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Fire Safety Design: Is an 'Acceptable Solution' design always fire safe?

'Acceptable Solutions' or 'Deemed to Satisfy' documents are extremely useful for completing a fire safety design - but for some buildings it may mean a design which still has safety shortcomings

The C/ASx Acceptable Solution documents published by MBIE are extremely useful documents for not only fire engineers but also BCA's (Building Consent Authorities) , other engineers and even non-engineers, so that agreement on a fire safety design which complies with the Building Code can be reached quickly and easily.

C/AS2 image

These documents exclude large complex buildings (e.g. buildings with atriums, operating theatres, prisons and anything over 20 storeys high), however, even 'simple' or more orthodox buildings within the scope of , and complying fully with, these documents could have residual fire safety risks which are economical and simple to eliminate at the design stage.

A 'one size fits all' solution (such as an 'Acceptable Solution' or design standard ) is only going to be a perfect fit for a small portion of designs and every design should consider the unique risks of that building.

Sometimes, serious risks can be removed without spending that much more …

One example which I included in my presentation at the FireNZ conference earlier this month was a common design for a three storey terraced home. To comply fully with the Acceptable Solution document C/AS1 it needs only 30-minute fire separations to the homes either side and a smoke detector on each floor level. What if you knew that the elderly residents on the top floor level (with hearing difficulties) charged their Li-ion battery mobility scooter (with an 'off brand' charger) in the ground floor internal garage? An internal garage which has no fire separations around it, the internal door could be left open, and is right beside the only fire exit and partially underneath the only stair from the top floor?

For only a few thousand dollars more, the design could include a fire separation around the internal garage (with a fire door on a self closer), some minimal firestopping and an interconnected smoke alarm system which includes a heat detector in the garage (so that a fire here will sound the alert on all floors simultaneously) - some considerable fire safety improvements for mere small change when compared to the overall construction cost.

(Note: the revised C/AS1 document about to be published will have interconnected smoke alarms as a minimum requirement).

Ground floor of a 3-storey terraced home with fire separated garage  and interconnected detection system
Ground floor of a 3-storey terraced home with fire separated garage and interconnected detection system

What does 'Acceptable' really mean in this context?

All designs need to weigh up risk and cost. What is a 'reasonable' cost for an 'acceptable ' level of risk. We could sprinkler protect every single building in New Zealand, but the economic cost would be astronomical and for small buildings with a low occupancy this is clearly excessive. Conversely we could not sprinkler any more buildings, accept the 50?(100?) extra deaths a year from fire and save the country millions! (apologies to my sprinkler supplier and installer peers, but think what we could do with all that spare money!).

The Acceptable Solution documents are a kind of written contract of what we as a society accept as a 'safe enough' building without having to spend an 'excessive' amount to build it.

The Loafers Lodge fire was a terrible tragedy and a lot of the media coverage centered on the question of why wasn't it sprinkler protected? Even if this building were built today, Acceptable Solution C/AS2 would not require this building to be sprinkler protected, yet the media coverage would have you believe that the majority of New Zealanders did not find this building design 'acceptable'..... does this contract need revising?

Loafers Lodge
Loafers Lodge

So what should we be doing better?

To fill this 'gap' between a bare minimum compliant design (which may still have considerable risks) and one that is actually as safe as possible, the 'Health and Safety by Design' (HSbD) philosophy should be adopted in all design work. This philosophy or methodology requires all risks to be assessed at the design stage and eliminated (preferred) or minimised (if possible) with design changes.

This is also a legal requirement under s39 of the HSW Act which states that designers shall remove all risks 'so far as is reasonably practicable' from their designs. So not only do we as designers have a moral/ethical prerogative, but also a legal one, to remove risks from our design.

So, for your next design: complete your bare minimum 'compliant' design (you're most of the way there!) then put aside the compliance documents and take a step back. Assess any residual risks in your design considering such things as occupant characteristics, fuel loads and ignition risk and the risks to any others who may interact with your design through the full building life (e.g. those building, maintaining and demolishing your building, fire service personnel).

Only when you've removed all risks 'so far as is reasonably practicable' is your job done.

Rob Holland BE MEngSt(Fire) CMEng CPEng PMSFPE

Senior Fire Engineer / Director


At Nelligan, we have the expertise to help with the specification and detailing of Fire safety systems on your Fire Safety Design, including Fire Engineering solutions and Passive Fire Protection systems.


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