Flammability is the ease with which a substance will ignite, causing fire or combustion. The degree of difficulty required to cause the combustion of a substance is subject to quantification through fire testing. Internationally, a variety of test protocols exist to quantify flammability. The ratings achieved are used in building codes, insurance requirements, fire codes and other regulations governing the use of building materials as well as the storage and handling of highly flammable substances inside and outside of structures and in surface and air transportation. For instance, changing an occupancy by altering the flammability of the contents requires the owner of a building to apply for a building permit to make sure that the overall fire protection design basis of the facility can take the change into account.
A fire test can be conducted to determine the degree of flammability. Test standards used to make this determination include, but are not limited to the following:
Categorisation of building materials
Materials can be tested for the degree of flammability and combustibility in accordance with DIN 4102. DIN 4102, as well as its British cousin BS476 include for testing of passive fire protection systems, as well as some if its constituent materials. The following are the categories in order of degree of combustibility as well as flammability:
- A1 (100% noncombustible = nichtbrennbar)
- A2 (~98% noncombustible = nichtbrennbar)
- B1 difficult to ignite (schwer entflammbar) Example: intumescents and some high end silicones
- B2 normal combustibility (like wood)
- B3 easily ignited (leichtentflammbar)
below are regulated in the United States
as potential workplace hazards.
- The vapour pressure is an important parameter in determining the ease of ignition. The higher the vapour pressure, the more flammable vapour is evolved from a free liquid surface at a given temperature.
Examples of flammable liquids
include, but are not limited to:
Examples of nonflammable liquids
Building codes typically apply to new construction, whereas fire codes apply to existing structures. Early Building codes
saw materials as either combustible or noncombustible. The typical combustibility tests are rather harsh, usually exposing a sample to a fire test
and then quantifying the loss of mass
afterwards. Materials that pass those tests include concrete
, etc. Over time, more building materials became available that had combustible constituents. It therefore became necessary to quantify the degree of combustibility, which roughly tracks the percentage of covalently bound
, or organic ingredients by percentage, as a general rule of thumb. There are exceptions, of course, due to the use of fire retardant ingredients, whose purpose is to reduce the flammability of the end product. With the advent of materials of "limited combustibility", codes are continuing to be refined in terms of what degree of combustibility to allow in which occupancy
. For example, in Ontario
, the Ontario Building Code differentiates between "Part 9" (of the OBC) buildings, which are combustible, such as timber frame single family homes, and "Part 3" (of the OBC) noncombustible buildings. But even within these categories, degrees of combustibility are noted for certain applications. For instance, one may use foamed plastics, even in a Part 3 building, but only if sufficiently concealed with noncombustible elements. Drywall
is an example of a limited combustibility product, as the paper burns, whereas the gypsum calcines in a fire
. Certain types of plastic pipe are permissible even in some Part 3 buildings, for instance CPVC
piping for use in fire sprinkler
applications, provided the building is not too tall and firestops
are correctly employed. ABS
piping, on the other hand, is not ordinarily allowed in Part 3 buildings because of its flammability. ABS catches on fire and spreads fire very quickly, whereas plastics with lower flammability do not pose as large a problem. With the presence of significant quantities of flammable substances, special provisions are employed to ensure that if a fire should occur, it is less likely to get out of control. An example of this is if a transformer
, which contains flammable liquids, is often located in a fire compartment
with a three hour fire-resistance rating
, whereas many other walls and floors in the same building can have lesser ratings, such as 2 hours and 1 hour.
For existing buildings, fire codes focus on maintaining the occupancies
as originally intended. In other words, if a portion of a building were designed as an apartment
, one could not suddenly load it with flammable liquids and turn it into a gas storage facility, because the fire load and smoke development in that one apartment would be so immense as to overtax the active fire protection
as well as the passive fire protection
means for the building. The handling and use of flammable substances inside a building is subject to the local fire code, which is ordinarily enforced by the local fire prevention officer.
Linguistics: Flammable vs. inflammable
The word "inflammable" came from Latin inflammāre
= "to set fire to", where the prefix in-
means "in" as in "inside" (compare English "in flames"). But there have been instances of people thinking that this "in-" prefix means "not" as in "invisible" and "incombustible" etc, and thus wrongly thinking that "inflammable" means "cannot burn". To avoid this safety hazard
, the shortened word "flammable" has come into use in recent years.
The Elements of Style ("Strunk and White") says:
- Flammable. An oddity, chiefly useful in saving lives. The common word meaning "combustible" is inflammable. But some people are thrown off by the in- and think inflammable means "not combustible." For this reason, trucks carrying gasoline or explosives are now marked FLAMMABLE.