Is Alucobond Flammable?
Alucobond cladding is not considered flammable. For detailed information the technical and safety data of the specific material must be consulted. Any installation of aluminum composite cladding must be in accord with the competent local authority.
Alucobond and other aluminum composite cladding are aluminum composite panels. This cladding material is made of two external aluminum composite based sheets, between these aluminum sheets is an organic polymer core.
The organic polymer that makes up the core of aluminum composite panels is usually high density polyethylene or high density polyurethane. Both of which, by themselves, are considered combustible materials (not necessarily flammable).
Aluminum composite panels have been extensively used for cladding in building and in houses. Over the past decade, a significantly large number of fire incidents have been related to aluminum composite panels.
In the past few years the competent fire authorities have been developing standards for identifying dangerous usage of aluminum composite panels on houses and buildings.
Some Fire and Thermal Characteristics of Aluminum Composite Panels
The aluminum composite sheets of aluminum cladding are fire resistant, non-flammable and non-combustible. Aluminum is however, a good thermal conductor (239 W/m.K at 20 ºC and 1 bar).
The high thermal conductivity of aluminum does not necessarily translate to aluminum composites in aluminum claddings. Each different composite has different properties. Nonetheless, thermal conductivity is an important factor.
If the polymer core catches on fire, the aluminum composite sheets can lead to heat propagation.
The highest fire hazards associated with aluminum composite panels are the polymer core. The two most commonly used polymers, high density polyethylene and polyurethane are combustible.
Combustible materials are capable of catching on fire if in contact with an ignition source under the circumstances they are in.
Aluminum Composite Panels in High Buildings Pose Higher Risks
Aside from the risks associated with the combustibility of polyethylene core in aluminum composite panels another problem lies in high buildings using this type of cladding. That is because fires in the exterior of buildings are considerably hard to control.
What are Aluminum Composites?
A composite is a material made from combining two different substances – usually with very distinct properties. Aluminum composites are ‘mixtures’ of aluminum with another substance.
What is Polyethylene?
Also called polyethene, poly(methylene) or just PE. Polyethylene refers to any polymer which has the group CH2CH2 as the monomer; a common representation is CH3(CH2CH2)nCH3.
The number of monomers (n) in each polyethylene polymer can vary substantially, from a few dozens to thousands.
Thermal and mechanical properties of polyethylene also vary significantly. In general polyethylene with more monomers (higher n) will have higher mechanical and thermal resistance. Density and molecular weight also increase along with the number of monomers.
Overall, polyethylene with lower number of monomers are more easily ignited than higher weight polyethylene, meaning higher weight polyethylene is less flammable than lower weight polyethylene.
Polyethylene in Aluminum Composite Panels
In the case of aluminum composite panels, the used to compose the core of the cladding is high density polyethylene (also called HDPE). HDPE is defined as a polyethylene with a density equal to at least 0.941 g/m3.
HDPE has higher mechanical resistance than low density polyethylene and provides insulation in buildings. HDPE has a melting point in the range of 120 to 130 ºC.
It is polyethylene that makes aluminum composite panels to be flexible and light. At the same time, polyethylene confers some fire hazards since it is strongly combustible.
Polyethylene Thermal and Fire Properties
Polyethylene molecules are composed of carbon and hydrogen atoms, the same is the case for the main substances in gasoline, natural gas, methane, and some airplane fuels. The main difference between these materials is the number of carbon and hydrogen atoms in each molecule.
Polyethylene has up to thousands of atoms in each molecule. In terms of their likelihood to undergo a combustion reaction, this means that it is harder for their chemical bonds to be broken.
On the other hand, once a combustion reaction takes place on polyethylene, a relatively high amount of heat is produced. One of the reasons for this is the high number of chemical bonds that are formed in the products of the combustion reaction (water and carbon dioxide).
For comparison, for methane (CH4) to undergo a combustion reaction, four chemical bonds are broken in each methane molecule and six new chemical bonds are formed in the products (water, H2O and carbon dioxide CO2).
While for polyethylene the number of chemical bonds broken is proportional to the molecular weight of the given polyethylene. The number of chemical bonds involved can go as high as tens of thousands.
Roughly speaking this translates to polyethylene being less flammable than methane but having a potential to burn hotter.
The combustible ratio (a property that indicates how much heat a given material releases once ignited) of high density polyethylene is around 25. What this means is that if polyethylene starts burning the amount of heat generated is 25 times the heat that is required to ignite.
