Emergency Relief System Design

Reducing costs and increasing accuracy in the design or revalidation of relief systems.

Effective Emergency Relief System (ERS) design helps companies meet risk-management goals, compliance requirements, and sound business practices. ioMosaic provides a total ERS solution with our comprehensive ERS design services, from reactivity testing for design basis determination to calculations for Z-axis deflection from dynamic loads.

Learn More

How We Can Help You

Our team has decades of experience performing PRFS analysis and design.

Our risk-based approach helps mitigate near-unventable scenarios to a tolerable level of risk.

Better evaluate hazards in your facility with an accurate process simulation.

Delivering properly designed pressure relief systems that save both money and time.

Have a Question on Emergency Relief System Design?

Contact Us


Featured Resources

RAGAGEP Considerations for Overtemperature Protection in Relief Systems

How to Calculate ETTF or ETTY in Fire Exposure Scenarios

Reasonable estimates of the expected time to failure (ettf) or expected time to yield (etty) are required and necessary for effective risk management as well as effective emergency and fire protection and response. Read this paper for a demonstration of calculating ettf or etty in fire exposure scenarios with Process Safety Office® SuperChems™.

Read the White Paper

Forget the Omega Method and Master VdP Integration Instead

Reliable flow estimates are essential for the sizing and selection of process equipment including but not limited to relief devices, process piping, and depressuring systems. In addition, reliable flow estimates from loss of containment scenarios can significantly influence the quality of consequence, risk analysis, and facility siting studies as well.

Existing methods for the calculation of flow rates range from those for simple, non-reacting, single phase, steady state flow to methods for dynamic, multiphase, reacting flows. Ideal nozzle flow calculation methods are heavily used in relief systems and risk analysis studies and are detailed in numerous standards and industry guidelines including the International Organization for Standardization (ISO), the American Society of Mechanical Engineers (ASME), the American Institute of Chemical Engineers (AIChE) Center for Chemical Process Safety (CCPS) and Design Institute for Emergency Relief Systems (DIERS), and the American Petroleum Institute (API).


Relief systems studies often include different types of flows such as non-equilibrium, subcooled, liquid, vapor, two phase, supercritical, and retrograde and phase change (RPC) flows. Flow estimates can be influenced by vapor quality, the presence of solids, slip, viscosity, chemical reactions, piping and fittings losses and geometry, chemical composition, temperature, pressure, etc. In addition to flow rates, reliable flow methods are expected to yield reliable estimates for reaction forces, location of choke points, sound power levels, exit temperatures and pressures, exit compositions and vapor quality, two phase flow regimes, etc.

We explore in this document the origins of ideal nozzle flow methods for single and multiphase flow including Δh, direct vdP integration ( vdP), simple reduced analytical models, and complex reduced analytical models. We also explore the advantages and disadvantages of those methods for simple and complex flow systems.

Several case studies with practical examples are included using Process Safety Office® SuperChems™ software.

The Thermodynamics of Nozzle Flow

The origin of all ideal nozzle flow methods can be traced back to the first law of thermodynamics or conservation of energy. Let’s consider a vessel containing a multiphase mixture that is exchanging mass and energy with its surroundings. If we define our thermodynamic system to include all the vessel contents, we can write the first law of thermodynamics as follows:


Our Team

Georges A. Melhem, Ph.D., FAIChE

President & CEO The founder of ioMosaic and internationally renowned expert in the areas of pressure relief and flare systems design, chemical reaction systems, process safety and risk analysis. Read more...

Neil Prophet

Senior Vice President and Partner He brings over 20 years of experience in pressure relief and flare systems design project management and engineering expertise for chemical, pharmaceutical and petrochemical companies. Read more...

John Barker, Ph.D.

Director The head of our international offices in the U.K. and the Kingdom of Bahrain and an expert in risk management for oil, gas and transportation. Read more...

Marcel Amorós Martí

Director and Partner His expertise consists of a diverse range of industries from chemical and petrochemical to oil and gas and utilities. Read more...

Charles Lea, P.E.

Director, Minneapolis Office Lead He directs a number of large technical projects across multiple offices and is also responsible for all project management in our Minneapolis office. Read more...

Matthew LeVere, P.E.

Senior Safety and Risk Management Consultant Experienced in PRFS design and analysis for clients in the petrochemical, chemical, and pharmaceutical industries. Read more...

Neal Dahlheimer, CPPM

Senior Safety and Risk Management Consultant Technical lead on PRFS projects for chemical, petrochemical and oil facilities as well as QA/QC reviews and training on advanced techniques for complex systems. Read more...

James Close

Safety and Risk Management Analyst Mr. Close is focused on pressure relief and flare system design and analysis for large chemical and petrochemical companies in Europe and the United States. Read more...

Featured Videos


Emergency Relief System Design Workflow

This PSE module performs efficient tracking of process safety related data and analysis. A customized workflow allows for a specific operating unit or the entire facility to be studied and evaluated for compliance.

Download the Flyer

Featured Case Studies

Validate Relief System Performance and Flare System Capacity for Increased Unit Charge Rate

A major petroleum company recently increased production capacity and required an analysis of its existing relief systems to validate performance and design. As a result of increasing production capacity and debottlenecking studies, several refinery units were found to be operating at charge rates higher than the design basis for the relief systems documentation.

View Case Study
A refinery approached ioMosaic for the purposes of ensuring that pressure relief capacity was adequate for the loss of liquid seal scenario in a high-pressure separator (2,000 psig). They were also concerned about the pressure waves that would occur in the high-pressure separator’s outlet lines on rapid closing of the isolation valves and sought our expertise.
A large oil refinery with a very complex flare network had become so complex that the tools the refinery was using to evaluate the flows through the flare network could not adequately model the system. Management no longer had confidence that their model results reflected the actual network performance and therefore, could not be sure the system would perform properly in the event of a global relief scenario at the facility.
A multinational energy company wanted to complete an evaluation of a pressure relief valve system in order to comply with the PSM standard OSHA 29 CFR 1910.119 which requires that employers compile information pertaining to the equipment in the process, including relief system design and design basis. 


Featured Services

Pressure Relief and Flare System Design

Our risk-based approach helps mitigate near-unventable scenarios to a tolerable level of risk and develop economical designs for more credible events. Read more...

Relief Header and Flare Analysis Systems

Delivering properly designed pressure relief systems for refineries and chemical plants that save both money and time. Read more...

Latest News

Want to Get the Latest News from ioMosaic?

Sign Up Now