Welcome to IAAI’s August 2009 CFITrainer.Net Podcast. This month, we’ll take a closer look at the dangerous combination of summer heat and oily rags, we’ll examine another side of the rise in vacant home fires, and preview research underway on Australia’s devastating "Black Saturday" brush fires. We’ll also cover the latest in IAAI news.

A recent fire in the UK has drawn attention to oily rags as a fire cause. A garage was destroyed by a fire traced to spontaneous combustion of towels soaked with teak oil that the property owner had used to treat their wood floor. He stored the used towels in the garage and, about 8 hours later, they spontaneously combusted.

This topic is very timely. In the Northern Hemisphere, the dog days of summer are upon us. In many places, summer means more people outside, working on the yard, the house, their cars, and outdoor furniture and structures. The nice weather provides an opportunity to tackle outdoor maintenance and renovation chores that often use oil applied with rags, including linseed oil, teak oil, stains, and paint thinners. These used oily rags, if improperly stored or disposed of, can self-heat and spontaneously combust. Self-heating can be exacerbated by high summer temperatures that heat up non-air conditioned garages and sheds, as well as by high summer humidity that prevents rags from drying quickly.

To learn more about the process of spontaneous combustion of oily rags, we’re joined by David Howitt, Professor of Materials Science at UC Davis College of Engineering. Thanks for joining us David.

DAVID HOWITT: Oh, you’re very welcome.

INTERVIEWER: Under what conditions can this type of spontaneous combustion take place?

DAVID HOWITT: Well typically you need vegetable oils or actually fish oils, although people don’t use fish oil very much. But essentially linseed oil or tung oil, which are the two most common vegetable oils. Both actually do this quite readily at ambient temperatures. I think when they’re talking about teak oil, they’re really just talking about an oil that’s appropriate for teak wood. Teak wood is typically fairly hard, and it’s not a very porous wood, and so it relies essentially on something like a linseed oil based stain to give you some surface color and also to actually form a polymerizing film on the surface. Linseed oil is essentially a natural type of varnish. And these generic paints are becoming more and more popular now. They were very popular years and years ago, but they’re becoming more popular because the mineral spirits and the thinners that you need to use for these paints actually are less dangerous to the environment in terms of creating smog and so on. And so what has happened is a lot of paint manufacturers in recent years have started replacing some of the more synthetic type varnishes with this type of finish, and so we’re seeing them more and more appearing in wood stains and deck stains and even some kinds of paint.

The problem is a fairly simple one and that is that natural vegetable materials have a tendency to decompose, and they do so, and usually it’s quite a harmless process. I mean, it’s just composting vegetation, this sort of thing, the way that things naturally break up, but under some circumstances, and it’s especially visible in these kinds of spontaneous ignition fires, what you have is these vegetable oils, instead of just slowly releasing the heat in the normal way, when you add them to a cotton rag, what they can do is they can react a great deal faster, and so the process is accelerated. The other factor that comes into play is that the rags themselves are very good thermal insulators, and so if you wipe these stains with these rags and then you simply bundle the rags up after use and put them in something like a cardboard box, what will happen is the heat will build up inside the rags and actually cause them to catch fire from the inside. It’s indeed a smoldering combustion typically, rather than a flaming combustion, and so it builds up a great deal of heat, and that heat is capable of simply setting the material on fire on its own. So, of course, you don’t need a match or something else to set alight, and in this way these materials can be a very serious hazard because they’re a very strong ignition source in the sense that they get very hot for quite a long time. So they can set fire to your surrounding combustibles and set them aflame, and of course, that’s when you have these house fires that you were talking, in fact, you were saying earlier about one that had been reported in England recently and had been attributed to this sort of thing.

INTERVIEWER: What evidence can be left behind that a fire investigator should recognize?

