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...


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.

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