Excerpts By Nathan Schiff, Ph.D., Schiff Consulting

Each year, hundreds of fires occur in Coin Laundromats, most of which were found to have started in dryers, but also a significant number occurred under counters or in laundry carts. These fires often occur long after the clothes has stopped in the dryer. Spontaneous Combustion can occur anywhere from coin Laundromats to huge tunnel power laundries. This article looks at the chemistry and physics of spontaneous combustion and how to prevent fires in Coin Laundromats.

How flammable is flammable?

Materials which can catch fire and burn are classified as either flammable or combustible, depending on the temperature at which they ignite. When dealing with liquids, this temperature is referred to as the flash point. The lower the flash point (the lower the temperature), the higher is the degree of flammability. For example, liquids which ignite at temperatures below 100°F, are considered to be flammable whereas those which catch fire and burn at temperatures above 100°F are combustible. For solids, such as cotton towels, rags or lint, the ignition point is referred to as the critical surface temperature.

Cotton, which is combustible, starts to decompose when the surface temperature reaches approximately 205°F and in the process, generates its own heat. For a point of reference, the normal "High Temperature" setting on a dryer is 190°F. This decaying process is accelerated when the fabric is tightly folded and placed in a confined area (like when someone over stuffs a dryer). Because it is hot, moist, and has no possible way to dissipate its heat, the oxidation continues to build upon itself, until the garment reaches the critical surface temperature and bursts into flames.

The Fire Triangle

There are three requirements necessary to support combustion as shown in the diagram:

• Oxidizing Agent - (Oxygen in the air)
• Fuel - (Clothes in the dryer)
• Heat Source - (Heat from the dryer)

In a dryer, the fuel can be garments, or more likely lint, which is easier to ignite. There are also several different types of fuel commonly found in Coin Laundries.

Cotton - By the very nature of the laundry industry, linens, especially those with a high cotton content, are combustible either as clothes, towels, uniforms, rags or lint. The ignition point for these materials is referred to as the critical surface temperature. Cotton begins to oxidize at a surface temperature of 205°F.

Oxidization is the chemical process where one material changes into another and this decaying process creates its own heat. The oxidation process continues if materials are not allowed to cool down and are placed in carts or folded and stored tightly. Because of this hot and moist environment, oxidation continues. Oxidation will continue to build on itself until the material reaches critical surface temperature and self-ignites. Then we have a fire.                                  

The oxidizing agent is oxygen, which is present in air. So where does the heating source come from hours after the dryer is turned off? To better understand the process we have understand what is meant by oxidation.