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You remember the time as a kid when you set an ant on fire. You positioned your dad’s magnifying glass a few inches above the ground, adjusting the angle ever so slightly until the spotlight of refracted rays rested precisely on your target.* Then you waited. 

It was innocent fun—except for some of us more sensitive folk—a sort of right-of-passage, backyard science experiment. But would you recall that lesson twenty years later while placing Fido’s clear glass water bowl on your deck? 

Investigators of a house fire in Bellevue, Wash., last week are suggesting an elevated 11-inch wide glass bowl of water magnified the sun’s rays onto a wood deck, sparking a blaze that caused more than $200,000 worth of damage.  Fortunately, nobody—including the two dogs—was injured.

To see if this dog bowl theory held water, Lt. Eric Keenan, the Bellevue Fire Department's community liaison officer, reconstructed the scene. He placed a partially-filled bowl on a wire stand nearly 14 inches above the sun deck at Bellevue City Hall. The atypical northwest spring conditions closely matched those on the day of the fire: a perfect “70 degrees and sunny, with light winds,” reported The Seattle Times. Sure enough, within about 15 seconds the small piece of cedar Keenan had set below the stand began to smoke under the sun’s concentrated rays. 
 
Thomas G. Brown, a professor of optics at the University of Rochester, agrees that the scenario is plausible, at least under very specific conditions. The bowl must be transparent—preferably glass—with an overall convex shape, according to Brown. A wider bowl would need to be set further from the flammable material to concentrate the sun’s rays. (The resulting energy, however, would be far greater than that created through a small bowl – or maybe even your dad’s magnifying glass.) The skies must also be clear, dry and the sun shining from more-or-less directly overhead.

“Of course, the Seattle area is a little like Rochester—it is a rare and wonderful day indeed when we get that kind of direct sunlight out of clear skies,” Brown tells ScientificAmerican.com. “But if it is going to happen, late spring is the time.”

*Note (6/3/09):  This sentence was changed after publication. As pointed out by one of our readers, the term "refracted" is more precise than "reflected" when referring to the sun's rays through a magnifying glass.

Picture by anjrued via Flickr

6 Comments

1. 1. jack.123 07:12 PM 5/27/09

   Can you say fraud?House would't sell?

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2. 2. acutar@gmail.com 04:17 PM 5/29/09

   What is more sad? That a person might commit arson by any means or that we can't read an innocent article aimed simply at the unique possibility of a "dog bowl caused fire" without imediately assuming the worst about the home owner? Tell me if I am wrong, but the subject of the article was whether such an event was possible and under what conditions it might occur? Correct? DG

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3. 3. jack.123 07:02 PM 5/29/09

   The elements that happened in this event are random,except for the dish being 14" above the deck.What ever the mesh was made of that the dish was sitting on it must have been transparent,perhaps holding it just on the edges, and leads to the question why a stand,maybe it was nice to look at.If this was arson, it was very well thought out indeed,hopefully this isn't the case, but it is at the very least suspicious,a lightning strike is more plausible.One must alppaud the Bellevue Fire Department for doing the experiment.Something CSI would have been prould of.

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4. 4. ShastaRedbud 01:52 AM 5/31/09

   We once had a round fishbowl (actually a cookie jar) but it was perfect for our goldfish, Cleo. He had been happy sitting at the kitchen table for years, until we started doing nightly bookkeeping there. The loud clicking of the adding machine made him go a little nuts! So, we moved the bowl into the living room. We put it on an end table, between two chairs, with a large "picture" window directly behind it. Thought he might enjoy the view! The bowl had only been in it's new spot for a day or two. It was a pretty day...sunny. I opened the curtains and about noon, as I recall, I was sitting in the chair next to the fishbowl, reading. I noticed smoke rising about 3 inches above the end table, next to the fishbowl. I immediately got out of my chair and looked at it! There was already a black mark on the mahogany table! It was slowly burning! I gingerly touched the fishbowl. It was still cool and Cleo was fine. It didn't affect either of them but if I hadn't been right there to see it, I wouldn't have believed it! Cleo went back to the kitchen table...and was happy there.

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5. 5. rideHPD 02:32 PM 5/31/09

   Dog owners typically put their pet's food and water on stands to relieve neck strain from bending down to eat. And that is a very impressive coagulation fire reactants, considering that there is only a small window in which the distance between the bowl and kindling have to coincide with the bowls index of refraction.

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6. 6. rwilliston 04:41 PM 6/1/09

   I don't know why anyone should be surprised, this is very simple optics. I do wonder if arson charges shouldn't be laid, if not against the homeowner, at least against the bowl manufacturer. If this bowl was indeed specified for dog use, then it would be perfectly reasonable that some owners might put it outdoors. There should be a warning sticker on every bowl stating not to use A GIANT LENS outdoors.

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