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Speaking of spontaneous combustion - ammonium nitrate will spontaneously ignite in the presence of some impurities. Ammonium nitrate plus zinc powder is a mixt

Speaking of spontaneous combustion - ammonium nitrate will spontaneously ignite in the presence of some impurities. Ammonium nitrate plus zinc powder is a mixture that only needs a drop of water or just sufficiently humid air to ignite.

mindcrime 6y ago
Another one is just plain ole organic matter, like mulch. Back in my days as a firefighter, our district included the county landfill. After one of the hurricanes that came through, they had gone around collecting all the downed trees, and chipped them up into mulch, and located this HUGE pile of mulch at the landfill, where county residents could come and get free mulch / wood chips for their gardens or whatever. Sounds great, right? Except it turns out that a huge mountain of decaying organic matter, left exposed to the southeast NC sun in July and August will periodically catch fire spontaneously. We went out there a few times to put that mess out. Not an easy task. You have to bring in heavy machinery to dig into the piles in order to get to the seat of the fire...and of course the landfill was nowhere near a hydrant, so we had to call out half the tankers in the county to set up a tanker shuttle... uuugggh.
- jacquesm 6y ago
  The sun is actually not much of a factor in there. What makes this happen is that the mulch rots which is an exothermic process and it insulates very good as well. So the core temperature of pile will slowly creep up until you reach the ignition point. The same will happen to bales of hay that are taken from the field too wet.
  - chasd00 6y ago
    bales of rotting wet hay is where barn fires come from.
    - jacquesm 6y ago
      Yep. They also sometimes spontaneously combust in the field.
      - mindcrime 6y ago
        Yes they do. We went to more than a few hay bale fires as well. Those are also a pain in the ass, and for similar reasons.
        jacquesm 6y ago
        So what's the procedure like? Pull them apart and then put it out? I'd assume that if you just wet them from the outside you are just setting yourself up for a speedy return to the same location.
        mindcrime 6y ago
        So what's the procedure like? Pull them apart and then put it out? Exactly. Besides trapping heat in, the hay also forms a fairly effective barrier against water getting inside. If you don't rip the bale apart to fully extinguish the seat of the fire, you just wind up right back out there. You can see the process underway in this video, where a bunch of hay bales caught file while on the back of a truck being transported. Scroll a few minutes into the video and you can see where they brought a front-end loader out there to start ripping the bales apart. Using a "wetting agent"[1] also helps, and some departments will use store bought dish soap, like Dawn, for that purpose (purpose made firefighting foam is kinda expensive). https://youtu.be/z1_pAH34wAo https://youtu.be/z1_pAH34wAo [1]: https://en.wikipedia.org/wiki/Surfactant https://en.wikipedia.org/wiki/Surfactant
        jacquesm 6y ago
        Interesting video, especially with a drone over so much hot air. Amazing how much land is already gone. And the truck itself is just a memory while plenty of the bales of hay are still sitting around unharmed, you can really see the 'R' value at work there. It almost looks as though the fire started in the truck itself or on one of the rear brakes, was there a report on the cause of the fire in this particular case? edit: amazing coordination as well, at one point working on the fire in four different places.
  - mindcrime 6y ago
