How much energy was expended when my stove blew up?
November 3, 2019 9:54 AM Subscribe
One of the burners on our electric stove blew up (will explain further). I am curious to know certain estimates, like: how hot it may have been, the amount of TNT it was equivalent to, and the amount of UV and IR radiation that might have been emitted.
On Friday, I was upstairs when I heard a very loud buzzing that lasted about 5 or 10 seconds. I wasn't sure what it was until I realized it was the sound of electricity arcing. I went downstairs to find a pan burning with a hole in it (someone else had been cooking). We are incredibly lucky that no one was in the kitchen at the time, and that the explosion was directed towards the back of the stove.
Someone came and checked it out and said that the heating element inside the burner must have cracked and arced, blowing out the ceramic coating. It was basically an arc welder for a few seconds, right?
This is consistent with a few things. Someone was just outside the kitchen doorway, and they said that there was a very bright light.
The stove coil itself was blown apart. You can see where the ceramic was melted, and the metal coil itself seems to have been ejected towards the wall. The pan that was on that burner had a hole burned in it so quickly that it was still half-full of water when we got to it.
Lastly, there are intense burns on the back of the stove. I think these must be steam burns from the water. There is a spray of black spots going up the wall, and I suspect these are either bits of molten ceramic, bits of molten metal from the pan or the heating element itself, or some combination of all three.
Is it possible to estimate some of the energy involved? Like I said, I'd like to know:
-how much energy was likely expended (bonus if it can be compared to a TNT equivalent)
-how hot that point may have been
-how much UV and IR radiation may have been emitted, in addition to the intensity of the visible light
-any other fun science facts you may be able to estimate
The best I can do at the moment is estimate how much current the stove draws. It's an older stove, so I don't know if that's a factor. It's plugged in to a 220V socket, and it did trip the breaker (should I see what the breaker is rated for?). Like I said, it sounded to me like it was arcing for a good 5 seconds or so, if that would be a factor.
Let me know if there's any other information you may need! I totally understand if this is a largely unanswerable question, if there are too many unknown variables.
On Friday, I was upstairs when I heard a very loud buzzing that lasted about 5 or 10 seconds. I wasn't sure what it was until I realized it was the sound of electricity arcing. I went downstairs to find a pan burning with a hole in it (someone else had been cooking). We are incredibly lucky that no one was in the kitchen at the time, and that the explosion was directed towards the back of the stove.
Someone came and checked it out and said that the heating element inside the burner must have cracked and arced, blowing out the ceramic coating. It was basically an arc welder for a few seconds, right?
This is consistent with a few things. Someone was just outside the kitchen doorway, and they said that there was a very bright light.
The stove coil itself was blown apart. You can see where the ceramic was melted, and the metal coil itself seems to have been ejected towards the wall. The pan that was on that burner had a hole burned in it so quickly that it was still half-full of water when we got to it.
Lastly, there are intense burns on the back of the stove. I think these must be steam burns from the water. There is a spray of black spots going up the wall, and I suspect these are either bits of molten ceramic, bits of molten metal from the pan or the heating element itself, or some combination of all three.
Is it possible to estimate some of the energy involved? Like I said, I'd like to know:
-how much energy was likely expended (bonus if it can be compared to a TNT equivalent)
-how hot that point may have been
-how much UV and IR radiation may have been emitted, in addition to the intensity of the visible light
-any other fun science facts you may be able to estimate
The best I can do at the moment is estimate how much current the stove draws. It's an older stove, so I don't know if that's a factor. It's plugged in to a 220V socket, and it did trip the breaker (should I see what the breaker is rated for?). Like I said, it sounded to me like it was arcing for a good 5 seconds or so, if that would be a factor.
Let me know if there's any other information you may need! I totally understand if this is a largely unanswerable question, if there are too many unknown variables.
The difficulty is that the breaker tripped after an unknown amount of current went through. So although time may be known, power is not -- though there's an upper bound, past which the wires in the wall would have burned out. Breakers don't just blow when e.g. 10.1 amps go through a 10 amp breaker. There's delay and heating and other factors.
So any answer you get is going to be very, very ballpark, but probably somewhere between 5sec * 3000W (approx rating for stove) (15K joules) and let's say four times that, 60K joules.
Taking the high figure, 60K joules, that's equivalent to 14kcal. Or about as much energy as are in 3 Reese's Pieces.
posted by seanmpuckett at 10:04 AM on November 3, 2019
So any answer you get is going to be very, very ballpark, but probably somewhere between 5sec * 3000W (approx rating for stove) (15K joules) and let's say four times that, 60K joules.
Taking the high figure, 60K joules, that's equivalent to 14kcal. Or about as much energy as are in 3 Reese's Pieces.
posted by seanmpuckett at 10:04 AM on November 3, 2019
Response by poster: I'm having a hard time understanding how to mentally convert between calories as in food, and calories as in energy.
I'm reading up on a few things, and I guess the coil is probably not ceramic, but hollow steel with a heating element inside. If that's the case, then the melting point for that coil would be around 2500 degrees F right? It looks more like steel to me, and I guess it's safer to err on the side of caution, since the melting point of a vitrified ceramic would probably be higher.
So if I'm thinking in terms of delicious candy, should I think about the energy required to... burn that? At a focused spot? To reach a minimum of 2500 degrees?
posted by shapes that haunt the dusk at 10:19 AM on November 3, 2019
I'm reading up on a few things, and I guess the coil is probably not ceramic, but hollow steel with a heating element inside. If that's the case, then the melting point for that coil would be around 2500 degrees F right? It looks more like steel to me, and I guess it's safer to err on the side of caution, since the melting point of a vitrified ceramic would probably be higher.