DAVID HOWITT: There’s a couple of little things that the first investigator should be aware of, and it’s an odd effect, and I studied it a little bit myself just with some laboratory experiments, and that is that the process that gives rise to the heating, the chemical reactions actually tend to occur right around room temperature. It’s somewhere about 20 degrees centigrade is the cutoff value. So we’re talking about something close to about 70 degrees, 72 degrees Fahrenheit. When the temperature is fairly low and you mix these rags or you do the staining at these kind of temperatures, you often don’t have a problem. It’s when the temperature gets just a few degrees higher than that and that’s when the reaction can start and it essentially is a bit like a snowball reaction. And so the temperatures are quite important in determining certainly for the first investigator whether or not it’s a likely occurrence.

The other thing, of course, that’s important is determining exactly what kind of oils were in the paint because it’s only vegetable oils that do this thing. The petroleum base and the synthetic oils don’t actually do this. So, for example, you couldn’t get this effect with soaking, for example, motor oil in rags, it wouldn’t heat up at all. It’s just the vegetable oils. But it’s very much a hit and miss process. If the temperature is 23, 24 degrees centigrade, then it becomes much, much more likely that you’re going to get a reaction than if you were at 21 or 20 degrees. Just those few degrees difference, and that’s what made the determination of this effect a little bit of a mystery for people because when you do the experiments, if you’re not very careful with the temperatures, you can have it not happen or you can have it happen. The big thing is that the ignition source is very strong, and so you’re often, if, for example, a cardboard box was left on a wooden floor, you might expect actually the wooden floor to be burned through locally. You would expect to find deep burn marks where the reaction occurred. That will be the first thing.

Unfortunately for the fire investigator the spontaneous ignition process is so thorough that it rarely leaves any evidence behind, but it does need something known as rigid char to form, and if in fact the ignition source hasn’t been disturbed in the process of the first investigation, you can often detect this rigid char simply because you’ll find, as I said, a bundle of rags that if it’s undisturbed will simply fall apart when you touch it. This rigid char is necessary because it’s the thing that controls the flow of air to the interior of the rags, and in doing so it enables the reaction to occur. If you lay these rags out flat or if you hang them on a washing line, for example, they won’t heat up simply because the heat is able to escape into the air, and if you have a rapid air flow through the rag pile the same sort of thing will happen. So the rigid char itself, when it forms, allows the air to get slowly into the interior of the pile and that’s what essentially stimulates the reaction, and you can often see that in the remnants simply because obviously you’ve had a burning on an interior and not the exterior and the remnants left can sometimes clue you in.

There are also chemical tests you can do on the residues that you find because most of these paints and stains contain, they’re actually methyl soaps. Soaps typically of zirconium and manganese and those elements are fairly readily detectable by simply doing an ICP type analysis. And so if you have some of the residues from what you think is a spontaneous condition, you can actually do chemical tests to determine the presence of, they’re actually referred to as metallic dryers because they’re not indigenous, typically you won’t find them elsewhere, and so if you find things like cobalt or manganese or zirconium present, then that’s a clue that you may have had this sort of activity going on. People sometimes try and do tests for the oils themselves, but those are typically not very successful because the oils invariable decompose and they’re also very difficult to spot.

INTERVIEWER: What questions should a fire investigator ask witnesses to determine if spontaneous combustion of this type might have been the cause of the fire?

DAVID HOWITT: What you typically see with these kinds of ignitions is that it takes typically four to six hours for the ignition source itself to heat up to a sufficient temperature. And then it can often take an hour or so after that before it actually bursts into flame, and so this period of six to eight hours is usually the time that you can expect from the moment essentially that the rags are bundled up into a pile, to the time that the fire is actually reported. So if the first investigator can get, certainly from whoever was doing painting or staining, a fairly good description of what they did, when they finished their work, the circumstances and so on, even whether it felt warm, whether it was cool, whether they were doing it inside or outside, this sort of thing, and then follow through that scenario and see if they can pinpoint the time at which they think the rags would have begun to self-heat. And then as I said, typically you can predict that six to eight hours after that you should have had the fire reported.

