Combustibility - AbsoluteAstronomy.com

Combustibility is a measure of how easily a substance will set on fire, through fire

Fire

Fire is the rapid oxidation of a material in the chemical process of combustion, releasing heat, light, and various reaction products. Slower oxidative processes like rusting or digestion are not included by this definition....

or combustion

Combustion

Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...

. This is an important property to consider when a substance is used for construction or is being stored. Special precautions are usually required for substances that are easily combustible. These measures may include installation of fire sprinkler

Fire sprinkler

A fire sprinkler system is an active fire protection measure, consisting of a water supply system, providing adequate pressure and flowrate to a water distribution piping system, onto which fire sprinklers are connected...

s or storage remote to possible sources of ignition.

Substances with low combustibility may be selected for construction where the fire risk needs to be reduced. Fire resistant

Fire-resistance rating

A fire-resistance rating typically means the duration for which a passive fire protection system can withstand a standard fire resistance test. This can be quantified simply as a measure of time, or it may entail a host of other criteria, involving other evidence of functionality or fitness for...

substances are preferred for building materials and furnishings.

Code Definitions

For an Authority Having Jurisdiction, combustibility is defined by the local code. In the National Building Code of Canada

National Building Code of Canada

The National Building Code of Canada is the model building code of Canada. It is issued by the Institute for Research In Construction ], a part of the National Research Council of Canada...

, it is defined as follows:

Combustible: A material which fails to meet acceptance criteria of CAN/ULC-S114, Standard Method of Test for Determination of Noncombustibility in Building Materials.

This leads to the definition of Noncombustible:

Non-combustible: means that a material meets the acceptance criteria of CAN4-S114, "Standard Method of Test for Determination of Non-Combustibility in Building Materials".

Fire testing

Various countries have tests

Fire test

A fire test is a means of determining whether or not fire protection products meet minimum performance criteria as set out in a building code or other applicable legislation. Successful tests in laboratories holding national accreditation for testing and certification result in the issuance of a...

for determining noncombustibility of materials. Most involve the heating of a specified quantity of the test specimen for a set duration. Usually, the material cannot support combustion and must not undergo a certain loss of mass. As a rule of thumb, concrete, steel, ceramics, in other words inorganic substances pass these tests, which permits them to be mentioned in building codes as being suitable and sometimes even mandated for use in certain applications. In Canada

Canada

Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

, for instance, firewalls

Firewall (construction)

A firewall is a fireproof barrier used to prevent the spread of fire between or through buildings, structures, electrical substation transformers, or within an aircraft or vehicle.- Applications :...

must be made of concrete

Concrete

Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

Relevance in construction

In building construction

Construction

In the fields of architecture and civil engineering, construction is a process that consists of the building or assembling of infrastructure. Far from being a single activity, large scale construction is a feat of human multitasking...

, buildings are typically divided into combustible and noncombustible ones. The code provisions and safety measures that must be taken into account in the design and construction of a building depend to a significant extent upon whether the structure is made from noncombustible elements, such as concrete

Concrete

, brick

Brick

A brick is a block of ceramic material used in masonry construction, usually laid using various kinds of mortar. It has been regarded as one of the longest lasting and strongest building materials used throughout history.-History:...

and structural steel

Structural steel

Structural steel is steel construction material, a profile, formed with a specific shape or cross section and certain standards of chemical composition and mechanical properties...

, or a combustible element such as wood

Wood

Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...

. Combustible structures have more stringent limits on maximum building height and area.

Related matters

The flammability

Flammability

Flammability is defined as how easily something will burn or ignite, causing fire or combustion. The degree of difficulty required to cause the combustion of a substance is quantified through fire testing. Internationally, a variety of test protocols exist to quantify flammability...

article describes further the subcategorisations of combustible matters. Here, further fire tests are involved in quantifying the degree of flammability or combustibility.

The chemistry underlying the fire testing and resulting code classifications

The degree of flammability

Flammability

or combustibility depends largely upon the chemical composition of the subject material, as well as the ratio of mass versus surface area. As an example, paper is made from wood. A piece of paper catches on fire quite easily, whereas a heavy oak desk is much harder to ignite, although the wood fibre is the same in each substance, be it a piece of paper or a wooden board. Also, Antoine Lavoisier

Antoine Lavoisier

Antoine-Laurent de Lavoisier , the "father of modern chemistry", was a French nobleman prominent in the histories of chemistry and biology...

's law of conservation of mass

Conservation of mass

The law of conservation of mass, also known as the principle of mass/matter conservation, states that the mass of an isolated system will remain constant over time...

, states that matter can be neither created nor destroyed, only altered. Therefore, the combustion or burning of a substance causes a chemical change, but does not decrease the mass of the original matter. The mass of the remains (ash, water, carbon dioxide, and other gases) is the same as it was prior to the burning of the matter. Whatever is not left behind in ashes and remains, literally went up in smoke

Smoke

Smoke is a collection of airborne solid and liquid particulates and gases emitted when a material undergoes combustion or pyrolysis, together with the quantity of air that is entrained or otherwise mixed into the mass. It is commonly an unwanted by-product of fires , but may also be used for pest...

, but it all went somewhere and the atoms of which the substance consisted before the fire still exist after the fire, even though they may be present in other phases

Phase (matter)

In the physical sciences, a phase is a region of space , throughout which all physical properties of a material are essentially uniform. Examples of physical properties include density, index of refraction, and chemical composition...

and molecule

Molecule

A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...

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