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Science people - how did my house not blow up?


AmandaVT
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So I am profoundly grateful that I am sitting in my kitchen next to my 8 year old right now. This past weekend, DH and I went out for the evening, leaving DS with my mom watching him. She is a very responsible person, and overly cautious as a rule. 

 

That evening, one of them accidentally turned the knob on our range and turned the propane on - neither noticed. It was on (no flame, just propane) for at least 3 hours, slowly filling the house up with a horrible smell. It must have creeped up on them, because somehow, neither one of them really smelled much. 

 

At one point, my mom smelled it and assumed (?!?) we had made broccoli or brussel sprouts earlier in the day and she was smelling that, so she lit a candle right next to the burner that was leaking propane. 

 

DH and I returned home and were immediately hit with the incredibly strong smell of propane. Mom and DS were happily sitting on the couch, watching a movie, totally oblivious. We turned off the stove, blew out the candle and opened every window and door in the house to air it out. We had DS and mom stand by the door to breathe in the outside air and DH called poison control to see if we needed to take them to the ER for exposure or anything (no). It was so strong - every corner of the house smelled, DH and I were almost gagging from the smell.

 

They're fine, my mom is horrified of course, but they're fine. The house is fine.

 

But DH and I can't figure out why the candle being lit didn't create an explosion. We are incredibly grateful of course to be perplexed by a science problem rather than planning funerals, but isn't propane incredibly explosive? Is there a science explanation for this? Or should I keep giving my grandma the credit for keeping them safe (she passed away in 2002). 

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The only thing I can think of is that propane is heavier than air so the worst of it would have been closer to the ground?  

 

I also read this:

 

Propane has a flammable range of 2% to 10%, he said.

“Anywhere in that range you will have an explosion. Whether it’s a small explosion or a big one depends on the area and concentration. If you are under [2%], you won’t have ignition; if you’re over [10%], you won’t have ignition because it’s either too lean or too rich,†he said.

That close to the stove, the concentration may have been over 10% and out of the ignition range?

We have a propane stove as well and I worry about this constantly,especially because our knobs are on the front edge.  Our microwave and a cabinet sit over the stove and I have accidentally turned the knobs while reaching over in the past.  It's why I won't let my kids even use the microwave when no one is there to watch them.  They are shorter and more likely to bump the knobs.

I'm glad everything was okay.

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The only thing I can think of is that your Mom lit the candle before the air was fully saturated, so there was enough clean air to not ignite the propane all at once.

 

I'm so glad everyone is ok! How scary!!

 

ETA: Toto has a better explanation. We were cross-posting.

Edited by fraidycat
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First, the reason they didn't smell it is because you stop smelling the stuff they put in the propane to make it smell after only a few minutes.  

 

Propane needs to be at a particular concentration in order to ignite.  Also, my understanding is that it is dense, so it will fill a room from the bottom up.  Perhaps the candle was far enough off the ground so that it was out of the area where the propane was.

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A drafty house, high winds, cold outside temps, running furnace, etc will all mix the air up and change the air enough (HOPEFULLY) to keep it from reaching the lower explosive limit.  

 

Possibly the tank is low and the concentration of odorant is higher than if the tank was full?  It seems like LP has a greater smell than natural gas also, as it should because it is more explosive.

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Thanks for the replies and good wishes!

 

Tanks just got filled last week, so it's pretty full. The stove is downstairs (candle was on top of the stove - literally next to the burner). Upstairs was totally filled with gas as well. It was really potent. 

 

EKS - that's good to know about the smell not being, smelly (for lack of a better word) after a few minutes. I know that'll make my mom feel a bit better when I tell her. She is distraught about it still and is still beating herself up over what happened. 

 

House isn't drafty at all, but it was quite cold out that night, less than 10 degrees.

 

I'm thinking the concentration must have been too high for anything to ignite. 

 

So scary! I'm glad we got home when we did and didn't go out for a drink or anything after our party. 

