Cause of Fire: Spontaneous Combustion
Some fires are just plain weird. They have weird circumstances, weird sources, weird ignition factors and weird paths of travels. Spontaneous combustion fires fall into this category.
Spontaneous combustion is an exothermic chemical reaction when chemical compounds mix and generate their own heat. As the temperature increases and vapors are being released, they reach their ignition temperature. With the right mixture of oxygen, rapid oxidation takes place and you have a fire. The key factors that need to exist for this type of fire to occur are a confined space for the heat and vapors to accumulate and sufficient oxygen to complete the fire triangle (or tetrahedron). Any type of ventilation with airflow would allow the vapors and heat to dissipate. This is why many spontaneous combustion fires occur in containers with loose-fitting lids and in enclosed storage closets.
Now, I have heard of spontaneous human combustion, but that’s too weird for me. I find it hard to believe and have never experienced an actual case, but perhaps it’s true. This fire story, however, is about a spontaneous combustion incident that is true.
This fire happened to one of my neighbors, whom I will call “Sam.” Sam recently remodeled his kitchen and had a subcontractor lay a new hardwood floor. This subcontractor used a 4’x 8’ sheet of plywood as a cutting surface and also used it for a wood-staining surface. After the job was completed, Sam stored the sheet of plywood under his deck in an enclosed area. This area under the deck is also part of the cellar, which has an access door that was always kept closed to keep animals out. Within a few days, the fire started.
The night of the fire, Sam remembered smelling a burning odor that he wrote off as someone barbecuing hotdogs. Perhaps midnight barbecues are a normal event on his street, but on my street, any burning odor at midnight would be checked out. At approximately 03:30 hours, a stronger odor of smoke woke up Sam and his family. (No smoke detectors). He said to his wife, “Quick! Call Raul!” (Have you ever noticed how neighbors and family members will call you first in an emergency before calling 911?). His wife got the kids out of the house and called East Pierce Fire and Rescue while Sam went downstairs to investigate.
He encountered visible smoke in the kitchen and pantry. Smoke was coming up through the vents and from around the base of the furnace. It’s remarkable that Sam figured out the fire had to be coming from below; most civilians would be in a panic at this point and run for possessions or run out of the house.
Sam went out back and opened the access door below the deck and discovered the seat of the fire with visible smoke and flames. Armed with only a garden hose and pajama bottoms as protective clothing, he successfully extinguished the fire.
The proud feeling that comes with protecting your home single-handedly from the ravages of fire and accomplishing this feat while half-naked, well, it would be difficult for any man to contain himself. Sam was so proud of himself, and he couldn’t wait to tell me about his brave new adventure — especially how he had the fire out before the first arriving fire unit. Every time he tells the story, we have to strike another alarm! Here’s a photo of Sam re-enacting his initial interior attack on the fire (photo 1). He is now an honorary member of Engine Company 33.
Photo 1
Well, we had some fun with Sam; but let’s take a closer and more serious look at what went on here for future reference. These lessons learned can be applied to the job as well as our own private residences.
First, the family did not take the initial odor of smoke seriously enough to check it out. Perhaps Sam would have been able to discover the fire prior to ignition. We, as firefighters are sometimes too quick to dismiss odors we can’t locate. Odor is one of the early clues that there is a fire. We need to take odors seriously and have the patience to trace them to a source.
Second, there were no smoke detectors in the home. The family was lucky to be awakened by the odor of smoke. Other families, as we know, are not so lucky. How many smoke detectors do you have in your home? I have four. One is hard-wired and the others are battery-powered. Sam has since outfitted his home with numerous smoke detectors and a couple of fire extinguishers.
This next photo shows the access door to the cellar area (photo 2). Cellar areas like this are excellent places for homeowners to store things they don’t know what to do with. Out of sight, out of mind. All types of combustibles and flammable liquids can be found there. When hazard items are not stored properly, they can be a recipe for fire. The fire takes the path of least resistance and in cellars and basements, it usually fans out, then spreads up.
Photo 2
Photo 3 is of the sheet of plywood that was later removed by firefighters. It was inside the cellar, leaning up against the exterior wall of the house on side C. Notice the classic V-shaped burn pattern. A closer look at the plywood reveals the sheen of the saturated wood caused from excess spillage of the wood stain product (photo 4).
Photo 3 |
 Photo 4 |
The “V” pattern on the interior of the exterior wall on side C matches that of the plywood. What’s key here (and it’s hard to tell from this photo, photo 5) is that there is no ignition source. There was no indication that this fire was deliberately set, and there are no electrical wires or appliances that would act as a source of heat. So it had to be spontaneous combustion based on the information of the recent kitchen remodel. Notice the burn pattern traveling along the heating vent. Unless there is absolute integrity in this ductwork, smoke can enter the duct and spread throughout the house.
Photo 5
Finally, notice the amount of charring present on the underside of the floor joists and studs along the exterior wall (photo 6). It is fairly substantial. This content fire progressed into a structure fire. Had this been lightweight construction with gusset plates / gang nails instead of full dimensional lumber; a portion of the floor could be weak enough for structural failure or partial collapse. Remember, structural failure has occurred in lightweight construction in as early as 2-5 minutes — certainly within the time frame that firefighters would be making entry into this type of fire.
Photo 6
In closing, you can see how a series of harmless events can have the potential for disastrous consequences. So:
Take personal inventory of your own home. Can this story happen to you?
Don’t save oily rags, cardboard or materials that have been used with or can absorb flammable or toxic home maintenance products. Get rid of them!
Share stories like this at community and school events when your fire department is asked to speak about fire prevention.
Write stories like this in community newspapers or neighborhood newsletters. People relate to true stories.
When investigating odors of smoke incidents, odors that present themselves on upper floors can originate in the lowest level of the occupancy.
Smoke and odors of smoke can travel through HVAC ductwork and make the source difficult to trace. Be patient. Be persistent.
Be aware that fires in basements and cellars can be fueled by anything, and they will travel out and up.
Always suspect lightweight construction on newer homes, and realize you do not have a lot of time once it changes from a contents fire to a structure fire.
During the initial fire investigation to determine a cause, suspect the possibility of spontaneous combustion if the circumstances support this assumption and there is no other logical source of ignition.
Follow the criteria of your department policy in calling for the fire investigation unit.
Stay safe.
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