Is Aluminium Flammable? (A Comprehensive Overview)

Is Aluminium Flammable?

In its solid or liquid form, aluminium (Al0) is not flammable. Is worth mentioning that aluminium powder is flammable and explosive, as is the case for many metallic powders. Aluminium alloys with other metals are also mostly non-flammable.

Some chemicals that are made of aluminium, such as organoaluminium compounds, aluminium hydrides are highly flammable, explosive and reactive. Substances in this class are usually only used by specialized professionals and are not present in everyday life.

Aluminium composites can also be flammable.

General characteristics of metallic aluminium (Al0):

  • High affinity with oxygen, easily forms aluminium oxides. Observed on the external layer of aluminium metal that was exposed to air.
  • It is considered a soft metal
  • It is non-magnetic
  • It is ductile
  • The most common isotope is 27Al and the 26Al isotoe is radioactive
  • Aluminium, as far as it is known, is not naturally present in any living organism, however some aluminium salts are somewhat tolerated in biological systems.
Aluminium materialChemical denominationIs it flammable?Is it explosive?
Aluminium in solid formAl0NoNo
Aluminium Powder/DustAl0YesYes
Aluminium foilAl0NoNo
Organoaluminium compoundsExample: Triethylaluminium (CH3CH2)3Al)YesYes
Aluminium HydridesExamples: AlH3, LiAlH4YesYes
Aluminium TrichlorideAlCl3NoSometimes
Aluminium OxidesAl2O3NoNo
Aluminium hydroxideAl(OH)3NoNo
Aluminium AlloysNoNo
Aluminium compositesSome areNo

Aluminium Metal Combustion Reaction

By definition a combustion reaction is one in which a substance is oxidized (meaning an atom in the oxidized substance has its oxidation number increased). Oxidation can be promoted by either oxygen or some other oxydant, not necessarily containing oxygen.

Most flammable materials catch on fire by means of an oxidation reaction. In some cases that oxidation reaction (combustion) does not produce enough energy to cause fire or explosions.

The oxidation of aluminium by oxygen is an example of a combustion reaction. In aluminium solid bars or foils and under normal conditions the oxidation of aluminium takes place at a relatively slow rate. Hence the heat produced is far from enough to cause a fire.

Aluminium metal (Al0) readily reacts with oxygen gas (O2) to form aluminium oxide (III) Al2O3 and carbon dioxide (CO2). This chemical reaction does require a relatively small amount of energy to start, making it an exergonic reaction ( reaction that produces heat).

Alluminium Powder Fire Hazards

In the case of aluminium powder or dust, even though the chemical reaction is virtually the same as in the case of solid aluminium. The surface area of aluminium is far greater in aluminium powder than in solid aluminium.

The larger the surface area, the more aluminium atoms are in contact with oxygen. And so the rate of the reaction between aluminium and oxygen is also far greater, hence energy is released at a faster rate.

The smaller the particles of the powder or dust the higher the surface area and the faster is the combustion reaction rate. Once enough heat is produced by the combustion reaction, this heat promotes subsequent oxidation of aluminium.

Unlike the combustion of a substance in the gaseous state (e.g. propane), the aluminium powder combustion occurs at a relatively slower speed but the heat that is generated per unit of mass is larger.

Aluminium powder is also a lot heavier than gases and so the period of induction of an explosion takes more time than with gases. The period of induction in analuminium explosion may take several seconds, while a gas explosions occurs in a fraction of a second.

The higher weight of aluminium powder also implicates in the possibility of secondary explosions. That is because aluminium powder is hardly completely suspended in the air, it is often in a layer on the surface of the equipment or on the ground.

Usually, the amount of aluminium in the surface of equipment or on the ground is higher than in the aluminium suspended in the air, therefore secondary explosions of aluminium powder tend to be bigger than the primary explosion.

Aluminium powder can also explosively react with substances other than the oxygen in the air. Some acids can react with aluminium.

For instance, if nitric acid (HNO3) goes in contact with aluminium, aluminium (III) nitrate Al(NO3)3 is formed along with hydrogen gas (H2). The latter being highly flammable and explosive. However, such a reaction normally occurs in aqueous solution, not in the air.

Other substances that can oxidize aluminium are alcohols, water, and ozone.

Some precautions notes about aluminium powder or dust are:

  • Finely dispersed aluminium powder forms flammable mixtures with air.
  • On contact with water, acids, alcohol or ozone there is risk of explosions.
  • Avoid the formation of aluminium powder or dust deposis on the ground and on the surface of equipment.
  • Effective ventilation can help with the removal of aluminium powder or dust.
  • Dry sand or special powder should be used to distinguish fires.
  • Organoaluminium Compounds Fire Hazards.

Solid Bulk Aluminium and Aluminium Alloys are Not Flammable

In the years of 2011 and 2020, the Aluminium Association performed a series of tests to further evaluate the fire hazards of solid bulk aluminium and aluminium alloys with other metals.

