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How to tell if something is flammable



NFPA signs help protect workers by indicating risks like the flammability, potential health hazards and reactivity of a chemical. They can also list what personal protective equipment is necessary for safely handling the substance.

If you’re wondering if a substance is flammable, it’s probably not a good idea to light a match and see. Most of the time, especially with chemicals, there are signs and cautionary indicators in place to let you know if something is flammable. They might even contain the word “flammable” in big letters. (Confusingly, the word in some places is “inflammable,” but they mean the same thing.)

To better understand flammability measures, it’s important to understand that even flammability has a bit of its own jargon. A flash point is the temperature at which a substance will start to vaporize to form a combustible gas. Liquids like gasoline have extremely low flash points, meaning that the air above the liquid is flammable even at very cold temperatures. This is why gasoline is kept in a closed container at almost all times. An auto-ignition temperature is the temperature at which a substance will ignite without a spark. The flammability of a material is determined by its flash point.

The red diamond on the NFPA’s Code 704 Diamond Label, for example, uses flash points as its main determinant of flammability. Commonly referred to as the “fire diamond,” the diamond label is made up of four differently colored quadrants. At the twelve o’clock position, the red quadrant indicates the substance’s flammability on a scale of 0 to 4. Substances marked with a 0 are not at all flammable, like water. Substances marked with a 4 will burn readily due to their extremely low flash points, like propane or hydrogen. The fire diamond is usually used on drums or barrels of the substances themselves, not on their means of transport.

For transportation purposes, the U.S. Department of Transportation (DOT) uses hazmat placards for hazardous substances. There are nine classes of hazmat labels, and a third of them indicate a substance’s flammability. Classes 2, 3, and 4 mark flammable gases, liquids and solids, respectively, and each have their own placards to mark the back of trucks transporting them.

Finding out if a substance is flammable isn’t too difficult. Usually it will be indicated by a diamond on the container. If not, you can always consult a chemical’s Material Safety Data Sheet (MSDS), which are mandatory when working with chemicals, to check on its flammability and see if there are any other warnings in place for safety around the chemical.

In this table, nine flammable household substances are listed, along with their flash points and autoignition temperatures.
 

Chemical name

Flash point (°C)

Flash point (°F)

Autoignition temperature (°C)

Autoignition temperature (°F)

Description

Acetone

18

0

465

869

Found in nail polish remover and paint thinner.

Benzene

-11

12

560

1040

Used plastic, rubber and paint production.

Ethanol

12.78

55

365

689

Often sold as rubbing alcohol and vehicle fuel. Also the alcohol in alcoholic beverages.

Gasoline

-43

-45

280

536

Makes your car go.

Naphthalene

79

174

550

1022

Found in mothballs and moth crystals.

Propane

-104

-156

470

878

Used as fuel for engines, grills, and houses.

Styrene

31

88

490

914

Found in cement, wood sealer, and caulk.

Toluene

4

40

535

995

Used as a solvent in products like paint.

Xylene

17

63

463

867

Found in spray paints and adhesives.

 
 
 
 
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