So if I'm thinking in terms of delicious candy, should I think about the energy required to... burn that? At a focused spot? To reach a minimum of 2500 degrees?
posted by shapes that haunt the dusk at 10:19 AM on November 3, 2019
Calories in food are in reality Kilo-calories. So to convert, divide the Nutrition Label info by 1,000 to get real, Physics calories.
I had something similar happen in an old electric stove, many years ago; only in my case it was the upper heating element in the oven. No detonation, just started arcing and burning at one end, and like a fuse, it had to burn all the way to the other end before it finally went out. (Note that directing a fire extinguisher into the oven only made a mess and made the kitchen's air even more unbreathable.) The next day the electrician shrugged his shoulders and said, "It happens, sometimes."
posted by Rash at 11:03 AM on November 3, 2019
I had something similar happen in an old electric stove, many years ago; only in my case it was the upper heating element in the oven. No detonation, just started arcing and burning at one end, and like a fuse, it had to burn all the way to the other end before it finally went out. (Note that directing a fire extinguisher into the oven only made a mess and made the kitchen's air even more unbreathable.) The next day the electrician shrugged his shoulders and said, "It happens, sometimes."
posted by Rash at 11:03 AM on November 3, 2019
Circuit breakers don't instantly disconnect when the nameplate current rating is exceeded, they have a time-current curve. In the US residential circuit breakers will disconnect "instantaneously" (under 0.1 seconds) when the current exceeds 4x their rating in amps, under 5 seconds at 4x, several minutes at 2x, and 15 minutes or more just over their rating. Oven circuits in the US are usually protected by a 2-pole 50 amp residential circuit breaker.
If we assume all the energy of your "explosion" came from the excess heating during the arcing, ignoring the latent heat or any combustion of the heating element, and the arcing current was just under the instantaneous disconnect current of the breaker, we might estimate the energy was 240 volts * (50 amps *4) * 5 seconds which equals 53.33 Watt hours or 192 kilojoules.
192 kilojoules is equivalent to the energy released by exploding about 46 grams of TNT. Also, 192 kilojoules is 45889 "small" calories or about 46 food calories, about equivalent to the energy in a cookie. Sugar is actually a really good way to store energy as the energy density of sugar is about four times that of TNT. What is is special about TNT is that it burns fast.
Calories in food are in reality Kilo-calories. So to convert, divide the Nutrition Label info by 1,000 to get real, Physics calories.
Multiply food calories by 1000 to get calories.
posted by RichardP at 1:01 PM on November 3, 2019 [9 favorites]
If we assume all the energy of your "explosion" came from the excess heating during the arcing, ignoring the latent heat or any combustion of the heating element, and the arcing current was just under the instantaneous disconnect current of the breaker, we might estimate the energy was 240 volts * (50 amps *4) * 5 seconds which equals 53.33 Watt hours or 192 kilojoules.
192 kilojoules is equivalent to the energy released by exploding about 46 grams of TNT. Also, 192 kilojoules is 45889 "small" calories or about 46 food calories, about equivalent to the energy in a cookie. Sugar is actually a really good way to store energy as the energy density of sugar is about four times that of TNT. What is is special about TNT is that it burns fast.
Calories in food are in reality Kilo-calories. So to convert, divide the Nutrition Label info by 1,000 to get real, Physics calories.
Multiply food calories by 1000 to get calories.
posted by RichardP at 1:01 PM on November 3, 2019 [9 favorites]
Temperatures of arcs are crazy high, up to 35,000 °F.
Way hotter than the melting point of anything on Earth.
posted by jamjam at 1:35 PM on November 3, 2019
Way hotter than the melting point of anything on Earth.
posted by jamjam at 1:35 PM on November 3, 2019
TNT also contains its own oxidizer; a gram of sugar requires several grams of oxygen to burn, while a gram of TNT is self-contained.
posted by Hatashran at 3:43 PM on November 3, 2019
posted by Hatashran at 3:43 PM on November 3, 2019
I think you need a physicist, or maybe an EE, to answer the question, but I once observed something similar which may help with the chain of events. Or maybe your events were different.
So, spoiler alert, the thermostat on one burner of an electric stove failed so that the power never turned off when the burner reached it's designed temperature. The sequence was that the heating coil turned red, then white, then melted, and finally the heat defeated the insulation on the wires, and there was arcing. I don't remember if it process stopped by itself, or if the electricity was turned off. We did not have as much of an explosion or as much damage to the stove and surrounding as you describe.
posted by SemiSalt at 5:44 PM on November 3, 2019
So, spoiler alert, the thermostat on one burner of an electric stove failed so that the power never turned off when the burner reached it's designed temperature. The sequence was that the heating coil turned red, then white, then melted, and finally the heat defeated the insulation on the wires, and there was arcing. I don't remember if it process stopped by itself, or if the electricity was turned off. We did not have as much of an explosion or as much damage to the stove and surrounding as you describe.
posted by SemiSalt at 5:44 PM on November 3, 2019
As far as UV is concerned, a black body with an emissions peak of 350 nm (~near-ultraviolet) will have a temperature between 14,000 - 15,000 °F, so if your arc was anywhere near the 35,000 °F range, it emitted a lot of UV.
posted by jamjam at 8:21 PM on November 3, 2019
posted by jamjam at 8:21 PM on November 3, 2019
This thread is closed to new comments.
posted by shapes that haunt the dusk at 9:57 AM on November 3, 2019