Quirky but Costly: How Rodents, Hoarding, and Manure Lead to Fires

A common assumption is that house fires start from obvious hazards, such as faulty wiring, unattended cooking, or heating equipment too close to combustibles. But in my work as a forensic engineer, I’ve seen that sometimes the culprits are far stranger. Rodents building nests inside HVAC units, clutter stacked floor-to-ceiling in a hoarded home, or piles of manure on hobby farms. All of these can set the stage for a fire.

These causes may seem unusual, even quirky, but the losses can be devastating. For insurers and attorneys, they’re also a reminder that fire investigations often require a deeper look beyond the obvious.

Rodent Nests: Tinder in the Machinery

One memorable case involved a high-end home that burned shortly after a new HVAC unit was put in service. At first glance, the equipment seemed to be the culprit. But after testing an exemplar through every reasonable failure mode, it became clear the odds of an intrinsic defect were extremely low.

The real problem was discovered inside the unit: a rodent nest made of twigs, grass, and insulation. Once the system energized, that debris had everything it needed to ignite—heat, fuel, and airflow. The fire spread quickly, even though the equipment itself was sound.

Rodents don’t just chew wires; they create ignition hazards where none should exist. What can appear from the outside to be improper installation or premature equipment failure often tells a different story inside the cabinet. The takeaway is simple: before assigning blame to the box, open the box—and look for what else might be in there.

Hoarding: When Clutter Fuels Catastrophe

The NFPA highlights how hoarding dramatically increases fire risks. Hoarding conditions also change how a fire behaves. Excess clutter doesn’t just add fuel; it blocks exits, hides hazards, and alters the way heat and smoke move through a structure. What might have been a small fire in an ordinary home can escalate quickly in a hoarded one.

When I arrive on scene, one of the first things I note is the overall standard of care. Has the property been reasonably maintained, or has deterioration and neglect set the stage for disaster? In hoarded homes, the answer is often obvious, and it directly affects how the fire spreads and how difficult it is to control.

For firefighters, blocked pathways and hidden hazards increase the danger of entry. For investigators, the debris makes origin and cause harder to pin down. And for everyone involved in the aftermath, the sheer fuel load complicates both safety and accountability.

Manure and Compost: Heat From Within

It might sound like a punchline, but manure piles, chicken coops, and compost heaps are well-documented fire risks. The science is straightforward: as organic matter decomposes, it produces heat. If that heat can’t escape—because the pile is too large or compacted—temperatures can rise to the point of spontaneous combustion.

I’ve walked compost yards where steam visibly rises from mulch piles on cool mornings. The same process can happen in backyard chicken coops or barns, where bedding, hay, and droppings are stored too close to heat lamps or electrical wiring. Fires in these settings aren’t just about property loss. They often involve livestock, adding a layer of emotional and financial impact.

Why these Quirks Matter

Rodents, hoarding, and decomposing organic material may sound like fringe scenarios, but they highlight an important truth: fire hazards don’t always fit the textbook examples. Unusual conditions can transform ordinary equipment or environments into unexpected hazards.

Forensic engineering is about more than confirming the obvious. It’s about digging deeper, considering the quirks, and recognizing when nature, neglect, or circumstance—not just a faulty product—played the decisive role. By approaching each scene with that mindset, we move past assumptions and get to the truth of how and why a fire occurred.

• Don’t stop at the obvious. What looks like product failure may be something entirely different.
• Scene conditions matter. The overall care (or neglect) of a property can be just as telling as a single ignition source.
• Unusual doesn’t mean unlikely. Rare causes still lead to costly fires—and demand objective analysis to sort out responsibility.

About the Author

Lucas Brown, P.E., CFEI, is a mechanical consulting engineer at EDT Forensic Engineering and Consulting. He leverages more than a decade of experience to evaluate the origin and cause of fire and explosion, and to provide consultation related to mechanical systems and machinery, HVAC systems, mechanical design, failure analysis, damage assessment, and the interpretation of codes and standards.