This week, multiple outlets shared a story that played on people’s worst fears: in Russia, 28-year-old Ekaterina Fedyaeva was accidentally “embalmed alive” during an operation. But what does this mean exactly, and how is it possible?

Fedyaeva was undergoing a surgery to remove ovarian cysts. But doctors accidentally gave her formalin, which is a fluid with a very high proportion of formaldehyde, the chemical used to preserve dead bodies. (Reports differ on how this happened. Some outlets said that she was given an IV drip, but local reports suggest that a nurse simply “washed the surgical site” with formalin instead of saline.) The details are grisly: Fedyaeva complained that she was dying as her organs failed, according to The Washington Post. Her mother said she lived with the solution for 14 hours after the surgery and has called the hospital error “murder.”

Formalin is 40 percent formaldehyde, says Caleb Wilde, author of Confessions of a Funeral Director and a sixth-generation funeral director in Pennsylvania. It’s stronger than anything embalmers use. “If she had a bag, and if the entire IV bag was injected into her system — well, I just don’t know how she lived for 14 hours,” he says. “I have never been around formalin, and I don’t even know how caustic that is.” (He notes that this particular hospital seemed to have formalin on hand to sanitize their surgical instruments.)

The Verge spoke to Wilder about the process of embalming, his skepticism over the details of the Russian case and the history and future of the technique.

This interview has been lightly edited for clarity.

What exactly is “embalming”? Most people think of it as the “preservation of dead bodies,” but is that an accurate definition? And how long does embalming last?

I think funeral directors would say that the primary purpose of embalming is restoration, and the secondary purpose is preservation. You want to have the body look presentable for viewing at the funeral, but you’re not looking to create a specimen that can be viewed 50 years from now in some anatomical facility. So, preservation is the second order of importance.

That said, if the body is buried in a dry place, I think you could dig up a lot of embalmed bodies and — as long as they were embalmed well — they are still going to be recognizable 50, 60, 70 years later. Of course, there are a lot of other factors at play. If there’s any water that’s gotten into the vault or the basket, the decomposition is going to exponentially increase.

Roughly speaking, what are the steps of embalming?

The basic idea is that you inject the arterial system with embalming fluid. We tend to use the right carotid artery [a major artery on the side of the neck]. You make an incision, and you inject it with embalming fluid. The injection pushes out the blood and pushes in the embalming fluid, distributing it throughout the body via the arteries.

Then, there are parts of the body that aren’t reached through the arterial system, and that’s the abdominal area. So we inject the abdominal area with a trocar, which is like a large syringe. We stick it into the body and pump very strong embalming body into the abdomen directly, and that’s how it gets into the part that’s not reached by the arteries.

So you don’t need to remove organs?

No, we’re not removing organs. The fluid we use in the trocar is very strong and, for the most part, is able to preserve the entire abdomen and chest.

The chemical formaldehyde is used to preserve bodies. What does it do exactly?

Formaldehyde changes the tissue on a molecular level so that the bacteria can’t feed on the tissue. You could say it tears apart the constructs of your tissue. The embalming fluid that we use is a conglomeration of a bunch of different things. It has the formaldehyde, but it also has some disinfectants, so not only does it render the tissue unable to be fed on by bacteria, it also kills the bacteria itself.

What about formalin, the solution given to the Russian patient? What’s the difference between that and formaldehyde?

Formalin is formaldehyde dissolved in water. Formalin is 40 percent formaldehyde, so it’s stronger than anything funeral directors use.

For context, we use two types of fluid for embalming. One is arterial and one is for the cavities or the abdomen. The arterial fluid we use at our funeral home is about 30 percent formaldehyde, and we mix that in with water and that together creates the embalming fluid. At that point, it’s about 1.5 to 2 percent formaldehyde, which is already strong enough to restore and preserve the body.

The cavity fluid is about 20 percent formaldehyde. It’s incredibly strong-smelling. If a teaspoon gets spilled on the floor, that whole section of the funeral home will stink and cause a burning sensation. It’s not pleasant. It’s a chemical smell that you know you shouldn’t be breathing in. And that’s 20 percent. Formalin is double that. I have never been around formalin, and I don’t even know how caustic that is.

