What Have We Learned from the Pemex LPG Explosion in Mexico City?

In this episode, Trish and Traci discuss the 1984 Mexico City LPG disaster in Mexico, where a pipe burst at a Pemex facility. This led to a massive explosion equivalent to five Hiroshima bombs. A combination of factors, including poor management of change, inadequate fireproofing and proximity to residential areas, resulted in 500 deaths. Key lessons included the importance of proper land use planning, risk assessment and fire protection.

Transcript

In today's episode we're going to be looking back 40 years to Nov. 19, 1984 and what is known as one of the deadliest industrial disasters in world history. The incident took place at a storage and distribution terminal for liquefied petroleum gas belonging to the state-owned oil company, Pemex. Can you give us a little bit of a brief overview of what happened that day?

What Happened in Mexico City in 1984?

Trish: The refinery was about 400 kilometers or about 250 miles away, I guess, from the terminal where LPG was being pumped into. And during that pumping activity, a pipe burst in the line that was transporting the LPG and that caused a substantial loss of containment of LPG. And the LPG continued to flow for five to 10 minutes under pressure ensuring that it became a very big vapor cloud at that point in time. And then it found an ignition source in a waste flare pit and ignited and exploded, and it was a massive explosion that occurred.

It's estimated to be something around in excess of 300 terajoules, which is about five times the size of the Hiroshima atomic bomb to put it in perspective. A massive, massive detonation that occurred and then the subsequent fire that took place after that. This facility had a couple of spheres of LPG in storage as well as 48 other cylindrical vessels. And so the ensuing fire then resulted in further explosions as those spheres suffered catastrophic failure in what we call a boiling liquid expanding vapor explosion, which again is another very violent sort of explosion that occurs. Tragically, it's estimated that this incident killed somewhere between five and 600 people when it occurred, making it at that time the world's deadliest incident from a process safety perspective, as you mentioned.

Lessons Learned from the Pemex LPG Explosion

Traci: The imagery there is just profound. What were some of the key lessons learned from this disaster in terms of process safety improvements?

Trish: So there were some issues around some changes that had been made to the facility, and so the perennial issue of management of change comes up again. Changes were made and certain parts of equipment were changed out at a lesser pressure rating. So, potentially there was an over-pressure situation here. Failing to adequately assess and make adequate risk-based and engineering-based changes to our systems can lead to these issues.

Aside from the first explosion, though, something else that then occurred was those fears of LPG that I mentioned. Their legs weren't adequately fireproof, so as the fire continued to burn, the legs actually gave way. Steel could only take a certain amount of thermal energy before it actually starts to lose its strength and bend and fail. And so not only were there explosions, but the spheres actually collapsed off their legs as well. And all of these things just made a tragic and horrific incident even worse at every step of the way. There were issues around how any firefighting was able to be conducted because there were impacts to the equipment as well. All up, it was one of these instances where issue after issue after issue kept compounding and making this worse. But fundamentally it came back to management of change, operating discipline, and the engineering of the facilities to start with.

Traci: Now you talk about some of those complications. What about the layout and design of the plant? How did they contribute to the severity of the accident?

Trish: It was quite congested and effectively that had an impact in not only the spread of the vapor cloud and then obviously the subsequent detonation that came from it, but also in the emergency response to it as well, making it really difficult to respond to because of just the congestion in the area.

Cost of Inadequate Safety Systems

Traci: You mentioned the safety systems, the inadequate safety systems in place, such as the gas detection system and the emergency isolation capabilities. Can we talk a little bit about how that played in the escalation of this accident?

Trish: Without having adequate systems in place like gas detection, they were unable to adequately determine what was going on. And then potentially in a gas release you have a short window of time to prevent an ignition taking place. You do that typically by using a water fog, so your spray monitors in a fog formation to actually knock the cloud down, prevent it spreading. But without adequate detection you can't then respond adequately in a fast enough way. So they were unable to respond adequately in that particular way.

And so that did cause or it contributed to the ongoing issues associated with it. From the emergency isolation perspective, there was obviously a gap with being unable to then adequately isolate once that pipe actually ruptured. So as I said, five to 10 minutes of gas flowing out of a pipe under pressure without actually being able to isolate it at any close points to prevent a significant release of gas at that point in time. When you've got a pipeline under pressure and you end up with a hole in it, the pipeline pressure has to relieve somewhere. It's going to go out the hole unless you can isolate and hold that pressure back in some other way. So because they were unable to adequately isolate both at the spheres but also at the pipeline inlet from a remote perspective, that then led to a lot more gas being released than should have been, had we been able to have seen that isolated earlier.

Boiling Liquid Expanding Vapor Explosion

Traci: How did this lead to greater awareness of the risks associated with BLEVEs and the need for proper risk assessment and land use planning?

Trish: This facility was based very close to a small town, and so it resulted in so much more significant damage because of the proximity to the local community. So this saw an enormous impact on the residents of the town. And in fact, many of them killed in this incident when it took place. The land use planning aspect, this really highlighted that we need to take a step back and fully understand the ramifications when we have such a significant hazard sitting so close to a population source like we saw here. So that's one point. It really highlighted the tragic consequences we can see when an industrial incident goes outside of the fence line and starts to impact to the community. It also had various other aspects of learning associated with it because we did then start to look a lot more at how we respond and understanding BLEVEs even further.