It’s also, of course, important to know what the people were doing in terms of how they were applying the stain because another thing that’s actually a common misconception with these sorts of fires is that it’s not actually a rag that’s sodden in stain that is the danger, it’s the one that only has a small amount of stain in it. In fact, the optimum mixture is about the same weight of rag as it is to stain, and when you have that situation, the rags actually feel fairly dry. And so, there’s, of course, the temptation to keep those rags because you could, you know, feasibly use them again if they dried out a little bit, and those are the rags that are the most dangerous and the most likely to spontaneously ignite. So, yes, a detailed description of what exactly went on, what happened and the timing can be very useful in predicting whether actually such an ignition was likely.

INTERVIEWER: Thanks again David. We appreciate your expertise. Now, let’s turn our attention to two current news stories.

A recent AP article examined another side of the rise in vacant home fires. In previous podcasts, we’ve talked about the incentive for property owners affected by the recession to set fire to their buildings for insurance settlements and how this has contributed to the rise in arson for profit. However, there is another side to the rise in vacant building fires: accidental fires resulting from the actions of squatters living in vacant, abandoned, or foreclosed and bank-owned homes.

According to the Census Bureau, a staggering 19 million homes now stand vacant, many as a result of the foreclosure crisis and economic downturn. People who have lost their own homes are seeking refuge in vacant houses, which usually have no electricity or cooking and heating fuel. Therefore, the squatters engage in unsafe cooking, heating, and electricity procurement practices. These unsafe practices raise the risk of accidental fire.

The Associated Press profiled one community, in Flint, MI, where this reality turned into tragedy. In Flint, more than 1,000 homes sit abandoned, awaiting demolition. One of those homes was 1430 Jane Avenue. The home was abandoned by the owner and in tax foreclosure. But, it wasn’t unoccupied. Gordon Yoesting, a well-known and well-liked local who had grown up on Jane Avenue, returned to his old neighborhood having survived a vicious criminal beating. But he was never the same. He got by on itinerant jobs and disability, living in cheap apartments. Until he got an idea about 1430 Jane Avenue. Yoesting asked the owner, who had given up on the property as it went through the tax foreclosure process, if he could take care of the place. The owner gave him a set of keys. Yoesting set about tidying the mess and rigging up a way to get water and electricity. Yoesting told neighbors that he was going to buy the place; the local Land Bank who controlled the property told him he was being evicted. Shortly thereafter, tipped off by someone, the electric company shut off the illegal service. A few days later, Yoesting had lit some candles for light as he worked on a lawn mower in the living room. How the fire actually started isn’t clear, but by the next morning, the house was ablaze and Gordon Yoesting was dead inside. All fire investigators should be aware to possibilities like squatters when investigating abandoned building fires and alert for evidence of human habitation.

Illegal occupants aren’t the only victims of these vacant building fires. Firefighters, who are taught to attack fire vigorously, are also in increased danger. After a Detroit firefighter was killed when fighting an intentional fire in an abandoned home, the city began to look differently at these abandoned building fires. More municipalities followed suit, implementing new policies to safeguard firefighters — if the building is vacant and no one appears to be inside, fire companies are instructed to attack the fire only from the exterior. This new approach has ramifications for evidence survival, and thus investigative outcomes. In addition, the new policies decrease the chance of finding victims that no one knew were inside.

Our second news item is an alert about research underway in Australia to examine what happened in the "Black Saturday" brushfires that ravaged the state of Victoria in February 2009. As reported by ABCNews in Australia, one aspect of this research looks at human behavior during the fires. Preliminary, anecdotal findings in Marysville indicate that half of the people who died in their homes were found sheltering in a bathroom, even though bathrooms are not advised as sheltering places because they typically have no windows. The full report is due in mid-August.

Finally, we close with news from IAAI. Following up on our previous vacant buildings story, IAAI offers an Abandoned Building Project Tool Box that assists public officials in dealing with vacant and abandoned buildings, ensuring the safety of fire suppression personnel who respond to vacant and abandoned building fires, and reducing the incidence of incendiary fires involving these properties. The package can be purchased by contacting the IAAI office at 1-800-468-4224.

That concludes this IAAI CFITrainer.Net podcast. We’ll see you again next month.