This is part of a multi-post series exploring the most common Performance Solutions fire engineers justify for a typical warehouse building development. For obvious reasons, this post won't reveal the tricks of the trade but instead provides a general overview for architects, project managers and clients to allow informed decision making on the project (and to drive lazy fire engineers!)
The below list was formulated based on our experience on previous projects as the project fire engineer. It is by no means an exhaustive list of every solution that can be blindly applied to any warehouse. Please get in touch with us to discuss your warehouse development and what sorts of solutions we can tailor for you.
Maximum Fire Compartment Size
Background
Warehouse buildings are generally constructed to Type C construction under the National Construction Code (NCC) with regard to fire resistant construction. This is normally driven by costs minimisation for fire rating application to building elements given Type C construction is the least onerous of the three types (Type A being the most onerous!).
In light of the above, the typical Class 7b Type C warehouse building must have fire compartments not exceeding 2,000 m2 in floor area and 12,000 m3 in volume under the NCC 2019 Amendment 1. This has a significant impact on the design of the warehouse as typical storage spaces can exceed 10,000 m2 in floor area.
The Deemed to Satisfy (DtS) provisions allow for this type of situation by creating a "Large Isolated Building" category whereby fire compartment sizes can increase up to 18,000 m2 and 108,000 m3 (they may exceed these limitations as well if fire sprinklers and perimeter vehicle access are provided). The unfortunate part of this is the volume limitation is normally reached well before the maximum floor area as warehouse buildings are, by nature, tall for racking and internal vehicular access.
If the warehouse building does not incorporate automatic fire sprinkler protection and internal fire walls are not desired (for obvious logistical reasons!), there may be fire engineering solution.
Performance Solution
To permit fire compartment volumes to exceed 108,000 m3 in a large isolated building.
The general intent of the 108,000 m3 volume criteria is to limit the volume of potential combustible/flammable storage within the building.
The crux of this type of Performance Solution relies on the storage racking not installed to the full extent of the building height thereby creating an inert volume which is not combustible. This is achieved more often than not with overhead gantry cranes installed or forklift operational limits.
Compromised Perimeter Vehicle Access
Background
As mentioned above, large isolated buildings classified under the NCC generally require a roadway around the perimeter of the building for full continuous access by an emergency vehicle. This allows the attending fire brigade to access and fight the fire at virtually any external point of the building. Requirements under Clause C2.4 (b) of the NCC 2019 Amendment 1 summarised as follows:
Capable of providing means of continuous forward travel from a public road around the entire building.
Minimum unobstructed width of 6 metres with no part of the roadway farther than 18 metres from the building
Must provide reasonable pedestrian access from the vehicle into the building.
Must be wholly within the allotment and be constructed such that it can accommodate the fire brigade vehicle weight and size.
Site and building configurations often will create obstructions which prevent the above provisions from being fully satisfied. This is where fire engineering comes in.
Performance Solution
To permit vehicular access which does not span the full building perimeter
Acceptance of this Performance Solution relies heavily on fire brigade buy-in. Critical to this is their involvement during the initial design phases via consultation meetings with the fire engineer. More information can be found here.
Review of this Performance Solution should focus on the extent of perimeter access achieved and how that can positively impact fire brigade operations.
Extended Exit Travel Distances
Background
For the typical Class 7b warehouse building, the following requirements are applicable for egress travel distances under NCC 2019 Amendment 1.
Up to 20 metres travel to an exit or a point where travel to a choice of two different exits is possible within a total of 40 metres travel.
Given the scale of a warehouse building, it is very unlikely the NCC 2019 Amendment 1 egress requirement will be met. Whether it's the sheer distance between external walls or the configuration of the storage racks, warehouses are notoriously poor for travel distance compliance.
Fortunately, fire engineers are well versed in handling this type of deficiency.
Performance Solution
To permit extended egress travel distances to a building exit
The justification behind this is tricky but the gist of it is that Computational Fluid Dynamics (CFD) simulations are undertaken to model the passage of fire and smoke within the building which is compared to simulations of occupant evacuation. The comparison is of the Available Safe Egress Time (ASET) i.e. the time until the conditions are untenable for occupants and the Required Safe Egress Time (RSET) i.e. the time occupants require to fully evacuate the building. The criterion being:
ASET > RSET x Safety Factor
The tricky part is that CFD simulations are resource intensive and the greater the building size, the more time required to simulate. A separate blog post will be dedicated to CFD basics as it is not the intent of this post to delve into this much detail.
Extended Exit Separation Distances
Background
Exit separation distances are defined for the purposes of providing occupants with alternative choices for exits with a reduced risk of both exits (or paths to) becoming obstructed in the event of a fire. For the typical Class 7b warehouse building, the following requirements are applicable under NCC 2019 Amendment 1.
