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May 2017 - Flammable, Combustible & Ignitable Liquid Classification According to NFPA, FM Global and DOT

The Department of Transportation (DOT), NFPA and FM Global are very different in how they classify flammable, combustible & ignitable liquids.

NFPA 30, Flammable and Combustible Liquids Code, is updated on a three year cycle with its latest revision being in 2015.

FM Global Data Sheet (FMGDS) 7-29, Ignitable Liquids Storage in Portable Containers was last revised in 2014. The Data Sheet can be updated on an as needed basis.

NFPA 30 defines a flammable and combustible liquid as follows:

Flammable liquids have closed-cup flash points below 100℉ and vapor pressures not exceeding 40 psia at 100℉ (thus excluding liquefied petroleum gases, liquefied natural gases and liquefied hydrogen).

Flammable liquids are referred to as Class 1 liquids, and are subdivided as follows:

Combustible liquids have closed-cup flash points at or above 100℉. They are referred to as either Class II or Class III liquids and are subdivided as follows:

The current liquid classification scheme followed by the U.S. Transportation Code and U.N. Transportation & DOT classify these products as follows:

A flammable liquid's flashpoint is the minimum temperature at which sufficient vapor is liberated to form a vapor-air mixture that will ignite and propagate a flame away from the ignition source - flash fire, not continuous combustion.

FMG DS 7-29 uses the term ignitable liquid, which is defined as any liquid that has a measurable fire point. They do not use the terms combustible liquid or flammable liquid. Also, the term flashpoint always refers to the closed-cup flashpoint unless stated otherwise. The ignitable liquids are categorized by flash point throughout FMG DS 7-29. Different protection criterion is provided based on the flash point of the liquid, container type and container size the liquid is stored in.

HAZMAT (Flammable / Combustible / Ignitable) Liquid rooms are one of the most expensive $/sq. ft. rooms in a facility. Properly identifying what should be stored in the HAZMAT Liquid room and what should be stored in the general warehouse can be most challenging.

Flashpoint is not the only trigger to identify flammable liquids. Another important liquid specification is viscosity, which is measured in centipoise (cps). If a liquid has a cps of 10,000 or greater it should be considered as a solid and can be stored in the general warehouse. To give an idea honey has a cps of 10,000. Items such as pastes and caulking, which may have a low flashpoint would be considered solids and can be stored in the general warehouse. Below is an example of some products and the cps.

Approximate Viscosities of Common Materials
(At Room Temperature 70℉)


Viscosity in Centipoise


1 cps


3 cps

SAE 10 Motor Oil

85-140 cps

SAE 20 Motor Oil

140-420 cps

SAE 30 Motor Oil

420-650 cps

SAE 40 Motor Oil

650-900 cps

Castrol Oil

1,000 cps


5,000 cps


10,000 cps


25,000 cps


50,000 cps

Peanut Butter

250,000 cps

Other items that can be considered as items to be stored in the general warehouse are kits. For example first aid kits might be all plastic and paper but contain an alcohol wipe that has a low flashpoint. The wipe has an insignificant amount of alcohol and the overall commodity should be considered a solid.

HAZMAT rooms may require containment of drainage per NFPA 30 and FMG DS 7-29. One of the main differences between the two standards is that FM treats all the ignitable liquids in the room to need containment and or drainage whereas NFPA does not require Class IIIB combustible liquids to require containment / drainage. Therefore NFPA allows Class IIIB combustible liquids to be stored in the general warehouse as long as they are properly protected in accordance with NFPA 30.

Analyzing HAZMAT commodity classifications of flammable / combustible / ignitable liquids is challenging. Once the products are correctly classified the next step is determining the proper protection per NFPA or FMG standards. Risk Logic is very experienced and can help in your commodity classification as well as the fire protection design of your HAZMAT storage room.