Why ammonium nitrate explodes

Maggie Koerth-Baker is going to be on MPR’s Daily Circuit tomorrow to talk about last evening’s tragic explosion of a fertilizer plant in Texas.

But — spoiler alert — in her Boing Boing column today, she gets to the nuts and bolts about ammonium nitrate fertilizer.


In fact, since the 1950s, ammonium nitrate-based explosives have basically supplanted the older dynamite explosives used in mining and other industries, precisely because they are so much safer and harder to detonate. Ammonium nitrate isn’t even classed as an explosive, Oxley said.

“It’s very difficult to get it to detonate at a reasonable scale,” she said. “You can toss 50 pounds of it in the back of your car and it will do nothing. With something like dynamite even a gram or two is highly explosive.”

But, obviously, ammonium nitrate does explode sometimes. So what makes those circumstances different?

The most important factor is how much ammonium nitrate you have. Fifty pounds ain’t nothing. But a couple hundred tons of the stuff is a different story. If that huge amount of ammonium nitrate also catches on fire … then you have a problem.

It’s a great column, which you can find here.

Coincidentally, the worst industrial accident in U.S. history occurred in Texas City, Texas 66 years ago Wednesday. It involved ammonium nitrate.

  • Jim G

    We know this product will explode under the right circumstances. So why would anyone locate a middle school, high school, nursing home, and apartment complex near a fertilizer plant that could explode? Don’t they have zoning regulations in Texas? Maybe that’s just a blue state thing.