Temperature of sprinklered storage fires

1

C/VM2 sez. for radiation calcs…
The design fire for this scenario comprises an assumed emitted radiation flux from unprotected areas in external walls of the fire source building (assuming no intervention). This shall be taken as:
…
d) 58 kW/m² for FLED for sprinklered firecells not containing a storage occupancy or a storage occupancy with a capability to store to more than 3.0 m

Is my reading of this correct that 58kW/m2 (733 degrees) should be used for all sprinklered fires, or is the intent that it is only for non storage occupancies or where storage is less than 3m. In that case, what radiating output/ temperature should be used? If it is the sprinklered temperature, may as well take the sprinkler system out completely, as that will pay for the hundreds of thousands of dollars of extra concrete walls due to the lesser unprotected area allowed.

Some common sense thoughts

  1. If you plug in some of the numbers in the C/VM2 tables and apply CVM2 allowances for unprotected area, you get more or less the 58kW/m2. Given it is a deemed to comply acceptable solution, the same values should be used for consistency given there is a single Building Code
  2. From the reply from the NZFS to my query, it does not appear that fire spread from sprinklered buildings is an issue and hence it is not a significant problem that needs a large safety factor.
    see https://fyi.org.nz/request/3885/response/12918/attach/5/OIA%202016.815%20Response.pdf. This is backed up by some stats I had from overseas, such as FM Global. interestingly enough in the (US) stats, the age of the sprinkler system didn’t make much difference, whcih is unexpected, as modern storage sprinklers have more science to them than the older systems such as the small bore C/UP heads of NZS4541P.

I know MBIE are looking at rewording this in the new-and-improved VM, but that doesn’t help in the short term

2

Hi Geoff
We are back to the problem of expecting the sprinklers to partially operate. If the temperature of the space is 733C, then all of the sprinklers will activate, and any hope of fire control will be lost - a Vitafoam fire. If the sprinklers do their job, then the worst case scenario is an external exposure of (say) 16m length, with a 2:1 ratio giving a fire area of 130m2, and 16 heads operating. The problem is that the fire area cannot possibly have a temperature of 733C over the entire exposed face, as the hot layer will activate all of the heads within the vicinity. If the reliability calculation is undertaken, then for a robust system it should be possible to eliminate any requirement for exposures to the neighbours to be considered.
I hope to use this argument on my next hypoxic system.
Paul C

3

Geoff,
Since sprinkler systems considering to be sufficiently reliable, your arguments make sense. Where sprinkler system activates, we are dealing with localizes fires, and fire spread from sprinkler buildings is not a significant issue. However, as professionals, we must meet performance criteria of the Building Code. Therefore we must design to C3.9. I believe design fire shall be taken as per estimated FLED, based on the use of the building. We shall allow concession for the sprinkler installation, due to reduced risk of emitted radiation. Currently 50% reduction is permitted in C/VM2 and C/ASx. You are right, it is only a single Building Code, why argue about 58 kW/m2?
Tania