Flammable Substances

Fire Chief

Stan Sharp
[email protected]
(865) 595-4480

Public Safety Complex
1630 Huron St., Bldg. C
Knoxville, TN 37917

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Flammable and combustible products are used for a wide variety of purposes and are commonly found in the home. Gasoline is the most common, but there are other flammable and combustible liquids and gases used in the home including: 
  • paint solvents 
  • lighter fluid 
  • dry cleaning agents 
  • butane 
  • pesticides 
  • oil 
  • spray paint 
  • kerosene 
  • propane 
  • diesel fuel 
  • turpentine 
  • nail polish

Many households use natural gas, propane or fuel oil heating. Each product poses a serious health or fire danger if not used and stored properly.

Background Information

A flammable liquid in its liquid state will not burn. It only will ignite when it vaporizes into a gaseous state. All flammable liquids give off vapors that can ignite and burn when an ignition source such as a lighted cigarette or spark is present.

To understand the dangers associated with flammable liquids, it is useful to be familiar with the terms used to describe their chemical properties. They are:
  • Flash point
  • Flammable/combustible liquids
  • Flammable range
  • Ignition temperatures
  • Vapor density

Flash point - The temperature at which a particular flammable liquid gives off vapors (vaporizes) and therefore can ignite. The flash point differs for each type of flammable liquid. Kerosene has a flash point of 110 degrees Fahrenheit. Gasoline has a flash point of -40 degrees. This means that at 110 degrees or higher kerosene gives off flammable vapors and can ignite. However, gasoline requires a temperature of only 40 degrees to vaporize to cause an explosion or fire. This means that when the temperature is freezing, gasoline still vaporizes and can cause an explosion and/or fire. At the same temperature, kerosene cannot ignite. Liquids such as gasoline with a flashpoint below 100 degrees are called flammable liquids. Kerosene and other liquids with a flash point above 100 degrees are referred to as combustible liquids.

Flammable range refers to the percentage of a flammable liquid, in its gaseous state, to air to create an explosive mixture. This varies with different flammable liquids. Gasoline has a flammability range of 1.4 to 7.6 percent. This means it will ignite when there is 1.4 parts of gasoline mixed with 100 parts air. With this in mind, 1.4 percent is known as the lower flammable limit and 7.6 percent is the upper flammable limit of the flammable range. A product mixed with air below the low end of its flammable range is too lean to burn. A flammable liquid which exceeds its upper flammable limit is too rich to ignite. Ethylene oxide is extremely flammable. It has a flammable range of 3.6 to 100 percent. This means it can burn even if there is no air.

Gasoline has a narrow flammable range and is metered precisely in a vehicle's carburetor to obtain the desired flammable range. A vehicle will have trouble operating if the carburetor meters too much gasoline. This is referred to as a rich mixture, which is too concentrated for ignition by the spark plugs. Too little gasoline in a vehicle's carburetor is called a lean mixture, which is too diluted for ignition.

The ignition temperature is the temperature required for a liquid to continue to emit vapors which can and sustain combustion. Gasoline will ignite when a heat source or electrical spark of at least 853 degrees comes in contact with it. Natural gas (methane) needs an ignition temperature of around 1000 degrees and paint thinner 453 degrees.

Vapor density is the weight of a vapor relative to the weight of air. The vapor density of natural gas causes it to be lighter than air and will rise when exposed in the open. The vapor density of gasoline is heavier than air and will seek low points when it is exposed to the air. Products with a high vapor density (heavier than air) behave much like carbon dioxide gas escaping from a block of dry ice. (Dry ice is frozen carbon dioxide gas.) A term used in the fire service is BLEVE. It is an acronym for "Boiling Liquid Expanding Vapor Explosion." A BLEVE occurs when a confined liquid is heated above its atmospheric boiling point. The vapors expand and suddenly the container will explode. 

Gasoline and Other Flammable Liquids and Gases

Never smoke around gasoline or other flammable liquids. Do not use it as a cleaning solvent or to remove grease and oil from automotive parts, your hands or clothing. Many people are seriously burned each year from these mistakes. Do not pour gasoline or other flammable liquids down the sink or into a storm drain. This creates an explosion potential.

Do not store gasoline in the house. It should be kept in a detached garage or in an outside storage area. Be absolutely sure it is clear from any ignition source such as a water heater, washer or dryer. Do not put gasoline in a cup, glass jug or old bleach bottle. It should be stored in an approved container, which is of heavy duty construction, has a spring-loaded, self-closing handle and is equipped with a safety-relief plug.

The city of Knoxville Fire Code allows a maximum of 10 gallons of flammable liquid to be stored on residential property and the liquid must be stored outside. Storage of flammable liquids above these amounts on any property, commercial or residential, requires a permit from the Knoxville Fire Department Division of Fire Prevention.

Don't store gasoline in the trunk or back of the car. If you need to carry fuel, make sure the cap is tightly closed, and fill the can only three-fourths full, leaving an air space for vapor expansion.

Kerosene - Kerosene heaters are commonly used in many homes and businesses during colder months of the year to provide warmth. Kerosene is not as flammable as gasoline but just as dangerous. Fill a kerosene heater outdoors using a fill spout. Never fill a heating unit while hot and be sure the area is ventilated. Kerosene should be stored away from the home and any heat or ignition sources. It should be stored in an approved container like gasoline.

Other flammable liquids and gases - For health and safety reasons, paint should be used in a ventilated area. It should be stored in a secured can when not being used. Spray paint and paint solvents such as lacquer thinner, and paint brush cleaner are highly flammable and should be stored away from heat or ignition sources. Other cleaners such as naphtha and toluene can be ignited by static electricity from one's clothing. These products should be stored in secured containers away from the home in a detached storage area.

You may have a good reason to have benzine in the house - as a dry cleaning fluid or as a fluid for your cigarette lighter. Even then, you should keep the smallest quantity possible on hand...in a tightly stoppered container...stored securely away in a cool place. Benzene (with an "e"), otherwise known as benzol, is a very serious fire and health hazard (a known carcinogen). Do not use or store it under any circumstances.

Denatured alcohol may be required for some uses in the home, perhaps as a rubbing solution. While it is not quite as dangerous as some of the others, it is nonetheless highly flammable and should be used and stored with as much caution as any other flammable liquid.

Many pesticides are not only poisonous, but are highly flammable. When using pesticides, be sure you are away from any heat or ignition source. Always keep pesticides in their original containers.

Rags which have been used to wipe or clean petroleum products may spontaneously ignite. Cleaning rags soaked in oil, furniture polish, turpentine, or paint should be kept in a tightly-sealed metal container or thrown away immediately after use. 

Survival Actions Regarding Flammable Liquids

Even if you have a small spill involving a flammable liquid, immediately open your windows to ventilate the area. Do not use fans or other electrical devices, which might provide an ignition source and cause an explosion. If you get some of the liquid on your skin, remove the affected clothing and wash your skin with soap and water. Soak your clothes in water before washing them. If a large spill occurs, evacuate the area immediately and call 9-1-1.

A small fire involving a flammable liquid can be controlled with a class B fire extinguisher. Never try to extinguish a flammable liquid fire with water. This could cause the fire to spread. Do not try to control a fire involving compressed gases such as butane or propane. They are extremely dangerous. For a large fire involving a flammable liquid, evacuate the area and call 9-1-1.