Division 4.2 Spontaneously Combustible—LF/LR
DOT defines them as a pyrophoric material. These materials may be found as solids or liquids. Spontaneous combustion can occur when a hazardous material is exposed to air, such as phosphorus (Figure 3.114), or slow spontaneous combustion of animal vegetable oils or agricultural products such as hay. Spontaneously combustible materials are a concern not only to hazmat teams but to firefighters and fire investigators. These materials can start fires without any external ignition sources, and if not carefully investigated be deemed a suspicious or arson fire.
Liquids
Liquids are included in a solid category because they are spontaneously combustible. There is no other hazard class that they would fit into. Liquids can ignite without an external ignition source within 5 min after coming in contact with air.
Solids
There are other 4.2 materials that may be self-heating. That is, when in contact with air and without an energy supply (ignition source), they are liable to self-heat, which can result in a fire involving the materials or other combustible materials nearby. Bulk transport and storage may result in spontaneous combustion of agricultural products, such as hay, straw and cotton. Organic materials that are prone to spontaneous ignition at ordinary ambient temperatures must have access to atmospheric oxygen or carry oxidizer in some reactive form and be raised to its autoignition temperature by the exothermic reaction. In some cases of spontaneous combustion, moisture is essential for the resulting reaction. Hay, for example, will not spontaneously combust if the moisture level is below 33%. Some materials subject to spontaneous ignition are shown below.
Chemical Notebook
Spontaneous combustion of stored coal.
According the to the United States Department of Energy, "Spontaneous combustion has long been recognized as a fire hazard in stored coal. Spontaneous combustion fires usually begin as "hot spots" deep within the reserve of coal. The hot spots appear when coal absorbs oxygen from the air. Heat generated by the oxidation then initiated the fire."
Animal or vegetable oils such as linseed oil, cooking oil and cottonseed oil undergo spontaneous combustion when in contact with rags or other combustible materials. The oxidation reaction that occurs with animal or vegetable oils is different than the reaction with hydrocarbon petroleum-based materials. The oxygen from the air trapped in the mass reacts with the double bonds present in the animal or vegetable oils. The braking of the double bonds creates heat, which ignites the materials when they reach their respective ignition temperatures.
Petroleum products that contain saturated alkanes do not contain these double bonds and therefore cannot undergo this type of spontaneous heating and cause a fire. Fires started by this spontaneous heating process can be difficult to extinguish because they usually involve deep- seated fires. In order for enough heat to be sustained to cause combustion, there must be insulation. This insulation can be the material itself or in the form of some other combustible material such as rags or other fabrics (Hazardous Materials Chemistry for Emergency Responders).
CASE STUDIES
PHILADELPHIA, PA ONE MERIDIAN PLAZA, LINSEED OIL SOAKED RAGS
The high-rise fire at One Meridian Plaza in Philadelphia that killed three firefighters was started by rags soaked with linseed oil during construction operations and improperly disposed of (Figure 3.113).
Figure 3.113 The high-rise fire at One Meridian Plaza in Philadelphia that killed three firefighters was started by rags soaked with linseed oil during construction operations and improperly disposed of.
The rags underwent slow heating and eventually spontaneously ignited and started the fire. (Hazardous Materials Chemistry for Emergency Responders).
GETTYSBURG, PA, MARCH 23,1979 PHOSPHORUS TRUCK FIRE
An incident occurred in Gettysburg, PA, involving phosphorus being shipped under water in 55-gallon drums. One drum developed a leak and the water drained off. This allowed the phosphorus to be exposed to air, which caused it to spontaneously ignite. The fire spread to the other containers and eventually consumed the entire truck. The ensuing fire was fought with large volumes of water and in the final stages covered with wet sand. Clean-up created problems
Figure 3.114 An incident occurred in Gettysburg, PA, involving phosphorus being shipped under water in 55-gallon drums.
because as the phosphorus and sand mixture was shoveled into overpack drums, the phosphorus was again exposed to air and reignited small fires (Figure 3.114) (Firehouse Magazine).
BROWNSON, NE, 1978
A train derailment in Brownson, NE, resulted in a tank car of phosphorus overturning and the phosphorus igniting upon contact with air. Phosphorus is shipped under water so there was water inside the tank car. CHEMTREC was called and responders were told correctly that the phosphorous would not explode. However, the water inside the tank car was turned to steam from the heat of the phosphorus fire. The pressure from the steam caused a boiler-type of explosion that had nothing chemically to do with the phosphorus! This is just another example of the actors that emergency responders must be aware of when dealing with hazardous materials. Not only do the hazardous materials have to be considered, but also the container and any "inert" materials that may be involved (Firehouse Magazine).
