ABSTRACT
You will notice that earlier I mentioned anticipated storage height. The reality of actual building storage and future building use is that due to the ebbs and flows of inventory management, storage is often piled in spots to the highest available height. However, we have no way to predict what the actual commodity storage height will be when a fire occurs. We have to rely on empirical guesswork. The design height can be determined in four different ways:
(1) What the warehouse manager says the storage height will be limited to
(2) The elevation of the bottom of the lowest beam or structural roof member of the building. This is also referred to by those in the commercial real estate business as the building’s “clear height”
(3) The elevation of the bottom of the lowest steel bar-joist web inside the building
(4) 18′′ below the deflector of the sprinkler-heads
In ascending order of common sense, with no. 4 also being the most conservative approach, the designer should make his “storage height” call based on one of the above criteria. Two things to consider here are: 1) the building height need not be considered if permanent storage racks are present and, 2) ceiling sprinkler density will not vary at very high storage heights (such as those in excess of 25′) where in-rack sprinklers will need to bear the brunt of the automatic sprinkler fire-fighting. Fire burns upwards and outwards. Another item to note is that “sprinkler activation can be delayed because of an excessive distance between the sprinklers and the fuel package. The hot gases from the fire plume entrain air, which will decrease its temperature by the time they reach the elevation of the sprinklers” [9].