    What makes this happen is that the mulch rots which is an exothermic process and it insulates very good as well. So the core temperature of pile will slowly creep up until you reach the ignition point. Absolutely true. But while I wouldn't even be able to begin quantifying the degree to which the radiant heat from the sun is a factor, I strongly suspect that it is a factor, if for no other reason that the observation that we only went to those fires in summer months. But, to be fair, there could be a million other confounding factors. Whether or not a given system ignites on a given day depends on many things: ambient temperature, wind, humidity, presence of accelerants, yadda, yadda, yadda. I suspect this is one reason why it's so hard to get people to take fire safety seriously: that pile of oily rags in the corner? It's not going to catch fire. This time. Or next time. Or next time. And so on... until it does. So people get complacent because "hey, the oily rags never caught fire before, why would I expect them to today?" Disconnect the sprinkler system? Sure, why not - the building isn't going to catch fire. This time...
    - jacquesm 6y ago
      I know the former head fire marshall of a major European city (2M inhabitants). The stories about root causes have made me extra fire safety sensitive and it is a continuous source of frustration to me that others don't take this stuff as serious. Cheap power adapters are somewhere near the top of my paranoia list, anything rechargeable battery operated a close second.
  - thehappypm 6y ago
    Fun fact, the metabolism of the sun produces about as much energy per unit volume as a pile of mulch.
- userbinator 6y ago
  You have to bring in heavy machinery to dig into the piles in order to get to the seat of the fire Wouldn't that expose more of it to oxygen and thus increase the fire's strength? Or does it generate oxygen itself?
  - mindcrime 6y ago
    Wouldn't that expose more of it to oxygen and thus increase the fire's strength? Yes, but there really isn't much else in the way of practical choices. If you had some 100% bullet-proof way to seal the fire off from any oxygen, then eventually it would go out and cool below it's ignition temperature. But "bury it in sand (or concrete)" isn't a practical solution for the average fire. Beyond that, you could play around with piercing nozzles and more wetting agents / foam and what-not and try to avoid digging the pile up, but generally speaking those things would be too time consuming for the typical fire department. Consider that any time you're on a call, that apparatus and crew are not available to respond to other, perhaps more urgent, calls. So fire departments typically try to avoid spending excess time on the scene of a relatively low hazard fire like a mulch pile. You can't just ignore it completely, because embers from that fire could then spread and cause another fire, etc. So you have to show up and deal with it, but you want to get done as soon as possible. A private / industrial fire brigade might take a different approach, because they are operating under different constraints. All of that said, there is one particular case where "bury it in sand" might be used in a setting that a typical municipal FD might run into. That case would involve a Class D (flammable metals)[1] fire. Those are notoriously hard to extinguish and "bury it" is a valid option. So if a FD had some industrial areas in their district, where a factory was, say, making something out of magnesium or another flammable metal, and somehow managed to catch a load of the stuff on fire, it's entirely possible that the response would be "Call in DOT (or whoever) and have them bring a couple of dump truck loads of sand to the scene". There are specialized fire extinguishers for this stuff[2], but they're expensive, only contain so much extinguishing agent, and aren't - in my experience - commonplace on fire apparatus. In practice, this situation doesn't come up terribly often. And a plant or factory working with lots of flammable metals in high volume might well have a private industrial fire brigade that specializes in fighting those fires. [1]: https://en.wikipedia.org/wiki/Fire_class#Metal https://en.wikipedia.org/wiki/Fire_class#Metal [2]: https://www.monroeextinguisher.com/product/ansul-redline-30-lb-metal-x-dry-chemical-cartridge-fire-extinguisher/ https://www.monroeextinguisher.com/product/ansul-redline-30-...
- dredmorbius 6y ago
  Spreading woodchips dumped shortly before first snow some years back, I noted on a well-below-freezing day that the centre of my woodchips pile was straming & smoking. Chips melted through a few inches of snow when laid down on garden paths, and remained clear of snow for at least several days. No explosions.

