Architects have always sought to make tall buildings safe. This can be done in two ways- first is by using a range of suppression technologies, in other words stopping fires from taking hold in the first place, or limiting their spread if and when they do.
The second was is by extinguishing—ensuring that there are technologies in place to put the fire out quickly if and/or when one starts in the first place.
According to Dr Mark Tatam, building technology director, Kingspan Insulated Panels, the main elements of fire safety for commercial buildings should be approached from a holistic point of view.
“Management of fire load and ignition sources, restricting fire spread and finding ways that occupants can safely and quickly exit the building are amongst the critical factors involved,” says Tatam.
“What we have found in recent times is that the external façade can create a dominating role in fire spread and with devastating consequences, especially when other fire safety systems are not designed to cope with such eventualities.”
“One of the key design elements,” says Tatam, “which can be used to minimise the risk of fires in commercial buildings is compartmentation, or separating the building into fire compartments to stop fire transferring from one area to another.”
“Another is the selection of materials and the use of other fire safety management practices to restrict fire spreading, either internally or externally, in buildings.”
“Highly combustible facades for example, have the ability to spread fire from one part of a building to other areas, and very quickly,” he says.
Using compartmentation to stop fires
As mentioned, one of the most common of the suppression tactics which is used in almost all tall buildings, is compartmentation whereby thick walls and fire-resistant coatings are used to divide a building into enclosed zones, so if a fire does start, it spreads relatively slowly.
Most of the time, compartmentation works, but when it does fail, the result are catastrophic.
This failure usually happens because of penetration like where pipes for heating and water, ducting for power penetrate fire compartments, and those holes must be fire-proofed.
If the fore-proofing was done haphazardly , the fire will use these pipes literally as ‘highways’ to go from one end of the building to another
Currently across Australia, the number of high-rise towers exceeding 100 metres has reached 243, with an additional 252 expected to be built over the next few years.
With so many tall buildings springing up across Australia’s cities, architects are becoming more innovative in designing options for the overall appearance of a structure, most notably its façade.
At the same time, building products manufacturers have also needed to ensure that their products conform to Australian Standards, in terms of fire safety.
Fire resistance level (frl)
According to fire protection technology company Greene Fire, the Fire resistance level (FRL) is defined in A1.1 General Provisions of the Building Code of Australia (BCA) as the grading period in minutes for structural adequacy, integrity, and insulation.
Performance is assessed in accordance with Specification A2.3 of the BCA and given in the format “-/-/-“.
For example, an FRL of - / 120 / - means that there is no requirement for structural adequacy or insulation, and that the element will maintain its integrity for 120 minutes in the event of fire.
Similarly, an FRL of - / 120 / 120 describes an element with no requirement for structural adequacy but which will maintain its integrity and insulation properties for 120 minutes in a fire event.
Greene Fire says that there are five main methods of passive protection are:
Uninsulated fire curtains are cost effective and well suited to the open floor plans that have become the norm in commercial and residential projects alike, but offer no protection against radiant heat.
Insulated walls compartmentalise flames and reduce radiant heat, but can be costly and cumbersome.
Fire rated glass is a viable solution where extensive glazing is desired, but is often very heavy and prohibitively expensive.
Fire doors compartmentalise flames and quell radiant heat, with the added bene t of easy operation in the event of fire. However, they are significantly limited in terms of available dimensions.
Sprinklers and drenchers may cause damage to contents of a space in the event of their use and may be impractical to operate, significantly undermining their efficiency.
What is the difference between Passive Fire Protection and Active Fire Protection?
An integral component of Passive Fire Protection is to contain fires or slow the spread of fire through the use of fire-resistant elements, such as walls, floors, doors and other penetration protection and coatings. Using materials that resist fire, and also that do not emit noxious fumes when exposed to fire can assist with the safe evacuation of occupants and can save lives, assets, and even the entire building.
Conversely, Active Fire Protection comprises systems that require human intervention in order to work in the event of a fire. Examples include fire extinguishers, sprinklers, smoke and fire alarms, and emergency services. This is a reactive approach to extinguishing a fire.
Some common examples of Passive Fire Protection
Passive fire steel protection
According to fire protection systems maker Promat, there are three main types of passive fire steel protection, which may be used separately, although most commonly are used in a combination of two or more.
Spray applied vermiculite leaves a low grade finish and is designed for situations that do not require an architectural finish and/or where cost and speed are critical.
Board encasement systems are fireproof and completely enclose structural steel members thereby allowing for the installation of windows, doors, and walls directly adjacent to encased members. These are designed for high-quality, architectural grade finishes.
Intumescent coating systems are fire-rated coating systems that can be applied directly to prepared steel structural members. They comprises a primer, intumescent,
and top coat. They can be used to achieve a high degree of finish where the exposure of structural steel is required.
Intumescent coatings work by expanding when heat is applied to them. The expanding paint forms an insulating layer of fire resistance, which in turn keeps the temperature of the steel down. This expansion is critical to the performance of the system, so while the initial installation of the product is very thin, there needs to be space around the member to allow for any potential expansion.
One popular intumescent coating is BOSS FireShield intumescent coatings which, when exposed to heat expand and effectively extinguish the flow of heat to the treated surface, prevents the spread of fire, providing precious minutes of fire protection and contributing to the saving of lives and property.
According to BOSS, its FireShield, with Matt or Low Sheen top coats, intumesce and foam into a thick layer when exposed to high temperatures derived from flames or intensive heat radiation from fire.
Why precast concrete is a good passive fire barrier
Unlike many other, especially organic building materials, precast concrete has zero flammability.
The National Precast Concrete Association of Australia (NPCAA) notes that a total precast structure does not need to rely alone on Active Fire Protection systems for its structural integrity.
Often designed as a key component of a building’s passive fire protection, a concrete structure will also assist with the prevention of collapse through structural fire resistance—reinforcing the safety of inhabitants.
Putting the building’s frame in the picture
Following the Grenfell in the UK and Melbourne’s Lacrosse tower disasters, the global construction industry is now more than ever aware of the risk of fire in multi-storey developments. Although in both instances aluminium composite cladding panels were ultimately the culprits, it is now imperative all building construction materials offer adequate protection against fire.
In that respect and in accordance with the Deemed to Satisfy provisions of Specification C1.1 of the National Construction Code (NCC), steel must meet the Fire Resistance Level (FRL) corresponding with the type and class of construction. The NCC divides construction into “Class 1” through to “Class 10” dependent on use, and Types A, B, and C dependent on height. FRLs may vary significantly between buildings of different classes and types.
As temperatures increase, the strength of steel decreases significantly. At 600 degrees Celsius, it has an effective yield strength factor of 0.47, whereas at 800 degrees Celsius it has an effective yield strength factor of 0.11. In practical terms, this means that failure to ensure the adequate fire protection of steel may lead to the collapse of a building in the event of a fire – a fact vividly demonstrated during New York’s, 9/11 tragedy.
The full version of this article will be avialable in the May / June issue 2018 of INFOLINK | BPN magazine.