Spring Time Safety Tip

spontaneous combustion

Spontaneous Combustion Anyone?

Each year, there are many fires that occur from this phenomena that involve:

  • Mulch
  • Landfills
  • Silos
  • Recycling Plants
  • And more…

What causes this to occur?

As seen in this short video, the surface temperatures of this 3’ mulch pile were “apparent temperatures” of approximately 60-70 degrees Fahrenheit. Whereas when we rake back the mulch just a few inches under the surface we see “apparent temperatures” of anywhere between 110-130 Degrees Fahrenheit.

As wood decomposes, it creates heat. This heat can be sufficient enough to start a fire and in many cases it will be a smoldering fire that can go unnoticed for quite some time before suppression efforts are applied. 

Why should firefighters care about this?

Each year, many fires are caused by mulch self heating. According to the Safety Insurance website “the risk is that what starts as a small outdoor mulch fire can quickly spread to buildings. A mulch fire can be well underway before someone notices or is alerted by smoke alarms or sprinkler systems activating. In addition to this the code requires that combustible mulch shall be no closer than 18” to the exterior of combustible sided buildings such as (wood, vinyl, etc).”

Mulch that is piled too deeply (more than a few inches) can result in a fire. To prevent this, it is recommended to keep the mulch moist and keep it away from the sides of combustible exteriors (18” minimum).

With the increase of larger buildings such as the podium style construction, these fires pose a significant threat to occupants as they would spread from the outside in overwhelming or circumventing any interior fire suppression systems.

In addition to this, many large loss mulch fires are started by discarded cigarettes such as the following:

  • “The most notable mulch fire in Massachusetts occurred in May 2015 in a large Arlington apartment complex. One man died in the fire started by smoking materials discarded in a mulch bed, which spread to a car, then to the building. Thirty-six apartments and six cars were destroyed. The building had no sprinklers and the estimated dollar loss was $6.7 million.”
  • A huge mulch fire near the tiny Texas town of Helotes burned for three months before it died out in March, and authorities have said spontaneous combustion may have caused it.

To suppress these fires, water needs to be enhanced with a wetting agent/foam that breaks down the surface tension of water allowing it to penetrate deeper into these deep seated fires. With the addition of these agents, a fire can be extinguished more efficiently and quickly than standard water alone (and with less water). Please be sure to use a foam/wetting agent that is non-carcinogenic. 

As we are all approaching Spring and will be working in our yards more, please share this information with your neighbors who may not be aware that numerous home fires start each year due to spontaneous combustion from mulch. 


Thanks again for your support,

Instructor Andy Starnes

Insight Fire Training 

Level II Thermography Certified