Exits must be between 9-60 metres apart.
The alternative paths of either exit must not converge to less than 6 metres apart.
Although this type of Performance Solution is less common than extended travel distances due to the vast internal space that come with warehouses, our fire engineers are no strangers to this type of problem.
Performance Solution
To permit extended separation between alternative exits
CFD modelling is also used to justify this Performance Solution. It goes hand-in-hand with the extended egress travel distance Performance Solution.
Extended Hydrant Hose Length Coverage
Background
Similar to extended egress travel distances, hydrant hose length coverage is almost always a problem in large warehouses as hydrants are typically located externally with a maximum reach of up to 60 metres under Australian Standard 2419.1-2005. Once racking is introduced, the issues become amplified.
A good fire engineer can work through this with the fire brigade to reach a mutually agreeable solution.
Performance Solution
To permit the use of a third external hydrant hose length for full building coverage
As noted above, this type of Performance Solution requires fire brigade buy in. As the connection of a third hydrant hose length has an adverse impact on fire brigade set up and firefighting times, the Performance Solution must review how the fire brigade operational response times and how they come to attack a fire on this particular site.
This is commonly demonstrated by completing a Fire Brigade Intervention Model (FBIM). More on this in a future post.
Omission of Hydrant Radiant Barriers
Background
Firefighting personnel are not indestructible when they wear their suits and Breathing Apparatus (BA). They are almost just as susceptible to heat exposure as the average person. As such, Australian Standard 2419.1-2005 requires hydrants located within 10 metres of a building they serve to be provided with radiant heat barrier construction with a Fire Resistance Level (FRL) of 90/90/90.
Often warehouse external walls are not built with a 90/90/90 FRL in mind and to do so may cause operational or financial burden which may not be necessary with the right fire engineering team on board.
Performance Solution
To permit omission of radiant heat barriers protecting the hydrant system
This Performance Solution is slowly becoming redundant with new proposed changes to Australian Standard 2419.1 which permit omission of radiant heat barriers under certain circumstances.
Nonetheless, it still needs to be passed through as a Performance Solution until this new code is called up within the new National Construction Code. The basis for this type of Performance Solution lies in sprinkler protection reducing the risk of radiant heat from the building thereby allowing fire brigade personnel to access the hydrant with less risk of exposure.
Compromised Fire Hose Reel Coverage
Background
Architects and designers alike hate fire hose reels with a passion for their horrendous appearance and general obstruction within circulation spaces. In addition to this, warehouses require a large quantity of FHRs to achieve complying coverage (36 metre hose length with a 4-metre hose stream).
Enter the fire engineer.
Performance Solution
To permit use of supplementary portable fire extinguishers in lieu of full fire hose reel coverage.
Fire hose reels, by nature, are a form of first aid firefighting. They are not used by the attending fire brigade and are intended for occupant use for initial firefighting. It is generally proposed to rationalise the quantity of FHRs by providing supplementary portable fire extinguishers as an equivalent means of first aid firefighting.
ESFR Fire Sprinklers and Smoke Exhaust
Background
It's not a well known fact but Early Suppression Fast Response (ESFR) sprinklers do not play well with smoke exhaust systems as the fans extract both heat and smoke which can inhibit the operation of sprinklers until a point where it may be too late and the fire overruns any suppression system in place.
There is a fire engineered solution though.
Performance Solution
To permit usage of ESFR fire sprinklers in a building with a smoke exhaust system
Partial shutdown of the smoke exhaust system will permit the heat to build up to a point which activates the ESFR sprinklers. Some clever smarts with detection systems and the smoke exhaust controls could allow this to happen but CFD modelling must be able to validate that the partial shutdown does not adversely affect occupant evacuation.
Rationalisation of Smoke Exhaust Provisions
Background
The NCC 2019 Amendment 1 specifies minimum quantities of smoke exhaust fan rates depending on the building class and whether sprinklers are provided. Fire engineers can bypass this generalised cookie-cutter approach and potentially reduce the quantities below this number or even omit the system completely.
Performance Solution
To permit reduction in smoke exhaust quantities
CFD modelling is also used to justify this Performance Solution. It goes hand-in-hand with the extended egress travel distance and extended exit separation Performance Solutions. The intent is to demonstrate that the primary function of the smoke exhaust system is still achieved with the desired configuration and that is to maintain tenable conditions for the period of occupant evacuation.
Conclusion
It's a long read we know! But hopefully it's enough to give an overview of how our fire engineering team could approach a warehouse building development.
If you're ready to move to the next step, please contact us and get the ball rolling!