What are the implications here then, for the Russian patient?

If she had a bag, and if the entire IV bag was injected into her system — well, I just don’t know how she lived for 14 hours. So I’m thinking that maybe the entire bag was not injected into her system. But then again, it’s not like a gunshot wound where we have a bunch of examples and things we can reference to know what really happened. It’s obviously unethical to try to embalm someone alive, so we don’t have other examples.

The heart probably pumped the formation through the arterial system, and so it would have spread all throughout her body. I can only imagine that it would have felt like a burning sensation. You’re being ripped apart on a molecular level from the inside out.

You said that you don’t know how she could have lived for 14 hours. In general, how long does embalming take? And how do you know when the process is finished? What do you check for?

There’s a lot of relativity, but embalming can take anywhere from one to four hours.

As I mentioned before, the embalming fluid is a conglomeration of different things, and one of them is a coloring agent. So, the part of the skin that is receiving the embalming fluid changes color, and that’s how you know it’s working. You can make the skin darker or lighter or whatever you want. There’s a hardening effect as well. You can feel around the body and the parts that receive the fluid will be harder than the parts that didn’t.

Speaking of harsh chemicals, do embalmers worry about being exposed to them?

OSHA [Occupational Safety and Health Administration] has a hand to play in the way that prep rooms are designed in funeral homes. There has to be a certain amount of airflow, fans, and so on. Of course, no embalmer likes it when somebody spills some cavity fluid. For me, my nose starts to run and my throat feels like it’s burning, my eyes are watering. And that’s when I’m wearing my gown. You’ll report an incident in your own records if it’s serious, but it’s very rare.

People, understandably, fear being buried alive. On the other side, do you fear starting to embalm someone, only to find out that they’re still alive?

Yeah, that’s a legitimate fear for me. I’m always a little bit more observant when things start out because I just want to make sure, and so I’ll wait a minute after I make the first incision to make sure there are no signs of life.

When somebody dies at the hospital, it’s pretty much a 100 percent guarantee that they’re dead. You have heart monitors, oxygen monitors, and so on. But a lot of people are choosing to die at home under hospice care, and that changes things. I’ve never encountered a living body, and I don’t know any funeral director who has. But always, I worry in the back of my mind. That would be incredibly traumatic.

How common is embalming? What percentage of dead bodies are embalmed?

Embalming is a phenomenon is that is peculiar to the United States. In the United Kingdom, about 90 percent of people choose cremation, for example. And here, embalming is becoming less and less popular.

For our funeral home, about 40 percent of the people choose embalming. It varies, too, based on political persuasion. Generally, more conservative states tend to embalm while the more liberal ones tend to cremate. I actually take the minority view among funeral directors that it is not necessary for the majority of circumstances. You can put a body that’s unembalmed in a cooling container like a morgue fridge, and it’s generally going to look okay a couple days after death.

Why is embalming such an American phenomenon?

The United States has what I call “a grief bond.” It’s not a psychological term, it’s just something I’ve observed. Sometimes when things are exceptionally emotional, we kind of tend to bond the things irrationally. So, embalming for the US became incredibly popular during the Civil War and after the Civil War. And that is really the difference between us and the rest of the Western world. The Civil War created an impetus for embalming to become something that was quite popular. Without that, I don’t think we’d be any different than any of the other Western countries.

How the process of embalming changed a lot since then? Have there been a lot of technological advancements?

No. This is pretty much the way it’s always worked. It’s just the basic displacement of the arterial systems, so you’re injecting embalming fluid and removing blood. There have been different machines, but the idea is basically the same. We knew how to do this for a long time before it became acceptable as a social practice.

If embalming is becoming a lot less popular, what is becoming more popular?

The green burial, which is a rediscovery of ancient traditions, is what I want to see happen and what is starting to pick up. You give your body back to the land. Essentially, you just put it in the ground to allow the earth to take back your nutrients. It’s unembalmed, the casket is biodegradable, and it’s not put in a vault. I think a lot of people are resonating with that idea because it is a very green idea, and that’s becoming part of the popular consciousness of being environmentally friendly.

Update April 10th, 2018 4:30 p.m. EST: This post has been updated to show that reports conflict regarding how the patient was poisoned with formalin.