mindcrime 6y ago

Another one is just plain ole organic matter, like mulch. Back in my days as a firefighter, our district included the county landfill. After one of the hurricanes that came through, they had gone around collecting all the downed trees, and chipped them up into mulch, and located this HUGE pile of mulch at the landfill, where county residents could come and get free mulch / wood chips for their gardens or whatever. Sounds great, right? Except it turns out that a huge mountain of decaying organic matter, left exposed to the southeast NC sun in July and August will periodically catch fire spontaneously. We went out there a few times to put that mess out. Not an easy task. You have to bring in heavy machinery to dig into the piles in order to get to the seat of the fire...and of course the landfill was nowhere near a hydrant, so we had to call out half the tankers in the county to set up a tanker shuttle... uuugggh.

jacquesm 6y ago
The sun is actually not much of a factor in there. What makes this happen is that the mulch rots which is an exothermic process and it insulates very good as well. So the core temperature of pile will slowly creep up until you reach the ignition point. The same will happen to bales of hay that are taken from the field too wet.
- chasd00 6y ago
  bales of rotting wet hay is where barn fires come from.
  - jacquesm 6y ago
    Yep. They also sometimes spontaneously combust in the field.
    - mindcrime 6y ago
      Yes they do. We went to more than a few hay bale fires as well. Those are also a pain in the ass, and for similar reasons.
      - jacquesm 6y ago
        So what's the procedure like? Pull them apart and then put it out? I'd assume that if you just wet them from the outside you are just setting yourself up for a speedy return to the same location.
        mindcrime 6y ago
        So what's the procedure like? Pull them apart and then put it out? Exactly. Besides trapping heat in, the hay also forms a fairly effective barrier against water getting inside. If you don't rip the bale apart to fully extinguish the seat of the fire, you just wind up right back out there. You can see the process underway in this video, where a bunch of hay bales caught file while on the back of a truck being transported. Scroll a few minutes into the video and you can see where they brought a front-end loader out there to start ripping the bales apart. Using a "wetting agent"[1] also helps, and some departments will use store bought dish soap, like Dawn, for that purpose (purpose made firefighting foam is kinda expensive). https://youtu.be/z1_pAH34wAo https://youtu.be/z1_pAH34wAo [1]: https://en.wikipedia.org/wiki/Surfactant https://en.wikipedia.org/wiki/Surfactant
        jacquesm 6y ago
        Interesting video, especially with a drone over so much hot air. Amazing how much land is already gone. And the truck itself is just a memory while plenty of the bales of hay are still sitting around unharmed, you can really see the 'R' value at work there. It almost looks as though the fire started in the truck itself or on one of the rear brakes, was there a report on the cause of the fire in this particular case? edit: amazing coordination as well, at one point working on the fire in four different places.
- mindcrime 6y ago
  What makes this happen is that the mulch rots which is an exothermic process and it insulates very good as well. So the core temperature of pile will slowly creep up until you reach the ignition point. Absolutely true. But while I wouldn't even be able to begin quantifying the degree to which the radiant heat from the sun is a factor, I strongly suspect that it is a factor, if for no other reason that the observation that we only went to those fires in summer months. But, to be fair, there could be a million other confounding factors. Whether or not a given system ignites on a given day depends on many things: ambient temperature, wind, humidity, presence of accelerants, yadda, yadda, yadda. I suspect this is one reason why it's so hard to get people to take fire safety seriously: that pile of oily rags in the corner? It's not going to catch fire. This time. Or next time. Or next time. And so on... until it does. So people get complacent because "hey, the oily rags never caught fire before, why would I expect them to today?" Disconnect the sprinkler system? Sure, why not - the building isn't going to catch fire. This time...
  - jacquesm 6y ago
    I know the former head fire marshall of a major European city (2M inhabitants). The stories about root causes have made me extra fire safety sensitive and it is a continuous source of frustration to me that others don't take this stuff as serious. Cheap power adapters are somewhere near the top of my paranoia list, anything rechargeable battery operated a close second.
- thehappypm 6y ago
  Fun fact, the metabolism of the sun produces about as much energy per unit volume as a pile of mulch.
userbinator 6y ago
You have to bring in heavy machinery to dig into the piles in order to get to the seat of the fire Wouldn't that expose more of it to oxygen and thus increase the fire's strength? Or does it generate oxygen itself?
- mindcrime 6y ago
  Wouldn't that expose more of it to oxygen and thus increase the fire's strength? Yes, but there really isn't much else in the way of practical choices. If you had some 100% bullet-proof way to seal the fire off from any oxygen, then eventually it would go out and cool below it's ignition temperature. But "bury it in sand (or concrete)" isn't a practical solution for the average fire. Beyond that, you could play around with piercing nozzles and more wetting agents / foam and what-not and try to avoid digging the pile up, but generally speaking those things would be too time consuming for the typical fire department. Consider that any time you're on a call, that apparatus and crew are not available to respond to other, perhaps more urgent, calls. So fire departments typically try to avoid spending excess time on the scene of a relatively low hazard fire like a mulch pile. You can't just ignore it completely, because embers from that fire could then spread and cause another fire, etc. So you have to show up and deal with it, but you want to get done as soon as possible. A private / industrial fire brigade might take a different approach, because they are operating under different constraints. All of that said, there is one particular case where "bury it in sand" might be used in a setting that a typical municipal FD might run into. That case would involve a Class D (flammable metals)[1] fire. Those are notoriously hard to extinguish and "bury it" is a valid option. So if a FD had some industrial areas in their district, where a factory was, say, making something out of magnesium or another flammable metal, and somehow managed to catch a load of the stuff on fire, it's entirely possible that the response would be "Call in DOT (or whoever) and have them bring a couple of dump truck loads of sand to the scene". There are specialized fire extinguishers for this stuff[2], but they're expensive, only contain so much extinguishing agent, and aren't - in my experience - commonplace on fire apparatus. In practice, this situation doesn't come up terribly often. And a plant or factory working with lots of flammable metals in high volume might well have a private industrial fire brigade that specializes in fighting those fires. [1]: https://en.wikipedia.org/wiki/Fire_class#Metal https://en.wikipedia.org/wiki/Fire_class#Metal [2]: https://www.monroeextinguisher.com/product/ansul-redline-30-lb-metal-x-dry-chemical-cartridge-fire-extinguisher/ https://www.monroeextinguisher.com/product/ansul-redline-30-...
dredmorbius 6y ago
Spreading woodchips dumped shortly before first snow some years back, I noted on a well-below-freezing day that the centre of my woodchips pile was straming & smoking. Chips melted through a few inches of snow when laid down on garden paths, and remained clear of snow for at least several days. No explosions.