As Lieutenant Gordon Ambelas tore through the burning Brooklyn high-rise in search of victims last July, he fought back not only smoke and flames, but junk.

The apartment's resident had stashed piles of trophies, luggage, and other trinkets around his home. “You could walk in, but you couldn't turn," one neighbor said. Within minutes, Ambelas was carried out unconscious and badly burned. Within hours, he was dead.

That’s far from the only time hoarding has made a house fire much more dangerous. Earlier this month an Ohio firefighter was hurt in a fire where hoarding was so severe that firefighters couldn't enter part of the house. This week, two people died in a Queens, New York, house described as having “hoarding conditions.”

Last week, firefighters from 14 different parts of New Hampshire were called to a single fire. The cause of the blaze might never be known, the local fire chief said, because layers of pet feces and other waste coated the floor.

Earlier this week I attended a fire-fighting gathering in Maryland. It was only a simulation, but I got a sense of how difficult it must be to fight a live fire. It’s fairly typical for firefighters to encounter dense smoke, but occasionally they must also work in total darkness. They feel along walls with their thick gloves for signs of human life. If they stay inside a burning structure for too long, they risk running out of air. The maze-like conditions created by stacks of newspapers or Christmas ornaments make every step of this process harder.

Hoarding is a psychological ailment that was once considered to be similar to obsessive-compulsive disorder, but is now a distinct diagnosis. Among the condition’s many devastating mental and physical consequences is that it can make the sufferer more likely to die in a fire. Clutter can block exits and trip residents when they try to escape. Boxes and papers act like kindling, making a fire rage more intensely.

Studies suggest about 2 to 5 percent of people hoard, but the firefighters I spoke with said they see “hoarding conditions” in about 25 percent of homes they enter. It’s not clear whether hoarding is becoming more widespread, but some cities say they are seeing an uptick. If firefighters and city officials are sensing a rise, it might be because hoarding is more common among the elderly, and the U.S. population is rapidly aging.

It might also be a symptom of modern life. “We find it more common today because people have more possessions,” New York Assistant Chief Jim Hodgens told the AP. “People have two, three TVs. People have more clothes today. I think as a society we have more stuff. … It complicates the search.”

The issue has become so prevalent that firefighters have a special name for a suspected hoarding house: “Collyer’s Mansion,” after the 1940s case of two brothers who were found dead in their Harlem brownstone amid hundreds of tons of musical instruments, books, and tapestries.

Some fire officials are joining “Hoarding Task Forces” in their cities to try to clean up hoarders’ homes preemptively. They’re also training to battle hoarder fires specifically.

“If you suspect that hoarding is present, call the second alarm—NOW!” one such tip sheet reads. “The workload that your firefighters will experience is greatly increased due to the sheer amount of stuff you’ll need to work around or through.”