Wednesday, May 20, 2009

Water-filled dog bowl starts house fire?

You know it's possible to use ice to start a fire.

Here's a story of water starting a fire.

UPDATE 1: This space reserved for the first commenter with video showing that they used a bowl of water as a lens to start a fire. Get out there, Mythbusters! I will link to your video clip!

UPDATE 2: Our attempts with a large, hemispherical mixing bowl and black posterboard lead me to doubt the likelihood of this explanation. The dog bowl in the story is a frustrum of a right circular cone, so lensing effects don't seem plausible. One might retreat to a position that the rim of the bowl acted as a mirror. But reflections from a water-glass boundary? The intensity simply isn't there.

In my Mythbusting opinion, the "dog bowl as magnifying glass" explanation holds no water.


Anonymous said...

Sad but awesome.

Stevie (Tommy Chong) Ray said...

Reminds me of Golding's description of how Piggy's glasses were used to start a fire in The Lord of the Flies. Piggy was nearsighted (as I recall) and thus would need a DIVERGING lens. Maybe he meant to say they started a virtual fire?
If the water bowl in question was hemispherical, then I believe the rays from the sun would diverge upon leaving the water-bowl interface.
I think that if a bowl was the cause of that fire, it was due to somebody doing a bowl near the dog's water dish.

Dean Baird said...

I've ben able to use a hemispherical mixing bowl to "smoke" some black posterboard and dry leaves. Actual ignition was not observed.

The dog bowl doesn't seem to me to have any particular "optical qualities."

If I cut some glass into a disc, that doesn't make it a lens. The water-filled dog bowl is little more than a disc of refracting material.

But I eagerly await a nice confirmation video.

Anonymous said...

I know the person whose house was burned and last week we watched as the fire dept recreated the fire. the bowl was hemispherical.

Dean Baird said...

@Anon, I'm limited by my access to evidence. But
1. The dog bowl shown in the news piece was flat.
2. The wire rack shown in the piece has a flat "bed" on it. It appears it would support the bowl shown in the piece securely, but a hemispherical bowl would seem to tilt and shift.

A video of the fire department's recreation of the fire would be a valuable teaching tool. I promise to make a new post devoted to it should I ever get access to it. Please send a link.

The configuration shown in Keenan's reenactment would not work as a dog's water bowl. That bowl would be in pieces on the deck after three laps.

Don't get me wrong: I'm rooting for the object optics lesson--I'm a physics teacher! But I did have difficulty reproducing it with bright sunlight and black posterboard.

LeeTramp said...

Dean, the Seattle Times article cited by Anon shows the fire department using a curved bowl to test their hypothesis. The TV new report says "a dog dish like this." I suspect the TV crew grabbed the nearest glass bowl and used it as an example. I put my faith in the firefighters using a bowl that matched the bowl found at the scene. I vote that it's possible.