DIERS is an acronym which stands for the Design Institute for Emergency Relief Systems. It all started in an AIChE meeting in St. Louis, MO, in 1976. Three visionary savants like James Huff (from Dow), Walt Howard, and William Boyle (from Monsanto) took off from the meeting, went into an adjacent room, and brainstormed the idea of forming a process safety group to handle two-phase flow, runaway reactions and a computer program to do the job. First a name DIRE was proposed to signify that the consequence of not following the recommendation could be DIRE! Finally, the name DIERS was accepted as a technical entity within AIChE in 1976. Fauske Associates (FAI), Inc. developed the program named SAFIRE (System Analysis for Integrated Relief Evaluation – a FORTRAN-77 based program) in 1984. Dr. Art Shaw of Monsanto was impressed by a paper presented by Dr. Georges Melhem of Arthur D. Little, Inc, (ADL) in an AIChE meeting, and invited him to present a similar paper in DIERS Meeting. Dr. Georges Melhem of Aurther D Little (ADL), Inc. accepted the invitation, and presented a technical paper for the first time in 1991 in DIERS meeting impressing all attendees.
A consortium of 29 companies was formally formed by the name DIERS in 1976.
In 1995, ADL received a contract from AIChE to develop a computer program SuperChems(TM) for DIERS. SuperChems is an eclectic condensation of Computer Science, Mathematics, and Chemical Engineering, and is the product of a brilliant mind: Dr. Georges Melhem! Dilip Das bought SuperChems software for Bayer CropScience at Kansas City in 1997.
In subsequent years from 2007 through 2020, Dilip Das nominated Dr. Joseph Leung, Dr. Georges Melhem, Mr. Robert D’Alessandro, Mr. Peter Howell, and Dr. Marc Levin to Fellow of AIChE.
Dilip Das became the first Chair, SuperChems Technical Steering Committee, and brought a lot of improvements recommended by the users.
Dr. James Huff, one of the founding fathers of DIERS, established a methodology of determining the KD value of Pressure Relief Valves and KR values of Rupture discs experimentally. The method is described in ASME PTC-25.
There are some pillars which support this technology. As a pressure safety specialist or a recipient of process safety work, you should be familiar with these pillars. They are enumerated below.
1)The ERS design is not just a design issue; it is an optimization issue. In other words, the optimum ERS design is the one that brings the total cost of ERS design, effluent handling design and the environmental cost with the company risk at the minimum and the company potential at the maximum.
2) The term “two-phase homogeneous” is used in DIERS. It is an oxymoronic term because two phases cannot be homogeneous. A phase is a physically distinct, mechanically separable, homogeneous portion of matter. Its real use lies in the simplicity of determining the physical properties of a system.
3) The Coupling Equation and its solution
This equation is one of the main pillars of DIERS technology and is mathematically complex. The simplified description of how the equation is developed is as follows. When a tank containing a liquid is exposed to fire at the bottom and sides, the vapor nucleation starts at the bottom and sides. Liquid swells and reaches the vent provided by the relief device. The Coupling Equation simply balances the net vapor flow in the vapor generation with a trial and error of assumed vent size. Thus:
Vapor in the vent = vapor escaped from the swelled liquid + vapor trapped in the swelled liquid.
They are explained below:
VAPOR IN VENT = X0AVG
VAPOR ESCAPED FROM LIQUID = J/g∞ Rg,sACR
VAPOR TRAPPED IN SWELLED LIQUID = Xm(AVG – J/g∞ Rg,sACR)
Where:
X0 = flowing vapor quality in the vent
AV = vent cross section
G = vent mass flux
J/g∞ = Superficial vapor velocity at the liquid surface required to swell the liquid just to the top of the vessel.
Rg,s = vapor density at the relief pressure and corresponding saturation temperature
ACR = vessel cross-sectional area
The type of flow, such as Churn-Turbulent, Bubbly, Two-phase is determined by calculating the Psi parameter ( J/g∞ / U infinity). The U infinity is calculated from an empirical correlation that requires physical properties of the fluid such as the surface tension, liquid density, and vapor density.
From the calculated Psi parameter and known average void fraction in the vessel, and the fluid characteristics such as Churn-Turbulent, Bubbly, or homogeneous, the onset two-phase flow is determined. This complexity is avoided by the use of smart software such as the SuperChems.
As of January, 2026, Dr. Georges Melhem, CEO of ioMosaic, became the Chair of DIERS as Mr. Harold Fisher, stepped down from the Chair of DIERS and will work as Acting Vice-Chair. More changes are expected in the management committee. Two DIERS meetings are held each year.
Many unsung heroes like Marc Levin, Dan Smith, John Hauser, Passa Piland, and a few others continue work behind the scenes selflessly to improve the DIERS technology.
Finally, a new book Emergency Pressure Relief System Design, with 11 chapters and 14 appendices authored by DILIP DAS is published by AIChE/WILEY. This is an essential book for anyone, irrespective of experience, for process safety management.
To know more about this page, please contact Dilip K. Das 1-816-400-3238, [email protected]