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Requirements of Fire Rating for Steel

Aug 17, 2020

Whilst there has been a subtle shift in recent years back to more sustainable building materials such as timber, the predominant building materials (for now at least) remains steel. 
Whilst there are many advantages for construction (versatility, strength and durability to name a few),  the fact remains, that failure to ensure adequate fire protection measures are implemented - passive fire protection included - may lead to the collapse of a building in the event of a fire.  It is because of this that fire rating products have been produced, refined, and improved over the years.
Today, fire-resistant paint such as thin-film intumescents can be applied to steel to improve performance in the case of fire which is definitely good news, right!?
But the question remains: how can we effectively protect steel from damage in case of a fire? Let’s go through the fire rating requirements that you need to consider.

But before that, let’s have a quick refresh about what happens to steel when exposed to fire.

When a building catches fire, the flammable materials are the first things to be destroyed. We’re talking, printer paper, furniture, carpet etc. As the fire ramps up in heat (and it does, very quickly – reaching temperatures of 500 degrees Celsius within 5 minutes) the level of damage can potentially become excessive, enough for it to affect the structural elements (bricks, steel and concrete), causing the collapse of the structure. That is why, fire rating prior to construction, is important.
Steel, being one of the most commonly used building materials, is proven to be highly durable however, it is vulnerable to structural decay when exposed to excessive heat. And when the temperature keeps increasing, it starts to lose its strength, contracts, and changes in dimension, which will ultimately lead to the collapse of the infrastructure.

Did you know that when temperatures exceed 550 degrees Celsius, steel loses its specified margin of safety?

Fact: Steel softens at 1000 degrees Celsius. But what many people are unaware of is that the Australian Steel Institute has reported that steel begins to lose its specified margin of safety once temperatures exceed 300 degrees C and this accelerates quickly after 400 degrees.
 
But many types of fires reach higher temperatures than the defined safe limit value. Cellulosic fires, for instance, can reach temperatures of over 900 degrees Celsius. At this point, steel will begin to deform and expand. Internal stresses can occur that create warping and acause the steel to lose more of its strength and integrity.
 
The crux of what we are saying is that yes, steel is strong, however, fire will weaken it significantly and relatively quickly. So it becomes essential that specifiers consider the best ways to balance design function, fire performance and aesthetic objectives. We advise that during construction builders are called upon to use fire-resistant paint for metal in order to provide an additional layer of protection to structural steel. Nullifire, for one, has a range of intumescent paints that can protect structural steel for up to an FRL of 120 minutes, achieved by protecting the steel temperature, through a protective char that forms during exposure to heat.

What are the requirements for fire rating performance?

Australia’s National Construction Code (NCC) has guidelines that define performance requirements for buildings exposed to fire with the primary goal of ensuring the safety of occupants. These requirements can be met by either one or a combination of two distinct approaches: the Deemed-to-Satisfy (DTS) Solution and the Performance Solution.

  • The DTS Solution makes use of a range of prescriptive requirements. It typically focuses on the assessment of individual elements to ensure that all critical points are met. It also includes compliance to the relevant standards.

  • The Performance Solution allows people to satisfy the requirements through alternative means. Due to a better understanding of real-world fires, this performance-based approach can provide a better fit to actual or near-actual fire scenarios that can be met by a range of acceptable solutions.

Some of the requirements that need to be considered before specifying fire protection for steel include:

  1. Steel serial size. This refers to the dimensions or designated profile of the material. It is an important element in calculating the total volume of the steel section subject to fire protection.

  2. Number of exposed sides. Different sections of structural steel have varying exposed sides. For instance, a beam attached to the wall has 3, a freestanding column has 4. It is important to know the number of exposed sides because the numbers will tell you at which temperature the structural steel will fail.

  3. Fire Resistance Level (FRL). National regulations prescribe FRL requirements for buildings depending on different configurations and types of occupancy. The ability to withstand a fire load is based on a standard test of an individual element using a prescribed load. The level of required fire protection can vary depending on the approach used (DTS or Performance).

  4. Critical temperature. This refers to the load the structural engineer has used in their design. An often-used criterion for this is 550 degrees Celsius for most fire protection materials. However, it could be less or more depending on certain factors, so it has to be checked carefully to maintain a building’s load-carrying capacity and integrity during an outbreak of fire.

Permax can Help with Your Fire Rating Needs

Advances in the understanding of how fire behaves in different structures and how steel reacts to fire have led to the development of cost-effective fire engineering solutions. The introduction of innovative products like intumescents (SC803 for example) has also helped to reduce the cost of protecting steel structures.

If you are looking for a fire rating product that will provide the best fire protection for your structural steel, consult our Nullifire specialists at Permax today.

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