (Design Institute for Emergency Relief Systems) technology becomes crucial.

DIERS technology provides a unique solution by predicting when two-phase flow will occur and determining the extent of vapor-liquid swell. It is important to note that two-phase flow, which is very common in these industries, requires a larger relief area than either vapor or subcooled (non-flashing) liquid flow. Therefore, implementing DIERS technology for two-phase relief design is essential for industries dealing with liquid-gas mixtures and other two-phase scenarios.

Why use Prime Process Safety Center?

  1. Expertise: We have extensive experience and expertise in implementing DIERS technology for two-phase emergency relief systems.
  2. Compliance: By using DIERS technology, we ensure compliance with industry standards and regulations, such as those set by OSHA, ASME, and API.
  3. Safety: DIERS technology is recognized as a “Recognized and generally accepted good engineering practice” by OSHA, promoting a safer operating environment.
  4. Accuracy: DIERS methodology provides a reliable methodology for re-evaluating the size and capacity of the emergency relief system, especially in cases of runaway reaction venting incidents.
  5. International standards: DIERS technology accounts for various international standards, facilitating global compliance and compatibility.
  6. Assurance: Choosing us for utilizing DIERS technology ensures that your two-phase emergency relief system is designed and implemented using proven, industry-accepted practices.


1. What is DIERS technology and how does it relate to runaway reactions?

DIERS (Design Institute for Emergency Relief Systems) technology is a methodology used for the design, analysis, and evaluation of emergency relief systems in various industries. It is commonly used to design relief systems for managing runaway reactions, ensuring safety in process industries.

2. What is a runaway reaction and why is it a concern?

A runaway reaction refers to a situation where a chemical reaction becomes uncontrollable and generates excessive heat or pressure, which can lead to equipment damage, hazardous releases, and potential safety risks to personnel and the environment.

3. How can DIERS technology help with the design of relief systems for runaway reactions?

DIERS technology provides a systematic approach to analyze and evaluate the reaction kinetics, thermal data, and process conditions to accurately design emergency relief systems that can effectively handle and manage runaway reactions.

4. Can DIERS technology be used to prevent runaway reactions?

While DIERS technology primarily focuses on the design of emergency relief systems, it can indirectly help in preventing runaway reactions by providing insights into reaction kinetics, process parameters, and potential deviations that can trigger a runaway reaction.

5. Are there specific guidelines or standards associated with using DIERS technology for runaway reactions?

Yes, the AIChE’s (American Institute of Chemical Engineers) Center for Chemical Process Safety has developed guidelines and recommended practices for using DIERS technology to design relief systems for runaway reactions, such as the Guidelines for Pressure Relief and Effluent Handling Systems.

6. Is specialized training required to implement DIERS technology for runaway reactions?

A thorough understanding of chemical process engineering and reaction kinetics is beneficial for implementing DIERS technology for runaway reactions. Additional training or guidance from experts in the field is recommended to ensure accurate and effective use of the technology.

7. Can DIERS technology be applied to all types of runaway reactions?

Yes, DIERS technology can be applied to various types of runaway reactions, including exothermic reactions, polymerization reactions, and reactive distillation processes, among others. However, it is important to note that the specific characteristics and complexities of the reaction will influence the design of the relief system.

8. Are there any case studies or examples showcasing the successful implementation of DIERS technology for runaway reactions?

Yes, there are many case studies and examples available that highlight the successful application of DIERS technology for designing relief systems for runaway reactions. These case studies can provide valuable insights into best practices and industry-specific considerations.

9. Can DIERS technology help with the evaluation and optimization of existing relief systems for runaway reactions?

Yes, DIERS technology can be used to evaluate and optimize existing relief systems for runaway reactions. By conducting a thorough analysis and utilizing advanced modeling techniques, potential deficiencies in the existing system can be identified, and necessary modifications or upgrades can be recommended.

10. How can I get started with utilizing DIERS technology for designing relief systems for runaway reactions?

To get started, it is recommended to consult with experts who are experienced in using DIERS technology for runaway reactions. They can provide guidance, conduct process evaluations, and assist with the design and implementation of robust relief systems to manage runaway reactions effectively.