According to the National Fire Protection Association (NFPA), an estimated 16,800 fires occurred in 2010 that were attributed to clothes dryers and washing machines, with a vast majority of those fires involving dryers. This accounts for 4.5% of all reported home structure fires for the year (1). Investigation of dryer fires requires technical knowledge of dryer construction and operation, knowledge of fire pattern analysis, and in some cases specialized laboratory testing. This white paper will discuss some of the common causes of dryer fires, what to look for at a fire scene, and how to properly protect the evidence.
Causes of Dryer Fires
NFPA research lists the top four causes of dryer fires as:
Failure to clean
Unclassified mechanical failure
Unclassified electrical failure
Heat source too close to combustibles (2)
This information is taken from U.S. Fire Department reports. Fire departments do not employ engineers and do not have the resources to complete an in-depth investigation of all fires, so the exact percentages listed in the NFPA report may not be a true representation of the precise cause of each fire. These are likely, however, to be some of the more common causes of dryer fires.
The number one cause listed by NFPA is a failure to clean. Many homeowners are aware that their dryer vent requires periodic cleaning, but most don’t realize that the dryer cabinet itself should be opened and cleaned on a regular basis. Whirlpool (manufacturer of Whirlpool, Maytag, Amana, and other brands), GE, and Electrolux all have recommendations to open the dryer cabinet for cleaning as well as to clean the dryer vent at intervals ranging from 1-2 years, depending on the manufacturer (3,4,5).
(Figure 1: Dryer vent halfway clogged with lint.)
Dryer Vents do not need to be completely clogged with lint to cause a problem, but they do require a corresponding failure of the safety devices within a dryer to cause a fire. When the dryer vent becomes partially obstructed, it reduces the airflow through the dryer, trapping the hot, moist air inside the dryer. This raises the temperature inside the dryer and causes the thermostat to cycle more frequently.
If the thermostat fails, the temperature can increase to the high limit setting. If a self-resetting type limit switch is used, the limit switch can start to cycle frequently. A subsequent failure of the limit switch can then cause the dryer to run uncontrolled, increasing to dangerous temperatures.
Dryer vents must also be installed in accordance with applicable building codes and the manufacturer’s instructions. Long runs of vent pipe or a large number of bends can reduce the airflow through the vent and cause more lint to collect in the system. Improper vent materials can also contribute to frequent clogging of the vent or fire spread.
If the interior of the dryer cabinet is allowed to accumulate large amounts of lint, this lint build-up can act as a fuel source to start or increase the size of a fire. Lint is made up of fine individual fibers of combustible material and is easily ignited.
Various mechanical and electrical malfunctions can also cause dryer fires. A brief search of recall information at cpsc.gov can reveal several recalls of clothes dryers due to fire hazards. The model and serial number of an appliance can be used to check to see if that particular unit is part of a recall. Caution needs to be used, however, since the existence of a recall does not prove the cause of a fire, and it is also possible for units outside of a specific recall to have a failure that is related to the same cause.
Other possible causes of dryer fires include: drying of improper materials, drying rags or towels soaked with an oil that is subject to self-heating (spontaneous combustion), combustible materials placed too close to a heat source, and more.
Questions to Ask
If you are inspecting a fire scene where the dryer is suspected to have been the origin of the fire, a few helpful questions to ask of the insured are:
Have you noticed the dryer taking longer than normal to dry a load?
Have you noticed the clothes are hotter than normal at the end of a cycle?
Have you noticed that the laundry room is more humid than normal, or noticed any new water stains on drywall throughout the house?
When is the last time the dryer vent was cleaned?
When is the last time the dryer was serviced?Are records available?
Protection of Evidence and Investigation
In Amset’s experience, we have frequently found that evidence from a house fire has ended up outside the residence as a result of overhaul operations during the firefighting efforts. If a clothes dryer is suspected to have been involved in a fire and has been placed outside, steps should be taken to ensure that the evidence is protected. The dryer can be brought inside the house or tarped to protect it in-place. In either case, photograph the dryer in-place before it is moved and try to have a fire investigator on site as soon as possible.
Proper determination of the cause of a dryer fire requires technical knowledge, careful examination of all available evidence, and in some cases, laboratory testing. Amset is experienced in investigation of commercial and residential fires involving both gas and electric dryers. Our mechanical and electrical consultants are also Certified Fire and Explosion Investigators, and can handle all aspects of your fire investigation needs. We also have the ability to store evidence in our secured, heated warehouse and can host joint examinations of the evidence in-house.