In both the  2011 and 2020 tests the Aluminium Association concluded that pure solid bul aluminium and all the evaluated alloys were safe to use in regards to fire hazards.

The tests were comissioned by the Fire Technology Department of the Southwest Research Institute.

The test that was conducted on the above mentioned alloys was the ASTM E 136 test. This test consists in using a dry 38 x 38 x 51 mm specimen heated in a small vertical tube furnace at 750°C (1,382°F). 

This temperature is maintained for 30 minutes or until the specimen decomposes.

At least four samples of each alloy were evaluated, to provide a good confidence value, of the four tests at most one can fail in order for the alloy to be considered to pass the criteria.

For the sample to be approved the criteria are: the given alloy surface and interior temperatures during the test must not increase more than 30°C above the temperature measured on the surface of the sample prior to the test and no flaming from the sample after the first 30 seconds.

If the alloy loses more than 50% of its mass during the heating, the criteria are: the temperature cannot go above the stabilized temperature measured before the test and no flaming is observed at any time during the whole test.

Below the alloys that were analyzed in the tests of 2011 and 2020 are listed.


Alloy
Values are given as mass percentage of the maximum content in the alloy
AlCuCrFeMgMnSiTiZn
3003 98 0.51.00.5
500595 – 990.20.10.710.20.30.2
505294 – 960.10.30.430.10.20.1
508392 – 950.10.20.4510.40.10.2
6005A96 – 990.30.30.30.70.50.90.10.2
606196 – 990.40.30.71.20.10.80.10.2
606397 – 990.90.30.71.20.10.80.10.2
6351980.60.61
P1020A >99.6

Conclusions

From what has been exposed in this article, it can be concluded that solid bulk aluminium or aluminium alloys are not flammable.

Albeit when dealing with aluminium powder or dust, great care must be taken. Even though chemically, aluminium metal is the same in both solid bulk aluminium and powder. The reactivity of those materials is vastly different.

Frequently Asked Qestions (FAQ): Is Aluminium Flammable?

Are aluminium sheets flammable?

Aluminium sheets should not be flammable. They do suffer a combustion reaction in the presence of air, but that combustion occurs very slowly. Aluminium sheets are not safe to be exposed to acids or very strong oxidizing agents such as ozone. Since in some circumstances that could lead to fires.

Is aluminium flame resistant?

Bulk solid aluminium or most common aluminium alloys can be heated up to 700 ºC and not catch on fire. Some materials, such as aluminium composites can catch on fire under lower temperatures or under unsual circumstances, such as in the presence of strong acids.

Will aluminium melt in a house fire?

Pure aluminium melts at 660 ºC, that means that it must rise to at least that temperature to start melting. The interior of ordinary flames goes above 1000 ºC. But that does not mean that an ordinary flame is enough to heat aluminium up to its melting point. That means that if a large enough fire to heat aluminium occurs it is possible that the aluminium will melt. Aluminium alloys usually melt at lower temperatures than pure aluminium.

What temperature does aluminium burn?

Solid bulk pure aluminium burns above 2000 ºC. The burning temperature depends on the amount of oxygen that is in contact with aluminium. Aluminium in powder form burns at quite lower temperature than solid bulk aluminium or aluminium foil.

What metals are flammable?

When considering metals in their bulk form, flammable metals include: sodium, potassium, uranium, lithium, plutonium and calcium. These metals are extremely reactive with water, producing hydrogen gas, which is also considerably dangerous.

Is burnt aluminium foil toxic?

If one can heat aluminium foil to the point where it burns, the fumes released will likely contain toxic particles derived from the oxidation of aluminium. Since the heat to burn aluminium foil is very high many everyday materials that are eventually around can also catch on fire.

What fire class is aluminium?

Aluminium in its bulk form is classified as A1 by the European Union. A1 means that the material does not contribute to fire. Aluminium in finely divided particles such as in powder or dust form is far more dangerous.

What is correct aluminium or aluminum?

Both forms can be used, and both refer to the same chemical element or the same material.

References

Kaufman, J. Gilbert, Fire Resistance of Aluminum and Its Alloys and Measuring the Effects of Fire Exposure on the Properties of Aluminum Alloys, ASM International, 2016.

A.A. Gromov, A.Yu. Nalivaiko, V.P. Tarasov, S.V. Zmanovsky, A.N. Arnautov, A.V. Sergienko, K.B. Larionov, Chapter 5 – Aluminum Powders for Energetics: Properties and Oxidation Behavior, Editor(s): Qi-Long Yan, Guo-Qiang He, Pei-Jin Liu, Michael Gozin, In Micro and Nano Technologies, Nanomaterials in Rocket Propulsion Systems, Elsevier, 2019, Pages 151-173. https://doi.org/10.1016/B978-0-12-813908-0.00005-8.

Information about aluminium powder hazards: https://inchem.org/documents/icsc/icsc/eics0988.htm

https://www.nj.gov/health/eoh/rtkweb/documents/fs/0054.pdf

What was missing from this post which could have made it better?

Leave a Comment