How do dropped cigarettes start house and brush fires?

Now this sounds like a really dumb question until you have some practical experience with the problem. As a former teenage smoker, I tried to intentionally start dozens of fires using cigarettes with newspapers, straw, hay and anything else I could find. I never suceeded. Then, I started winning bets that other people could not do it. My favorite was to pour some gasoline on the ground and tell people that they could not light it by throwing a cigarette on it. Then we moved to a small bucket filled with gasoline. No one could ever do it. The cigarette simply went out. I understand that you can make a gasoline explosion by holding your face over the bucket and inhaling hard but I never let anyone get that close.

That makes me wonder how all of these house and brush fires that we hear about on the news are started by cigarettes? No one ever questions them or explains. It is just assumed that hot cigarette equals fire. I believe that it is the cigarette that starts the fire because I can’t think of what else it could be but I can’t figure out how it starts.

I would imagine that if you have a decent kindling chain then you can get it going. (dry conditions, pine needles/leaves &twigs in the forest, appropriately placed papers or flammables in the house). The reason your spilled gasoline expermient may have failed could be due to the cigarette entering an all-fuel vapor environment - insufficient oxygen locally to ignite or sustain.

Still, gasoline is not a substance I would conduct random outdoor combustion experiments with.

I would say that having a breeze is critical. As you observed, a lit cigarette just sitting there isn’t much of a lighter. Even to light another cigarette with it you have to suck on it – the airflow both intensifies the combustion and helps move the heat toward what’s being lit. But with the right breeze and the right configuration of tinder, it could start a fire.

I once dropped a cigarette on my dorm room mattress without realizing it. It slowly burned into the stuffing, and smoldered for some time (an hour or two?). I then sat on the mattress, which acted like a bellows, and a good-sized area of it glowed intensely. If I’d pumped on the mattress a few times, I’m sure it would have erupted into flame.

Those of you who have built campfires have probably experienced this. Sometimes it’s necessary to fan it into flames.

I suspect, however, that in many cases of fires said to be started by cigarettes, there’s no direct evidence of that. I imagine cigarettes get blamed because they’re the only reasonably likely cause.

I’ve started a fire by accidentally flicking a burning ash onto a leaf. Fortunately the wind wasn’t blowing and I smelled it inside the house when it had only lit a few other leaves on fire.

I agree that cigarettes are often blamed because they don’t know how the fire started, and smokers are an easy target. Years ago, I very large brush fire that turned into an urban fire was blamed on a cigarette, and I never heard any evidence for this.

Except that smokers have been warned to be careful about the hazards of cigarette caused fires since long before smoking began to be publicly condemned. So it’s not just something they say to pick on smokers. Smoking in bed was always the big thing to avoid doing, lest you fall asleep and drop a lit cigarette in the covers. It can definitely happen. My mother fell asleep while smoking and sitting on a sofa, and the sofa caught fire, giving her the final push she needed to quit.

One time my sister was smoking on the porch, and put her cigarette out in a flower pot full of dried up dirt. She went on with whatever she was doing inside until I smelled something burning. I looked outside and noticed that the flower pot was smoking. Apparently the dirt itself had started smoldering and eventually melted the flower pot. It took several glasses of water to put it out.

As MMI says, that all-fuel environment won’t burn, since there’s no oxygen. (In fact, the cig in a bucket of gasoline is a standard macho trick in some circles.) With any sort of air circulation, the gasoline vapour never builds up to a flammable level. Note that there are a few fuels that carry their own oxidizer, but most of them are explosives.

As to cigarettes starting fires, I’ve seen it happen the same way cornflakes did, luckily also with no damage. I’ve also seen an arson-igniter setup using a cig to start it, but I’ll omit the details. It worked well in the demo, though!

Well, for what it’s worth, I’ve seen a few ashcan fires (and started a couple myself), resulting in smoldering, very smoky fires, and (when enough trash was in the ashcan) flames.

Smoking in bed is a common cause of house fires; one reason we know this is because sometimes people survive and know what happened. By comparing burn patterns and whatnot to fires from known causes, professionals can often determine whether a fire of unknown cause was likely to have originated with a cigarette. “Likely” is an important word - freak accidents do happen, but training and research improves their accuracy every year when a cause is later determined for certain.

So, often, we don’t know for a fact that a given fire was caused by a cigarette. But they aren’t just making up guesses; their training is based on comparitive data, and probably often confirmed with multiple techniques.

I’m speaking in fairly broad generalities to cover the fact that I’m really just talking out of my ass, aside from reading a few news articles that I Googled up. I’m sure there’s firefighters and other experts who can fill in the details.

I read someplace that birds will sometimes pick up cigarette butts and bring them back to their nests. If the butt is still lit, and if the nest is in the eaves of a house, a fire can result.

Is there anything to this, or is it another razor-blade-in-the-apple type story?

Exhaling hard over a bucket/can of gasoline would provide the mix of air and gas vapor to ignite or explode.

Inhaling hard over the liquid gasoline and vapors would likely make you a candidate for ressusitation and a trip to the E.R.

Gasoline and air make a dangerous explosive mixture and is not a plaything or toy.

Yep: two months before my 6th birthday, the apartment building my family was living in had a huge fire in the middle of the night. We, along with many other families, lost nearly everything (including our cat). I don’t believe any of the building tenants died because of that fire (one fireman did die after falling through the roof while venting the building; I had gone into shock, and was put in the same ambulance with him…while he was still alive, of course…but that’s another story), but the cause was proven to be a lit cigarette dropped by an upstairs neighbor who fell asleep while smoking.

So have no doubt, Shagnasty: many things that resist deliberate creation (like a fire started by a cigarette) happen by accident quite frequently. :slight_smile:

Playing with gasoline is definitely Russian Roulette. It may not explode this time, or the next time, but when it does, you are going to be very sorry you ever used it for a play thing.

The same thing happened to me one time! A cigarette is basically a smoldering mass of shredded vegetation. So is the topsoil in a forest. Thus, topsoil can begin smoldering just as if it were a cigarette. When the smoldering mass is large enough, sufficient heat is generated to actually ignite something. That’s one way this can happen.

Most forest fires (at least in my area) and presumably many brush fires are started by lightning, not by human activity. Of the fires started by humans, some are deliberate, some are started by campfires, and some are started by cigarettes. A cigarette might not be hot enough to start a forest fire before burning out under many conditions, but with a breeze and sufficiently dry plant material I can see how a fire might start.

The real issue isn’t that a very large percentage of brush and forest fires are started by careless smoking (or campfires, for that matter) – it’s that these fires are preventable. Forest fires are very destructive, and the media usually stresses the cause if the fire was preventable. When forest fires are caused by lightning, they often don’t give the cause.

With house fires, I agree that they may blame smoking if the victim was a smoker and the cause can’t be determined otherwise. If the fire is contained or put out in time, though, there are ways of determining where the fire started. A plume of soot on a wall above an ashtray, for example, might suggest a fire started by a cigarette.

What about spontaneous combustion? When I was a child, we were often warned about fires started by oily rags. It’s been years since I’ve heard anyone mention it, except for an instructor for oil painting, who warned us about the danger of linseed oil soaked rags.

Concerning the spontaneous combustion: You need Heat, Fuel and Oxygen for a fire to burn. With an oily rag, you already have fuel (oil) and oxygen (air); all you need is it to become warm enough to ignite. Many oils, solvents and petrochemicals will ignite below 150°F. Just being near a pilot light or a warm stove is enough. Or ask my friend who left a box of oily rags on the backseat of his car in direct sunlight during an Alabama summer.