PT Notes
Part 1 - Are you Addressing Functional Resonance in Process Safety?
PT Notes is a series of topical technical notes on process safety provided periodically by Primatech for your benefit. Please feel free to provide feedback.
The concept of functional resonance recognizes that in complex systems, such as process plants, unexpected outcomes can emerge as a result of normal variations in different process functions interacting in unanticipated ways. Understanding such resonances can be used to predict potential process failures.
A simple example is provided by a polymerization reactor in which, on a particular day, the catalyst is more active than usual, for example, due to a fresher batch or a change in its composition. This increased activity results in a faster polymerization rate, which generates heat more quickly. Simultaneously, the cooling system is not operating at its peak efficiency, for example, due to scaling in the cooling pipes, reducing its capacity to remove heat. Under these conditions, even though each individual variability might be considered manageable, their simultaneous occurrence could lead to the reactor temperature exceeding safe operating limits and a possible runaway.
This interaction between variabilities in process functions has a compound effect that may not be anticipated by examining each source of variability in isolation. It is called a functional resonance. The simultaneous occurrence and interaction of multiple variabilities in process functions, rather than a single "root cause", can lead to unforeseen and possibly catastrophic outcomes.
Process safety accidents have occurred because of functional resonances. Here are some examples of classic accidents. The contributors to these accidents have been simplified for the purposes of this PT Note.
Deepwater Horizon Oil Spill (2010)
Variability 1: A negative pressure test, which was intended to ensure the integrity of the well, was misinterpreted, leading the crew to believe it was successful when it was not.
Variability 2: At the same time, the blowout preventer, a device intended to shut off the well in case of an unexpected surge of oil and gas, malfunctioned.
Functional resonance: The combination of the misinterpreted test and the malfunctioning blowout preventer led to a catastrophic failure, an explosion, loss of eleven lives, and a massive oil spill in the Gulf of Mexico.
Piper Alpha Oil Platform (1988)
Variability 1: Maintenance work led to a pressure safety valve being removed and temporarily replaced with a blind flange.
Variability 2: Simultaneously, a shift change and miscommunication meant that the next crew was unaware of this change, and they attempted to restart a compressor.
Functional Resonance: This led to a gas leak, which ignited and resulted in a series of explosions and a massive fire on the platform, causing numerous fatalities.
Chernobyl Nuclear Power Plant (1986)
Variability 1: A late-night safety test was being conducted to simulate a power outage and determine how long turbines would spin and supply power to the main circulating pumps.
Variability 2: During this test, power unexpectedly dropped to an almost zero level. The attempt to increase the power, and certain reactor design flaws, led to an uncontrollable power surge.
Functional Resonance: The simultaneous occurrence of these variabilities, combined with human decisions and reactor design issues, led to a steam explosion, subsequent reactor meltdown, and the release of large amounts of radioactive materials.
Space Shuttle Challenger (1986)
Variability 1: Cold weather caused the rubber O-rings, which were intended to seal the joints of the solid rocket boosters, to become less flexible.
Variability 2: Design flaws existed in the O-ring seal system.
Functional Resonance: The cold weather and the design flaws combined resulting in the O-rings failing to seal one of the joints, allowing pressurized hot gas to reach outside, leading to a catastrophic explosion of the shuttle shortly after liftoff.
Bhopal Gas Release (1984)
Variability 1: Water entered a storage tank containing ethyl isocyanate (MIC).
Variability 2: The safety systems designed to neutralize any accidental MIC leaks were inadequate or not functional at the time.
Functional Resonance: The reaction between water and MIC resulted in a massive release of toxic gas, causing thousands of deaths and significant long-term health impacts for many more people.
In all these accidents, multiple variabilities or factors aligned, leading to significant disasters. The concept of functional resonance provides a means to understand such complex interactions and their cascading effects in complex systems, such as modern process plants.
Part 2 of this PT Note describes a framework for applying the concept of functional resonance in the process industries.
If you would like further information, please click here.
To comment on this PT Note, click here.
You may be interested in:
