Most modern and elevated multi-storied structures (sports arenas, airports, train stations and so forth – elements we refer to as the built environment) are built from a steel skeleton. That is the structural elements are steel based. Given steel has numerous advantages – strength, price, access, and resistant to fire – it is a leading building material today. However, where a fire gets hot enough, and lasts long enough, the steel itself can start to warp and lose its strength.
Australian Building Code requires all new buildings to have structural steel fire protection in place prior to obtaining final completion certificates, however, as we have seen for too long and too often, despite knowing that a project will require intumescent protection of some description, the decision as to what is installed is left till the 11th hour of the build process, thus restricting the options available.
In this article, what we want to do above all else, is help more people understand that the plan and design of a structure, should include the scope and specifications for passive fire rating, including, the FRL required across all aspects of the building, the preferred products and as required, the top coat to finish the job with.
Fire rating as a concept
As you will know from previous blogs, or our site itself, the term “fire rating” is incredibly broad and often misinterpreted. What the term does mean (and indeed the proper terminology under the Building Code of Australia), is fire resistance level or FRL. Where fire rating plays a part within the varied elements of a FRL, the two are not equivalent or interchangeable. To help you better understand the aspects which form an FRL and how they are determined, we have compiled a quick refresher for you below.
FRL is technically defined as an expression of; Structural adequacy/integrity/insulation or SA/INT/INS
- Structural adequacy is defined as measure of a tested assembly to be load bearing, or carry a preset load, in fire conditions. The measure is relevant for wall systems and not door & frame systems as door & frame systems do not have load bearing ability of their own.
- Integrity measures an assembly’s ability to restrict the passage of flame and hot gasses but does not address smoke leakage.
- Insulation addresses a fire resistant product’s separating barrier temperature as measured by the rise in temperature on the non-exposed, or non-fire side.
The number of minutes in which there is no failure when tested in accordance with AS 1530 Part 4 fire test criteria determines the passing value. So a fire resistance level expressed as 60/60/60 implies that every component passed for that range of minutes: SA = 60 minutes INT = 60 minutes INS = 60 minutes.
Why fire rating should be primarily considered at the designing stage
At all times, we will advise clients and seek to educate engineers and architects, that choosing a fire protection system for steel structures is a complex issue that is best decided in the designing stage of a construction. We make this recommendation because issues that may prove unsolvable in the later stages of development are forestalled, thus reducing costs, helping prevent project timeline collapse and allowing the best products to be used.
Key determinants that will affect the choice of product includes:
- The natural conditions to which the steel structure is exposed to. It is important to note whether the steel being protected is internal, semi-exposed (various projecting roofs, etc.) or external. Rain, and other elements affect solutions differently.
- It is additionally important to know if high humidity, a corrosive atmosphere or any other special conditions might occur.
- Whether or not the steel being protected is hidden from view or is to be an architectural feature. Design criteria should always be factored in.
- The critical temperature at which the particular individual steel member loses its load-bearing capacity at a specific load should be determined during the design phase. This will affect the selection of the right steel members and the choice of product required to achieve the specified FRL.
- It is important to note, that a steel member which is exposed on 3 sides will have a different temperature growth rate to one exposed on 4. Similarly, different thicknesses of steel will affect the steel temperature over time.
Role of FRL in choosing the right steel
Put simply, when the fire rating requirements of your project are scoped, factored and planned for early in the project, the options available – whether the choice of product, the size of steel or other factors – are opened up. Furthermore, planning allows for construction choices to be made, such as onn-site or off-site application, product selection, and therefore as a combination of these two items, applicator. Evidence is increasingly showing that projects where the steel is coated with thin film intumescent – such as SC803 – off-site the project costs come down and the timeline is condensed.
Another important reason to consider FRL during the design phases is the overall architectural vision and aesthetics of a construction project. Whilst it may be difficult to put a value on the different elements of design, the fact remains, that architectural elements are important. But the decisions made which affect the design will also affect the choice of steel used, the FRL required and therefore the products used.
It should be noted that designing for aesthetics naturally costs more. In cases where more steel needs to be exposed the odds are, the expense will increase. In such situations you will need a low build product which can be top coated, allowing you to design to specification and then style for required interior design. Nullifire’s range of products are designed to require low film thicknesses, allowing for top coating.
To us, the choices, the factors to consider and the elements which affect a project are all straightforward, but then again, this is what we do – day in and day out. But if you are confused, need help or want more information about what fire rating considerations you need for a building you’re planning to build, consult with one of our specialists at Permax. Give us a call, or shoot an email through, we’re happy to help.
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Permax constantly update the documentations based on the new fire testing outcomes and change of standards and regulations. To ensure the documents you read are up-to-date, please contact the Permax technical team.