Texas wildfire witnesses say they saw horses on fire. Are horses flammable?

Answers to your questions about the news.
April 12 2011 1:37 PM

Can a Horse Catch Fire?

Yes, with a little help.

Horses. Click image to expand.

Wildfires have burned more than 400 square miles in Texas since Saturday evening, and the editor of a weekly paper in Jeff Davis County told the Associated Press that he'd seen "horses on fire, buildings on fire, houses on fire." Wait, can a horse really catch fire?

Yes, under the right conditions. Like humans, a horse's body contains significant amounts of highly combustible fat. Yet, despite the fact that fat accounts for between 5 and 10 percent of a horse's body weight, you can't take a match to an appaloosa and expect it to catch fire. First of all, the skin acts as a barrier, insulating the horse's fat from the heat of the flame. Skin is difficult to ignite, and usually chars in the presence of heat. It takes up to 10 minutes of direct flame for skin to crack open and start leaking out rendered fat.

Even if a horse's body started to leak fat, it would be unlikely to go up in flames on its own. That's because animal fat is a lot like candle wax: It needs a wick to burn. (Fat and wax happen to have nearly identical heats of combustion. In fact, medieval candles were usually made of rendered fat.) You can't ignite candle wax without the aid of some other, porous material. The wick soaks up the wax at a steady rate and exposes it to the heat source. This parceling out of the fuel allows it to vaporize and burn.

A wick doesn't have to be a strip of cotton. It can be any substance that maintains a porous structure in the presence of massive heat. Just as the wick exposes the right amount of fuel to the heat, the fuel protects the wick from incinerating. (A candle wick wouldn't last very long without the wax.) In the case of a burning animal or human, the wick might be a carpet (PDF), a wool blanket, or a pile of leaves—anything that can soak up rendered fat and help the body burn.

That's not to say that, without a wick, animal flesh is flame retardant. There's a difference between charring—burning a substance by applying external heat—and ignition. As any crematorium demonstrates, exposing a body to a jet of flames for two or three hours will reduce it to ash. But if the flame is turned off at any time, the body will smolder, and the flames will quickly extinguish.


Nor is it impossible for a live animal to catch fire momentarily. Hair or fur can ignite, but they provide so little fuel that the fire would last only a few seconds—not long enough to compromise the integrity of the skin.

All of this helps explain why fire investigators usually find victims' bodies charred on the outside, but otherwise relatively intact. Even if flames managed to penetrate a victim's skin and start combusting his subcutaneous fat, his body probably wouldn't be incinerated. The flames would come up against several more layers of tissue that aren't likely to catch fire—like muscle and ligaments. A few cases of fully-cremated accident victims have given rise to the widely discredited mythology of spontaneous human combustion.

Got a question about today's news? Ask the Explainer.

Explainer thanks John D. DeHaan of Fire-Ex Forensics and author of Kirk's Fire Investigation.

Brian Palmer writes about science, medicine, and the environment for Slate and the Natural Resources Defense Council. Email him at explainerbrian@gmail.com. Follow him on Twitter.



Smash and Grab

Will competitive Senate contests in Kansas and South Dakota lead to more late-breaking races in future elections?

Stop Panicking. America Is Now in Very Good Shape to Respond to the Ebola Crisis.

The 2014 Kansas City Royals Show the Value of Building a Mediocre Baseball Team

The GOP Won’t Win Any Black Votes With Its New “Willie Horton” Ad

Sleater-Kinney Was Once America’s Best Rock Band

Can it be again?


Forget Oculus Rift

This $25 cardboard box turns your phone into an incredibly fun virtual reality experience.

One of Putin’s Favorite Oligarchs Wants to Start an Orthodox Christian Fox News

These Companies in Japan Are More Than 1,000 Years Old

Trending News Channel
Oct. 20 2014 6:17 PM Watch Flashes of Lightning Created in a Lab  
  News & Politics
Oct. 20 2014 8:14 PM You Should Be Optimistic About Ebola Don’t panic. Here are all the signs that the U.S. is containing the disease.
Oct. 20 2014 7:23 PM Chipotle’s Magical Burrito Empire Keeps Growing, Might Be Slowing
Oct. 20 2014 3:16 PM The Catholic Church Is Changing, and Celibate Gays Are Leading the Way
  Double X
The XX Factor
Oct. 20 2014 6:17 PM I Am 25. I Don't Work at Facebook. My Doctors Want Me to Freeze My Eggs.
  Slate Plus
Tv Club
Oct. 20 2014 7:15 AM The Slate Doctor Who Podcast: Episode 9 A spoiler-filled discussion of "Flatline."
Brow Beat
Oct. 20 2014 9:13 PM The Smart, Talented, and Utterly Hilarious Leslie Jones Is SNL’s Newest Cast Member
Oct. 21 2014 8:38 AM An Implanted Wearable Gadget Isn’t as Crazy as You’d Think Products like New Deal Design’s UnderSkin may be the future.
  Health & Science
Bad Astronomy
Oct. 21 2014 7:00 AM Watch the Moon Eat the Sun: The Partial Solar Eclipse on Thursday, Oct. 23
Sports Nut
Oct. 20 2014 5:09 PM Keepaway, on Three. Ready—Break! On his record-breaking touchdown pass, Peyton Manning couldn’t even leave the celebration to chance.