Fire Safety: Big Mistakes To Avoid

Fire-safety engineering, product appraisal advice and risk assessment are three of the core areas of expertise of consultancy firm Stephen Grubits & Associates Pty Ltd (SGA).

SGA Director, Carlos Quaglia, recently spoke to Building Knowledge about the firm’s expertise and some misconceptions, mistakes and just plain old errors with fire safety that can occur in large building projects without proper knowledge, experience and the right modelling.

One of the first issues Carlos Quaglia addressed is common mistakes when constructing large multistorey residential buildings.

“The main area that defects are found is in the vertical shafts that are provided for distributing services in multistorey buildings.  These shafts, when they are built of lightweight construction, are usually not built exactly to the specification of the manufacturer,” Quaglia explained.

 

“Sometimes the penetrations into those shafts is an area where we often find problems.  For example, if there is a duct penetrating or entering into a shaft, a fire damper has to be provided.

“Now, if there is a plastic pipe penetrating into the shaft, a fire collar has to be provided.  We also have post-construction problems:  once the shaft has been properly built, and with some services that are installed later, not much care has been exercised in making sure the penetrations that are being done, are being done well.”

Quaglia and SGA also stress two important issues for consideration concerning metal beams penetrating fire-resisting walls:

  • The spread of fire through heat conduction along the metal member.  Overheating of the metal member within the unexposed side could ignite combustibles therein, if temperature is excessive.  Fire -protective treatment of the metal member over its entire length is an option however there is potential for reducing the length of protection hence the cost of the protection.
  • Structural damage to the member exposed to the fire could tear the wall down unless the structural performance of the wall is addressed.  Two options are advised:  providing an independent fire-resisting column or embed a column within the wall.  Note that the BCA requirement for fire resistance level of columns could be higher than that of the wall.  If the column is embedded in the wall, also note that the detail of the wall may not be sufficient.  The load-bearing wall has to be designed to withstand the limit-state structural loading under fire

When modelling a theoretical fire, SGA says account is taken of the nature of the combustibles, not just the quantity but also how flammable they are, as well as the location of combustibles, the geometry of the space, venting and the feedback from a low ceiling.

Quaglia said modelling a fire depends also on what type of performance is sought.  Selection of the design fire is made with the intention of assessing the worst case.

“The worst case for being able to predict smoke movement is a fire that produces a lot of smoke, and also a fire that very rapidly achieves a high rate of heat release,” he said. “On the other hand, if we want to model the behaviour of a structure, or the likelihood a structural collapse, then the important thing is how much of it there is, and for how long it’s going to be burning.”

Building Knowledge also asked Carlos Quaglia to explain the latest on active and passive fire protection.“Active fire protection is something that changes its mode when there is a fire, whereas a passive fire protection is always there,” he said.

“For example, a fire-resisting structural member that is being protected with a certain fire-resisting coating, there is a passive fire protection, because it’s always there.  When the fire comes it will just be protected.  On the other hand, a sprinkler is an active fire protection which is always there, but when there is a fire it will change its mode (because water starts coming out of it). “

Quaglia said modern technology has brought about significant advancement in active fire protection – especially the introduction of more affordable computerised processes.

“While some new products on passive protection may have come to the market, the advancement of active systems has been more significant. In parallel with this, more powerful computerised methods of prediction of fire-scenarios have been developed, as well as risk-based methods,” he said.


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