Flammability & Combustibility
IntroductionÂ
What is Flammability?
   If the material easily catches fire under normal circumstances and with the help or minimal ignition source, just a spark is sufficient. Eg: Propane.
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What is Combustibility?
   Material like wood and paper require vigorous condition to catch fire, a simple spark is not enough.
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Flammability (or) Combustibility
Ability of any substance to catch fire and burn. It catches fire easily and burn which is called flammability or combustibility. Eg: paper, kerosene, petrol, LPG.
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Non-Flammability (or) Incombustibility
Which do not catch fire is called incombustibility or non-flammability. Eg: water, sand.
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The mixture of flammable vapor and air which can catch fire in the presence of ignition source is called flammable mixture and the ability of that flammable substance/material to burn is called flammability.
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Limits of flammability
i.    Lower Flammability/Explosive Limit (LEL): [˃10%] The minimum percentage of flammable vapor in air which can catch fire in the presence of ignition source.Â
ii.      Upper Flammability/Explosive Limit (UEL): [Ë‚20%] The maximum percentage of flammable vapor in air which can catch fire in the presence of ignition source.Â
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Materials | LFL | UFL |
Hydrogen | 4 | 75 |
Gasoline | 1.4 | 7.6 |
Methane | 4.4 | 16.4 |
Acetylene | 2.5 | 100 |
Diesel | 2 | 8 (approx) |
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iii.   Lean or Weak Flammable Mixture: The concentration which are nearer to lower flammability limit are called Lean Flammable Mixture.
iv.   Rich or Strong Flammable Mixture: The concentration which are nearer to upper flammability limit is called Rich Flammable Mixture.
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Flammability Table
         All the chemical which has a flash point below 100oF is flammable and above 100oF is combustible.
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 |  | Type | FP | BP | NFPA |
 Flammable | IA | Extreme Flammable | ˂73oF | ˂100oF | 4 |
IB | Highly Flammable | ˂73oF | ˃100oF | 3 | |
IC | Flammable | Ë‚73oF-Ë‚100oF | Â | 3 | |
 Combustible | II | Extreme Combustible | ≥100oF – Ë‚140oF |  | 2 |
IIIA | High Combustible | ≥140oF – Ë‚200oF |  | 2 | |
IIIB | Combustible | ≥200oF |  | 1 |
         Where,
               FP    – Flammable Point
                            BP    – Boiling Point
                            NFPA – National Fire Protection Association
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