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As people age, our sense of smell is also impaired. 

 

I'm so very glad nothing terrible happened!!
 

If I were you, I'd go ahead and invest in some sort of alarm system for the gas. I just googled and found many options, generally under $50. I'd go ahead and invest in some, to give you all peace of mind!!  

 

Wow, what a miracle!

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As people age, our sense of smell is also impaired. 

 

I'm so very glad nothing terrible happened!!

 

If I were you, I'd go ahead and invest in some sort of alarm system for the gas. I just googled and found many options, generally under $50. I'd go ahead and invest in some, to give you all peace of mind!!  

 

Wow, what a miracle!

 

That is a great idea. We have smoke alarms and carbon monoxide detectors, but I hadn't thought of an alarm system for gas. 

 

She's in her early 60's and in very good health, but age could be a factor. I did (very gently) remind her that if she ever smells something funny, to not assume that people randomly made brussel sprouts and to check obvious places like the stove to make sure nothing is leaking!

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That is a great idea. We have smoke alarms and carbon monoxide detectors, but I hadn't thought of an alarm system for gas.

 

She's in her early 60's and in very good health, but age could be a factor. I did (very gently) remind her that if she ever smells something funny, to not assume that people randomly made brussel sprouts and to check obvious places like the stove to make sure nothing is leaking!

Just an FYI on the gas alarms- if you get one, be very careful on where you place it. Nail polish and remover, dog and human gas and other similar smells can set it off. Really not fun at 3am when you dog has set it off.

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Didn't Mythbusters do something along these lines? If I recall, they had to have a lot of gas in the air before it would ignite.

 

A little alcohol will set them off.  I'm sure nail polish remover will to.  The smell from dogs etc. doesn't set them off, it's the methane content, and there's not that much methane in a dog, usually.  Any house with gas should have a CO/explosive gas alarm, it's code in most places as far as I know. 

 

There's no way the gas was over the limit, the candle would have burned three feet high or starved out.  The smell does not directly correlate with the gas concentration, just ask the backseat passengers in a stinky car with an alarm that's not going off.  

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A little alcohol will set them off. I'm sure nail polish remover will to. The smell from dogs etc. doesn't set them off, it's the methane content, and there's not that much methane in a dog, usually. Any house with gas should have a CO/explosive gas alarm, it's code in most places as far as I know.

 

There's no way the gas was over the limit, the candle would have burned three feet high or starved out. The smell does not directly correlate with the gas concentration, just ask the backseat passengers in a stinky car with an alarm that's not going off.

Trust me on the dog gas. We were able to recreate it. She was a special dog who had an unfortunate love of broccoli. Lol

 

Where I live, only a CO and fire alarm are required.

Edited by itsheresomewhere
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Dh said it's most likely because the gas to air ratio was to low. When the candle was lit, the air concentration would have been to low to ignite. The smell is an additive meant to be strong to raise awareness of a leak, however, you can't judge how much gas is in the house based on the smell. Not sure if that helps.

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We had a high pressure gas line cut right in front of our house once and blow natural gas right into our home. There were rocks pelting the house with it so DH and I were staring at each other in a panic trying to figure out what on earth was going on. It took us 20-30 seconds to realize it was gas because at high concentrations (I now know fist hand) the additive does not smell the same. It totally does smell broccoli like your mom said.

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Don't know if you remember, but we had a house fire last summer caused by a candle igniting methane.  My daughter was cleaning out a freezer she accidentally defrosted and left a candle burning very near the open freezer while she went upstairs to shower.  The refrigerator ignited first and burned for almost 30 minutes before the cabinets caught fire.  That's when she realized the house was burning and got out.  We did have an explosion, but I'm pretty sure the backdraft contributed because it happened just after she left the house. All the windows blew out and the built in microwave wound up in the family room, but even after all that the house itself is still standing.  Gutted, but standing.  

 

It takes a lot more gas to blow up a building than it does in the movies, lol.

 

 

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