So, we understood the mechanism of BLEVE, but I don't think we'd really seen it on this sort of scale before. And it's led to I think a lot more focus in certain industries on things like fireproofing of pressure vessels so that we can't BLEVE them. If they have a fireproof coating in them, then the thermal energy from the fire can't boil off the liquid inside and therefore result in the subsequent BLEVE. We saw a big change in how we did things, including things like fireproofing the legs of equipment. Now, we still have a lot of facilities out there that don't have fireproofing on them though, and should there be a significant fire in these facilities, we will see structural failures of supporting members and columns as they suffer weakening under the thermal energy. But it's not as easy as it sounds because you may think, well, why don't we just fireproof everything?

Once we fireproof it, we then lose the ability to see what's happening to the steel underneath the fireproofing. And if we have a slight crack in the fireproofing, we start to get potentially water ingress and we then start to get corrosion, but we can't see it because it's all hidden. So it's not as simple as let's just cover everything up. We actually still need to then understand and monitor the corrosion and corrosion under that fireproofing, which is similar to the phenomena of corrosion under insulation.

Again, water ingress into the insulated material starts to corrode the steel pipeline or vessel inside. We can't see it. We see a weakening and a subsequent failure. So we need to make sure that we really understand how we are managing our risks and how we're taking these high hazards and managing them to a tolerable risk level. And that includes putting in the preventative measures that we have and the passive control measures, the passive barriers, things like fireproofing, but also making sure we then adequately control corrosion management to ensure we don't have a corrosion event occurring that we don't know about that is one day going to cause a significant incident for us.

Why Do We Make the Same Process Safety Mistakes?

Traci: Interesting points there and things that sometimes aren't thought of. So thank you for bringing those up. Our podcast is never here to point fingers. We're here to learn from past incidents to help avoid future events. It's what I say in every episode. So when I ask this next question, I want you to keep that in mind that I'm not pointing fingers, I'm just asking the question. Pemex has had its share of safety incidents since this tragedy. The most recent was a chemical leak at the Pemex Deer Park Texas Refinery on October 10th of this year that killed two contract workers and resulted in dozens of injuries. Are they not learning from mistakes or just making new ones? And when I say that, I'm not, again pointing fingers, I'm just trying to get my arms around how these types of things keep happening.

Trish: Yeah, I understand the premise of your question. It's important to note that sadly, Pemex are not alone in this. We could rattle off a number of different companies that have seen a number of incidents occur over many, many decades. It comes back to, in my opinion, I think an issue of organizations failing to learn. Now, the great Trevor Kletz once said, "Organizations have no memory. Only people have memory, and when they move on, the accidents reoccur." And so it's not about apportioning blame to companies or individuals. In fact, it's actually about thinking about how we actually ensure that we can take the lessons that we see on a regular basis because there are no new lessons. We do just keep seeing repeated types of events again and again and truly create that learning in the organization. Because I'm not sure that we've really yet figured out how to create a learning organization anywhere because it always does come down to the individuals.

And as individuals move on, they take with them their experience and we bring in newer people that don't have the same experience. And so this is why we need to make sure we have excellent knowledge management systems in organizations where the history is kept, that we have documented basis of safety for the design of our facilities. We understand why designs were made in a certain way, what the meaning of it was, what the purpose of it was, so that when we do a management of change, again, a structured process, that we can adequately consider what the current hazard is and what change that hazard occurs, if any, when I make this change I'm proposing and then make sure we document it and then make sure we train people in it and then make sure all of our systems are updated to account for it as well.

So it's a very broad question. It's not about any one company, it's about how humans learn and the fact that we can have an experience, but that actually doesn't mean we've learned. It means we've had an experience. Until we take the time to go back and reflect on that experience, we'll never truly realize the learning from it. And so making sure that we do reflect as individuals, as companies. And making sure that we document adequately everything that has occurred, how it's occurred, that we thoroughly investigate, that we do put in place corrective actions to prevent reoccurrence, and that we also understand why things work when they work. This is not just about why things don't work. We can actually also learn a lot from why things do work and how can we improve what we do.

We need to continuously improve as well. So it's not a clear-cut answer. I think to a certain extent as humans, we have some fallibility that we need to understand so that we can adequately manage them. We can't get rid of them. We are human and actually being human and being fallible makes us unique and it actually makes us very special creatures because we do have the ability to learn from these things, but we need to make sure that as organizations, we help them learn through that whole ecosystem that we're part of.

Traci: Trish, is there anything you want to add to this topic?

Trish: I mentioned earlier that 500 to 600 people were killed in this incident, and at the time it was the world's worst incident that we've ever seen. 1984 was an incredibly tragic year for process safety globally. And so I'd encourage people to go and take a look at this incident because it actually got overshadowed very shortly after it happened. We'll talk about that next month. But do take a look at this incident, take a look at some of the lessons from it, and think about how you can take those into your organization, have that organizational reflection, and create a true learning so that you never see anything like this happen in your organization.

Traci: Well, Trish, as always, you help us reflect and learn and document to continuously improve. And we appreciate your time with us. Unfortunate events happen all over the world, and we will be here to discuss and learn from them. Subscribe to this free podcast so you can stay on top of best practices. You can also visit us at chemicalprocessing.com for more tools and resources aimed at helping you run efficient and safe facilities. On behalf of Trish, I'm Traci, and this is Process Safety with Trish and Traci. Thanks, Trish.

Trish: Stay safe.