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The Street Chemist - Part 25

Animal and vegetable oils, which are generally considered combustible liquids have a hidden hazard.

Previous installments of the Street Chemist have dealt with the physical and chemical characteristics of flammable and combustible liquids. Animal and vegetable oils are considered combustible liquids. The animal and vegetable oils are large, long-chained hydrocarbon compounds that are loaded with carbon & hydrogen. They are members of the alkene hydrocarbon family.

We encounter them most often in cooking operations at restaurants and food processing plants and in grocery stores in small containers. They are however, shipped in tanker truck and rail car quantities as well. With the continued development of alternative fuels animal/vegetables oils both virgin and recycled are being used to make Bio-Diesel fuels which will increase the instances in which they are encountered by emergency responders.

Bio-Diesel fuels are a cleaner burning and renewable fuel source used to supplement or replace petroleum diesel fuel. Tests have shown that Bio-Diesel reduces net carbon dioxide emissions by 78% compared to petroleum diesel. Thus Bio-Diesel does not harm the earth's ozone layer as much as petroleum diesel. Bio-Diesel will burn in most diesel engines without any modification to the engine. The original diesel engine developed in 1893 was actually designed to run on peanut oil. Bio-Diesel has a higher flash point than petroleum diesel making it safer in terms of combustibility. Pure bio-diesel is considered non-toxic as well.

animal/vegetables oils which are generally considered combustible liquids, have a hidden hazard; they may ignite spontaneously when in contact with combustible materials where heat is trapped within the material. animal/vegetables oils have high boiling and flash points, narrow flammable ranges, low ignition temperatures, and are non-polar. Examples of these liquids are linseed oil, cottonseed oil, corn oil, soybean oil, lard, butter and margarine.

These unsaturated hydrocarbon materials can be dangerous when rags and other combustible materials containing residue are not properly disposed of or when they come in contact with other combustible materials. Unsaturated hydrocarbon compounds have a characteristic double-bond in their chemical structure between two carbon atoms that reacts with oxygen in the air. While double bonds between carbon atoms are typically represented by two dashed lines one on top of the other, they are actually arched above and below the carbon atoms where it is easy for the oxygen in the air to attack the bonds.

This reaction causes the breakage of the double bond, which produces heat. If the heat is allowed to build up in a pile of rags for example, spontaneous combustion, which is characteristically slow, will occur over a period of hours. Petroleum-based diesel fuel will not undergo spontaneous combustion when in contact with combustible materials such as shop rags. That is because there are no double bonds to react with oxygen in the air and break.

Bio-diesel fuel on the other hand is made from animal/vegetables oils and will undergo spontaneous combustion when in contact with rags or other combustible materials in a form where heat can build up. Firefighters, fire prevention personnel and fire investigators need to be aware of the potential for spontaneous combustion from these oils and bio-diesel fuels.

In Verdigris, OK, a fire occurred in an aircraft hangar at a small airport. The owner's living quarters were on the second level of the hangar. Workers had been polishing wooden parts on an airplane in the afternoon. The rags used to apply linseed oil were placed in a plastic container in a storage room in the hangar, just below the living quarters.

Around 2 a.m., the rags with the linseed oil spontaneously ignited and the fire traveled up the wall into the living quarters. Fortunately the owner had smoke detectors; the family was awakened and the fire department was called promptly. The fire was quickly extinguished with a minimum amount of damage. The V-pattern on the wall led right back to the box where the linseed oil-soaked rags had been placed. There was little doubt what had happened; the confinement of the pile allowed the heat to build up as the double bonds were broken in the linseed oil, which combined with oxygen in the air and spontaneous combustion occurred.

A fire occurred on February 23, 1991 on the 22nd floor of the 30 story One Meridian Plaza high-rise building in Philadelphia and burned for 19 hours. The 12-alarm fire was fought with 51 engine companies, 15 ladder companies and 11 speciald units with over 300 firefighters at the scene.

It was the largest high-rise office building fire in modern American history - it completely consuming eight floors of the building - and was controlled only when it reached a floor that was protected by automatic sprinklers. Unfortunately the fire resulted in the deaths of three firefighters and injuries to 24 others.

The fire was started by spontaneous combustion in linseed oil soaked rags that were improperly disposed of after use. PCB contamination from the fire made the building uninhabitable and is currently being torn down. Had the contractor refinishing paneling on the 22nd floor not carelessly left oil-soaked cleaning rags unattended and unprotected in a vacant office, this fire would not have occurred. The danger of spontaneous heating of linseed oil-soaked rag waste is widely recognized.

On May 19, 2006 a fire in a Jacksonville, FL, sports bar was caused by spontaneous combustion of grill rags that had just been laundered and piled together on a storage shelf in a back room off the kitchen. Laundering of grease laden rags does not remove all of the grease from the rags. Remaining grease heated up by the heat from drying them accelerates the breakage of bonds which causes them to spontaneously combust. As the layers of rags were pealed apart, each contained brown patterns from the internal heat created within the rag pile by spontaneous combustion of the animal & vegetable grease still in the rags.

Ordinary petroleum products, such as motor oil, grease, diesel fuel, and gasoline, to name a few, do not have a double bond in their chemical make-up, they are considered saturated (there is no place for oxygen to attack the structure and break bonds that create heat). They are members of the alkane hydrocarbon family. These materials do not undergo spontaneous combustion!

This fact may come as a surprise to some people because the author knows there have been numerous fires blamed on soiled rags with those products on them. The fact is that those types of flammable liquids do not spontaneously ignite and cannot start to burn without some other ignition source. animal/vegetables oils, on the other hand, will undergo slow spontaneous combustion resulting on fires that may appear to have no natural cause and be determined as suspicious. Careful evaluation of the circumstances surrounding the fire must take place so that the proper determination of cause can take place.

Each model fire prevention code requires precautions to prevent ignition of materials such as animal/vegetables oils. Rags used with these matrials should be removed from buildings as soon as possible after use and properly disposed of. At a minimum, waste containing animal/vegetables oils awaiting removal from a building and proper disposal must be stored in metal containers with tight-fitting, self-closing lids. Leaving these materials unattended is an invitation to disaster. This is both an education and an enforcement problem for fire prevention officials.