Lessons Learned from a Recent Reactor Explosion

Basar Ozar + Jens Conzen

Learn key lessons on importance of reactor safety and overpressure protection after Tarragona chemical explosion.

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Earlier this month, a massive explosion at a petrochemicals facility in Spain killed three people and injured several others. The strong explosion and following fire occurred during the evening hours and was still burning 24 hours later. This tragic incident is being described as one of the most serious chemical reactor accidents in Europe in recent years and will have a tangible impact on the petrochemical production industry.

While investigations and root cause analysis are still ongoing, it appears that the ethylene oxide reactor catastrophically failed. Based on similar incidents we have researched and consulted on, inadequate cooling or the inadvertent heating of the reactor are possible root causes.

Exposing a reactor to excessive heat can lead to uncontrollable exothermic runaway reactions in which temperature and pressure will rapidly increase. This isn’t always catastrophic—an adequately sized, well maintained, and functioning emergency relief system can relieve the pressure and reduce this risk. But this is only the case if this scenario was considered in the technical basis of the design and incorporated into the system. That’s why we encourage periodic reviews of the design basis as processes are changed over time and we conduct periodic process hazard analyses (PHAs).

How Does Ethylene Oxide Behave?

Ethylene oxide (which is used to make antifreeze and pesticides) is normally handled under pressure as a liquid, but at ambient conditions it is a gas that is heavier than air. Its boiling temperature under atmospheric conditions is 10°C (50°F) and may polymerize exothermically, or join to form larger molecules, if heated or contaminated. If the polymerization takes place inside a container, the container may rupture violently. Ethylene oxide is very flammable and toxic—ignition sources near the failure location will most likely cause explosion of the vapor during the initial discharge.

To make matters worse, ethylene oxide vapor may continue to evaporate from the failed reactor vessel after the initial explosion causing health effects in the surrounding area. An atmospheric dispersion analysis can address which areas should be avoided for personnel exposure and which areas have an imminent explosion risk. Understanding how far toxic and flammable gases travel allows chemical production facilities to adequately prepare for evacuation and emergency response in a worst-case scenario.

Other Considerations in Chemical Explosions

In the Spanish chemical plant explosion, a one-ton metal sheet killed a man almost two miles away from the plant while he was sleeping in his bed. In a chemical explosion, projectiles can potentially travel long distances. This tragedy emphasizes the amount of energy stored in pressurized vessels, the importance of emergency planning and the consideration of explosions affecting communities which are miles away.

Time will tell what caused this event. It is important that the lessons learned will be publicly communicated, so that the industry can learn from it to prevent similar accidents in the future. A key lesson is already apparent: the release of flammable and toxic gases and the trajectory of fragments should be considered in emergency planning.

OSHA's process safety management (PSM) standard contains requirements for the management of the processes using highly hazardous chemicals to help assure safe and healthful workplaces. A crucial part of the PSM program is a thorough investigation of incidents to identify the chain of events and causes so that corrective measures can be developed and implemented. Reach out to our process safety team to learn more.

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