RENEE MONTAGNE, HOST:
From time to time this summer we'll be taking a few minutes to talk about the science behind summer activities in a series we're calling Summer Science. And we've enlisted the help of NPR's science correspondent Joe Palca. Today we'll hear about Joe's trip to a picnic area with a fire pit. There, with the help of Dan Madrzykowski from the National Institute of Standards and Technology, Joe explored the science of building a campfire.
JOE PALCA, BYLINE: So, what do you need? I mean, we have some stuff here. But what are the basics? Tell us what we need to make a good fire.
DAN MADRZYKOWSKI: Well, to make any kind of fire of all, you have to refer to the fire triangle. There are three legs to a triangle. You need fuel, you need some source of heat, and you need oxygen. And where do you get that? Well, we have oxygen in the air around us. For fuel we've got all kinds of dry wood lying around here. And then that source of heat would be matches or a lighter to get it started.
PALCA: Now, to start, you want to get some light stuff that's easy to burn. That's the tinder. Something like dried pine needles or leaves.
MADRZYKOWSKI: And then you want to get some thinner twigs. What we're looking at here from an engineering perspective is a good surface-to-mass ratio.
PALCA: OK. Surface-to-mass ratio - complicated term. But all it basically means is material with a good surface-to-mass ratio for starting a fire is something that's got a lot of surface but not a lot of weight, like a piece of paper. Logs, on the other hand, have a lot of weight compared to their surface - they're bad for starting a fire. Logs, bad. A piece of paper or dry leaves?
MADRZYKOWSKI: That's perfect for igniting.
PALCA: So you've got a handful of leaves there. Is that a right amount or, I mean, can you start with less than that, more than that?
MADRZYKOWSKI: Oh, a handful or two should give us a good start if we can find some good dry kindling wood.
PALCA: OK. Well, let's put those onto the grate and then we'll go look for kindling.
(SOUNDBITE OF TWIGS CRACKING)
PALCA: I found one. Woo-hoo.
MADRZYKOWSKI: We've got a couple of handfuls of material. And now we could head back to our fire pit.
PALCA: So we've got a pretty good collection of twigs and small sticks here and we're sort of making, like, a nest almost.
MADRZYKOWSKI: You don't want to build it too tight. You want to make sure it can get plenty of air and oxygen in there to mix.
PALCA: Remember that triangle. We've got fuel, we've got plenty of oxygen, now all we need is our heat source.
MADRZYKOWSKI: Who's got the matches?
MADRZYKOWSKI: Very good, very good.
(SOUNDBITE OF LIGHTING MATCH)
PALCA: In a few minutes, we've got a blazing fire. So science helped us get the fire going, but it can also help us put it out.
MADRZYKOWSKI: The nice thing about thinking about fire as a triangle, if you break any leg of that fire triangle, you can put the fire out. You can stop the combustion. So if we take the oxygen away by covering this fire with sand, we could suppress the fire. If we take the heat away by applying water to it, we break that leg of the fire triangle and we can suppress the fire. Or if we just let it run out of fuel or take the fuel away from it, we break that leg of the fire triangle.
PALCA: Fire off and we're done.
(SOUNDBITE OF AD)
UNIDENTIFIED MAN: Only you can prevent wild fires.
PALCA: Joe Palca, NPR News.
(SOUNDBITE OF MUSIC)
MONTAGNE: And at NPR.org you'll find step-by-step instructions for building your own fire. Print them out and burn after reading.
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MONTAGNE: This is NPR News.
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