This heat is more than enough to cause polyethylene near this heat to also start burning.
What is Polyurethane?
Some metal composite panels, including some aluminum composite panels, utilize polyurethane in their core.
Polyurethane refers to any polymer that has urethane monomers bonded (linked) by carbamate functional groups (-OC(O)NHC-).
Like the vast majority of polymers, polyurethane has a wide range of polymerization (the degree of polymerization indicates how many monomers the given polymer molecules are composed of).
Is Polyurethane Flammable?
Most polyurethane varieties are flammable and all of them are combustible.
Flammable polyurethanes are the ones with lower density and molecular weight.
Higher density polyurethanes may only ignite at temperatures too high for this material to be considered flammable.
Nonetheless, all polyurethane is considered combustible since all of them are capable of being ignited. The heat produced by burning polyurethane can easily be enough to self sustain a fire caused by the burning of this polymer.
Therefore, unless a polyurethane fire is extinguished by an external source the fire will continue until all the polymer is consumed.
Fire Accidents Related to Aluminum Composite Panels
Recent tragedies that have been directly correlated to aluminum cladding include the
London Grenfell Tower in June 2017 and the Melbourne’s Neo200 building February 2019.
Uses of Aluminum Composite Panels
Aluminum composite panels and metal composite panels are popular assemblies mainly for the following reasons:
- They can contribute to energy efficiency for the building
- They can help prevent rain and moisture penetration
- They can attribute buildings with a clean, modern appearance.
In summary some facts regarding aluminum composite panels have been presented and briefly discussed. Deeper insight was given in regards to two of the most commonly used polymers for the core of sandwich panels, high density polyethylene and polyurethane.
After the large number of fires caused or made more severe by aluminum cladding, this type of cladding has been more cautionally looked at both by governments and developers.
Frequently Asked Questions (FAQ): Is Alucobond Flammable?
Is aluminum non-combustible?
Under normal conditions aluminum is non-combustible. Under very high temperatures aluminum can be combustible. Aluminum in dust or powder form is flammable and combustible. In the case of aluminum composite panels there are two points to be considered. The first is that the aluminum used in cladding is not just aluminum it is aluminum composite, which can have properties quite distinct from pure aluminum. The second important point is that both aluminum and aluminum composites can be good conductors of heat. If a high enough amount of heat is subjected to aluminum composite panels, heat can be conducted to the polymer core. Which in turn can cause the polymer to undergo undesired transformations such as increase in mobility.
Is Dibond combustible?
Dibond FR (Fire Retardant) has been specifically developed to withstand contact with flames. Unlike the types of cladding discussed in this article which use polymer based cores, the core Dibond FR is composed of mineral based material.
Can alucobond be curved?
Yes, some Alucobond products are designed to be able to be curved in order to afford desired architectural structures. Specific information is provided by the company 3A which is responsible for Alucobond products.
Is PE cladding flammable?
The polyethylene core in cladding can catch on fire if in contact with flames or sparks. The whole cladding is made of non-flammable components, the metal composite layers. The specific hazards should be provided along with the specific cladding product and the proper safety standards must be verified with the competent local authority.
Is aluminum composite heat resistant?
More recent aluminum composite panels have heat resistance, nonetheless the specific fire resistance varies from each material. There are many different types of aluminum composites and each one has its limits and recommendations. In 2019 and previous years, severe fires have been directly related to aluminum composite claddings.
Will aluminum melt in a fire?
Pure aluminum melts at 660 ºC; a normal fire is not capable of heating aluminum up to this temperature. Moreover, aluminum composites may have higher melting points than pure aluminum. However, aluminum can conduct heat to other materials that do melt at lower temperatures.
How do you know if a cladding is combustible?
In order to be sure if a specific cladding is combustible it is necessary to know exactly what materials composed the given cladding. This information should be provided by the product developer. Moreover, some materials are non combustible at normal temperatures but may turn combustible at higher temperatures. Other more specific factors, such as humidity, oxygen content in the air, the presence of chemical vapors, may also change whether or not a material is combustible.
Grenfell fire incident:
Aluminum thermal conductivity:
J. Carvill, 3 – Thermodynamics and heat transfer, Editor(s): J. Carvill, Mechanical Engineer’s Data Handbook, Butterworth-Heinemann, 1993, Pages 102-145, ISBN 9780080511351, https://doi.org/10.1016/B978-0-08-051135-1.50008-X.