On June 8, 2022, the Freeport LNG export terminal in Texas experienced a serious incident: a vapor cloud explosion and fire that shut down operations for several months. This facility, responsible for a significant share of U.S. LNG exports to Europe, suffered the consequences of a blocked relief valve, a small oversight with a large-scale impact. The investigation traced the cause to a valve that was left closed after maintenance, resulting in a pressure build-up in a recirculation line. When containment was lost, flammable vapors escaped and ignited. Damage was limited thanks to swift emergency response, but the event serves as a strong reminder: in complex systems, human errors can cascade into crisis.
The strength of valve interlocks
This incident raises a key question: What could have prevented it? With valve interlocks in place, restarting the system would not have been possible unless the relief valve was confirmed to be open. Valve interlocks enforce the correct sequence of valve operations. The human oversight would have been caught before it became a hazard. Valve interlocks do not replace procedures; they reinforce them. They bring discipline to operations not by relying on memory or judgment, but by embedding safety into the physical process itself.
Valve interlocks guarantee over-pressure protection
In the process industry, pressure relief systems are often designed with built-in redundancy to allow maintenance on pressure relief valves (PRVs) without interrupting plant operations. However, to maintain full overpressure protection during the switchover between valves, additional safeguards are needed. A proven best practice is to use valve interlocks, which ensure that operators follow the correct sequence of steps, reducing the risk of error and maintaining system integrity throughout the process. Integrating valve interlocks on the inlet and outlet valves of a Pressure Safety Valve (PSV) system ensures that the correct sequence is always followed. Before a PSV is taken out of service for maintenance, the standby unit must be brought online. The interlocks also make it impossible to close the outlet valve unless the inlet valve has already been closed. This controlled sequence prevents dangerous scenarios like system overpressure, which can lead to equipment damage or serious safety risks.
Why human error is never just human error
It’s important to approach incidents like this with insight. The relief valve was left closed, but this was not an isolated lapse. The broader investigation pointed to insufficient follow-through on known issues, compromised expansion joints, and a lack of timely corrective action. When organizations rely solely on procedural compliance and informal knowledge, risk accumulates silently. Valve interlocks offer an effective countermeasure: they create a physical framework that supports human judgment with engineered certainty.
Elevating operational reliability
The Freeport LNG event highlights the risks of systems that count on human performance rather than built-in safeguards. As the industry continues to evolve and scale, the value of robust mechanical safeguards becomes clearer. Valve interlocks are not about distrust; they acknowledge that even the best teams can make mistakes. By ensuring that critical sequences cannot proceed unless safe conditions are met, valve interlocks elevate the standard of operational reliability.
From incident to insight
In the wake of the Freeport incident, the lesson is clear: where failure pathways exist, they must be closed, permanently and predictably. Valve interlocks provide a means to do exactly that. That is the promise and the power of valve interlocks.