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.

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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.

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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™.

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Two-Phase Flow Onset and Disengagement Methods

Two-phase flow is often considered in system hydraulics as well as the evaluation and design of pressure relief and effluent handling systems. A variety of scenarios can lead to two-phase flow under relief conditions.

In general, two-phase flow during relief can occur because of flow hydrodynamics and poor vapor/ liquid disengagement where (a) the liquid swells due to generation of vapor bubbles in the liquid 1, (b) fluid expansion occurs due to heating, and/or (c) the superficial vapor velocity is high enough through the pressure relief device. Oversized relief devices can induce two-phase flow because a large relief flow area yields a higher superficial vapor velocity. Runaway chemical reactions and/or chemical systems that are viscous and/or foamy almost always lead to homogeneous two-phase flow.

Two-phase flow can also occur by entrainment, for example, where gas is sparged at a high enough rate in the liquid. In some systems, condensation leading to two-phase flow in the discharge piping can also occur due to expansion cooling caused by pressure reduction through a control valve or a pressure relief device.

Numerous two-phase flow models have appeared in the literature. These models represent broad ranges of theory. Some are based on single-phase critical flow, others on homogeneous equilibrium flow, frozen flow, separated flow, slip flow, and/or non-equilibrium flow.

Homogeneous equilibrium flow models assume equal vapor and liquid velocities and calculate the change of quality with pressure using an isenthalpic or isentropic thermodynamic path. Homogeneous frozen models assume equal vapor and liquid flow velocities and that the quality is frozen along the flow path, i.e., no change with respect to pressure or temperature. The separated flow models assume different vapor and liquid flow velocities and account for mass, momentum and heat transfer between the separate phases.

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...

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.

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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.

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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 PRV 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...

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