Difference Between Flammable and Combustible (With Table)

Both flammable and combustible substances are substances that can easily catch fire. These two substances differ from each other based on the specific temperatures they must be exposed to for catching fire. Many workplaces utilize flammable and combustible liquids and to keep the workplace safe and manage the risks effectively one must understand the difference between flammable and combustible.

Flammable vs Combustible

The difference between flammable and combustible is that flammable substances are more dangerous compared to combustible substances as they can catch fire and burn easily at normal room temperature. On the other hand, combustible substances need a higher temperature to catch fire. It can catch fire and burn at temperatures that are generally higher than room temperature.

Flammable substances are the ones that are flame or ignited immediately at a high temperature or when contacting with fire and continued to slightly flame or burn when leaving the fire, like fiberboard, foil, wood, and plywood. Plants that use, store, or display flammable substances have a greater chance of experiencing hazards compared to other plants. 

Combustible substances are the substances that combust or burn in the air. In a workplace, combustible liquids and combustible dust are of particular concern. Combustible substances are more likely to catch fire in dust form as in dust form combustible substances are highly oxygenated. Some of the well-known combustible substances are acetone, butane, gasoline, propane, and natural gas.

Comparison Table Between Flammable and Combustible

Parameters of ComparisonFlammableCombustible
DefinitionFlammable substances are substances that can catch fire or ignite immediately when contacting with high temperature or fire and continue to slightly flame when leaving the fire, like wood, fireboard.
             
Combustible substances are substances that catch fire or burn as a result of a chemical reaction or fire. 
FlashpointFlammable substances have a flashpoint of less than a hundred-degree Fahrenheit. Flammable substances are more likely to ignite or catch fire as the flashpoint is lower than the combustibles. 
             
Combustible substances have a flashpoint at or above a hundred-degree Fahrenheit. It is less likely to catch fire compared to flammable substances.
ClassificationThere are three classes of flammable liquids-I-A (ligroin, diethyl ether, pentane), I-B (benzene, ethanol, acetone, cyclohexane), I-C (p-xylene).
             
There are three classes of combustible liquids- II (motor oil, diesel fuel, cleaning solvents, kerosene), III-A (oil-based paints, mineral oil, linseed oil), III-B (neatsfoot oil, oil-based paints).
Explosion hazardFlammable substances can cause some serious fire hazards. Flammable liquids can burn easily and very fast.
             
Combustible substances can cause a serious fire hazard.
Examples Acetone, alcohols, gasoline, diethyl ether, toluene.
             
Ethanol, propane, wood, kerosene, hydrogen gas, cooking gas, methane, wax.

What is Flammable?

Flammable substances are the materials that ignite and continue to burn in the contact of fire or any source of igniting. It can exist in the liquid, gaseous, or solid state. Most of the flammable liquids are volatile. Flammable liquids release vapors that mix with the nearby air to form a flammable mixture. This flammable mixture ignites in the contact of an ignition source. 

Factors like flash point, flammability limits, and temperature of auto-ignition determine the flammability of a material. Flammable liquids are generally volatile. They evaporate and emit vapor at lower temperatures. 

Flammable liquids emit vapors that are mixed with air in proper amounts in the presence of an ignition source which can cause an explosion. The proper amount is referred to as flammable range or explosive range. The explosive or flammable range includes every concentration of flammable gas or vapor in the air, in which a flame will travel or a flash of fire will occur if the mixture is capable of catching fire.

Flammable substances shall be stored far away from stairways, exits, and public areas. It shall be stored in closed containers or tanks. Flammable liquids need to be stored in a safe place with proper fire control devices like portable fire extinguishers or small hoses. 

What is Combustible?

Combustible substances are substances that can easily burn or combust in the air in contact with any source of ignition. Paper, wood, rubber, plastics, etc. are the example of combustible substances. Combustible substances react with oxygen foe producing light and heat. Simply combustible substances burn in the air at a fixed temperature.

Combustible substances have a flashpoint at or above a hundred-degree Fahrenheit. It is less likely to catch fire compared to flammable substances. Combustible substances need three main conditions to burn or combustion– a combustible substance, a supporter substance of combustion, and reaching the ignition temperature. There are mainly three types of combustion- spontaneous combustion, rapid combustion, and explosion. 

In spontaneous combustion, combustible substances spontaneously burst into flames. In rapid combustion, combustible gases burn very quickly creating light and heat. In the explosion, the combustible substances quickly react as a reaction of the light, sound, and heat creating a huge amount of gas.

The volatility of the material is an important factor that determines the level of air’s combustibility. This is dependent on its vapor pressure and this vapor pressure is related to temperature. If the material’s surface area increases the vapor quantity also increases forming mist. For instance, a small piece of paper easily catches fire while an oak desk made of wood-like paper is harder to burn or ignite.

Main Differences Between Flammable and Combustible

  1. Flammable substances are substances that can catch fire or ignite immediately when contacting with high temperature or fire and continued to slightly flame when leaving the fire, like wood, fireboard. On the other hand, combustible substances are substances that catch fire or burn as a result of a chemical reaction or fire.
  2. Flammable substances have a flashpoint of less than a hundred-degree Fahrenheit. Flammable substances are more likely to ignited or catch fire as the flashpoint is lower than the combustibles. Combustible substances have a flashpoint at or above a hundred-degree Fahrenheit. It is less likely to catch fire compared to flammable substances.
  3. There are three classes of flammable liquids-I-A (ligroin, diethyl ether, pentane), I-B (benzene, ethanol, acetone, cyclohexane), I-C (p-xylene). There are three classes of combustible liquids- II (motor oil, diesel fuel, cleaning solvents, kerosene), III-A (oil-based paints, mineral oil, linseed oil), III-B (neatsfoot oil, oil-based paints).
  4. Flammable substances can cause some serious fire hazards. Flammable liquids can burn easily and very fast. Combustible substances can cause a serious fire hazard.
  5. Some of the flammable substances are Acetone, alcohol, gasoline, diethyl ether, toluene. Some of the combustible substances are Ethanol, propane, wood, kerosene, hydrogen gas, cooking gas, methane, wax.

Conclusion

Both flammable and combustible substances easily catch fire or burn. In general, flammable substances can catch fire at standard working temperatures, while combustible substances usually catch fire or burn above the standard working temperature. Flammable and combustible substances differ from each other based on their flashpoint.

So, the main difference between flammable and combustible is that flammable substances are more dangerous compared to combustible substances as they can catch fire and burn easily at normal room temperature. On the other hand, combustible substances need a higher temperature to catch fire. It can catch fire and burn at temperatures that are generally higher than room temperature.

Refferences

  1. https://books.google.co.in/books?hl=en&lr=&id=VCCHeNV8BtYC&oi=fnd&pg=PP10&dq=what+is+flammable+&ots=GraLR3jjuL&sig=fni_xHlqYM6534dcBmxeTpk7KEY&redir_esc=y#v=onepage&q=what%20is%20flammable&f=false
  2. https://onlinelibrary.wiley.com/doi/abs/10.1002/jctb.5010020104



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