- [Professor Waldie, special guest star Bill Nye, the Science Guy, is looking at a tall taper candle lit before him on a desk, with Charlie and Larry watching on]
- Bill Waldie: A back draft is a fascinating phenomena. We can demonstrate it with this candle. It's also called a smoke explosion. The flame causes the hot gases rising from the candle to...
- [he blows out the candle, which promptly flickers back alight]
- Bill Waldie: reignite.
- Dr. Larry Fleinhardt: Somehow I missed the fact that the CalSci Engineering Department had a combustion lab.
- Bill Waldie: It's pretty neat, huh? We converted it from an old laundry room.
- Charlie Eppes: Well, thank you Professor Waldie, for setting this whole thing up.
- Bill Waldie: Bill, please. And you don't have to thank me. Creating the conditions for a back draft? It's just, way cool.
- [He walks them over to the miniature crime scene setup]
- Bill Waldie: Well, here's our booth. And, as noted in the arson report, we have: insulated compartment, combustible ceiling. Now, this geometry will starve the fire just enough, so that when this door is opened, oxygen will rush inside, creating a gravity current of cold air and hot gasses and, boom
- [he snaps his fingers]
- Bill Waldie: smoke explosion, aka, a back draft. All we need now is the heat source.
- Dr. Larry Fleinhardt: Ah, yeah, that would be me.
- [He pulls a pack of cigarettes from his jacket and pulls one out]
- Dr. Larry Fleinhardt: I thought we could use the same brand that the arson investigator found.
- [He wraps one cigarette in a new book of matches and hands it to Bill, who sets it in the booth]
- Dr. Larry Fleinhardt: And you're ready to go.
- Charlie Eppes: Where'd you get a cigarette?
- Dr. Larry Fleinhardt: [smirks] I know a guy.
- Charlie Eppes: Okay, so, Stevens said that the arsonist probably placed the ignitor near some fuel, like, like a seat cushion.
- Bill Waldie: Mm-hm.
- [He picks up a singed piece of cushion]
- Bill Waldie: This type of foam is an excellent hydrocarbon-based fuel.
- [He snaps a piece off and sets it in the booth with the cigarette and matches, then the three of them don protective eye glasses, and Bill strikes a match to light the tip of the cigarette]
- Bill Waldie: Okay.
- [Bill shuts the door, sealing the booth, and after a moment the cigarette ignites the book of matches, however the flame dies as fast as it ignited, leaving the foam untouched]
- Bill Waldie: [Charlie watches a temperature gauge creep up, starting at 300 degrees Fahrenheit, quickly jumping to 400 and climbing]
- Charlie Eppes: Temperature's rising.
- Bill Waldie: When the temperature inside reaches 600 degrees, we'll open the door and add oxygen.
- Charlie Eppes: Okay, well. If the scorch marks and flame indicators were recorded for a 5:41 AM start time
- [he glances behind him at some other gauges]
- Charlie Eppes: then wind and outside pressure are a check.
- Dr. Larry Fleinhardt: And at 600 degrees we should be good to go on a back draft.
- [Larry steps behind a protective, see-through curtain, and Charlie watches the temp gauge skip past 500 degrees on its way to 600 and ducks behind his own curtain]
- Charlie Eppes: We're almost there.
- [Bill extends a thin metal tool from behind his own curtain, using it to grasp the booth door as Larry mutters Easy, and Bill pops the door open with a hiss - but there's no explosion. They all come out from behind their curtains, puzzled]
- Bill Waldie: Huh. Did we ventilate the booth properly?
- Charlie Eppes: According to my calculations, yeah, we did.
- [He glances back at his chalkboard full of equations]
- Charlie Eppes: Heat release, burn rate, air, time.
- Dr. Larry Fleinhardt: There's no error in your math...
- [Charlie scoffs at him]
- Dr. Larry Fleinhardt: No, no, that's a statement, not a question.
- Charlie Eppes: [quietly, as realization dawns on him] The booth fire couldn't have been caused by a back draft.