Lately, we have heard much about fires involving facades of high-rise buildings, and the discussion has invariably turned to the façade materials. When it comes to determining how safe facade materials are in the case of fire can be a tricky proposition unless you know the right question to ask.
Is the material combustible, non-combustible, incombustible, flammable, non-flammable, inflammable? What do these terms mean? Are we using the right terms or even asking the right questions? If we are unsure, who is?
Perhaps we should start with a more fundamental question: can we simply divide materials into two broad camps, those that can burn and those that can’t? This should be fairly black or white, shouldn’t it? Unfortunately, things are rarely that simple. And in our modern world, even simple things are complicated by all sorts of other things.
Starting with the language we use. When we see fire, many words pop into our minds: ignite, burn, blaze, flame, amber, heat, light, smoke, the list goes on. And depending on our technical background, other words may start to creep in: combustion, oxidation, pyrolysis, temperature, radiation...
These words are tucked somewhere in our mind where we compile our own thesaurus. How do we use a single word to describe something that can burn? Burnable, combustible, flammable? We look into our thesauri and our minds tell us that any difference is just a matter of semantics. This is perfectly reasonable in our normal, casual, day-to-day conversations. After all, that is how all our minds work and we understand what they mean in the context of our conversations.
But when we need to be specific in categorising materials to control their use, specialised fields start to emerge. The meanings of the words we though we knew starts to diverge depending on what we aim to achieve.
In the field of dangerous goods, where we manage the transportation, handling and storage of hazardous substances that could readily and violently react with the environments or other substances, we can no longer afford to be blasé in the use of terminology. A slight misuse or misunderstanding could lead to serious consequences. In this field, the United Nations has developed an elaborate, globally harmonised system to classify substances that may explode, combust, oxidise, corrode and other reactions. These are displayed in diamond symbols or placards which you see on aerosol bottles, paint cans, gas cylinders, patrol stations and on trucks.
Substances that could readily ignite and burn are classified as “flammable” or “combustible” depending on their flash points and boiling points. For example, we all know that petrol and diesel can burn, but patrol is “flammable” and diesel, which does not ignite as readily, is only “combustible” and not “flammable.”
If we venture further, most materials we know that can burn, including façade materials, would struggle to earn the diamond labels of “flammable solids” or “combustible solids.” These are reserved for materials such phosphorous, sodium, potassium and other pyrophoric materials that could burst into flames merely via friction or in contact with air or water. Understandably, we do not use these substances to construct tinderbox buildings.
In the building industry, the materials we generally use for construction are benign compared with dangerous goods, although they may be no less dangerous if misused. Unfortunately, we are still stuck with the limited vocabulary that need re-interpretation to suit.
The term “non-combustible” is adopted by our Building Code as the governing criterion for external walls of tall buildings. The “non-combustible” label is given through process of testing, carried out in accordance to AS 1530.1. In a nutshell, this standard is not aimed at checking whether it burns or not, but rather whether it burns beyond the set limits. The standard either deems it or not deem it “combustible” based on the test outcomes. A material that is not deemed combustible would then earn the label of “non-combustible.” For a composite panel, the material in each layer must also not deemed combustible to earn this label. The test is quite stringent. Ironic though it may seem, aluminium composite panels that struggle to earn the diamond label of “combustible solids” in the dangerous goods arena would also struggle to earn the “non-combustible” label as a building product.
There are other building materials that may burn to various extent, but are deemed “non-combustible” by our Building Code. These materials, including plasterboards, need not be tested and are simply “deemed non-combustible.”
The term “flammable” remains in the dangerous goods arena and is not used in our Building Code for building products. It does refer to another term: the “flammability index” which applies only to thin fabric and sarking materials. It is a measure concerning the relative speed of flame spread when the material burns, not whether it burns or not. Hence, having a flammability index of zero doesn’t mean it does not burn.
Unfortunately, we do not have a globally harmonised system for classifying building products. Different countries employ different testing methods and definitions. A non-combustible material in one country may not be non-combustible in another. Some countries test for combustibility, others for flammability. The term “incombustible” is also sometimes used which also mean non-combustible.
Fortunately, “inflammable” is rarely used, since it is not the opposite of flammable - an oddity of English language that could further confuse. All of these differences make it impossible to interpret whether a product tested overseas is what we would label “non-combustible.” It is a confusion that cannot be easily clarified, and the clarifications can easily be confused.
We still see building facades burning, we still see all makes of material used, we still see all sorts of reports, claims and questions. The strategic intent to prevent façade fire is clear, but our statements for the requirements are not, and neither are the measures nor the language we used. In this age of globalisation, where building products could be made and tested anywhere in the world, we desperately need a globally harmonised system for classification of products. A good starting point would be to unify and clarify the language we use.
Until then, me must still ask the right question to get the right answer we need. As for a façade material, asking whether it can or can’t burn is not the right question. Neither is "is it flammable or it is combustible?" To ensure compliance with our Building Code, the right question would be "it is non-combustible?" The response should then either be "it is non-combustible" or "it is not non-combustible." The latter, being a double negative, sounds awkward, but unfortunately, it is the right response to the right question.