Although these topics have been addressed in prior articles yet another warehouse was recently lost, due in part because of failure to adhere to three basic principles.
We evaluated eight total loss warehouse fires where sprinklers were controlling the fire, or where the fire was thought to be completely extinguished, and yet ended in a total loss. Three main causes were identified.
Sometimes these factors were combined. These factors were:
- Premature closing of sprinkler valve (twice in the review of these eight incidents with many others occurring),
- Excessive ventilation in six of the eight incidents,
- Not providing a fire watch (with firefighting capabilities) to guard against rekindle while the sprinklers were being restored in three of the eight incidents.
However, first we should review the definition of sprinkler control. So called “control mode” sprinklers are not required or expected to extinguish a fire. They might, but the design basis is to stop the growth of the fire, to keep it from spreading, and to prevent structural failure.
It is expected that the fire service will have to do the final extinguishment. Frequently this will be in an environment of smoke.
Another term associated with modern warehouse fire protection sprinklers is suppression, as in Early Suppression Fast Response (ESFR) sprinklers. Despite widely held beliefs, suppression does not mean extinguishment. It means that the heat release rate is quickly driven to close to zero, but not zero.
Final extinguishment by the fire service and overhaul is still needed. Smoke will not be as severe as with conventional sprinklers because water application begins much sooner and with much greater volume. With in-rack sprinklers the fire is likely to be smaller still, with even less smoke.
Premature closing of sprinkler valves seems to stem from a belief that sprinklers are there to hold the fire in check until the fire service arrives, and then the fire service takes over from there. This is not true.
The fire service is intended to work in conjunction with the sprinklers, not instead of them. Sprinklers should not be shut down until the interior commander is certain that the sprinklers are no longer needed.
Other common reasons given for shutting the sprinklers off too soon are to allow the smoke to lift or to allow the fire to show itself. There are many cases of the fire growing beyond control when this is done. Instead, thermal imaging cameras are recommended to find the seat of the fire.
Once the sprinklers are shut off, someone with a radio on the fire ground channel should be stationed at the closed valve to reopen it immediately if the fire redevelops. This will cause the smoke layer to decend. Interior forces should be prepared for this.
As we just discussed, smoke is to be expected. Personnel operating inside the building need to have a hose line or lifeline to find their way back out. Enough air is needed to get back out. Ventilation is needed but it should be controlled, coordinated with the fire attack, and reversible.
If doors are open for ventilation, someone should be available to reclose them (on orders from the incident or sector commander) if the fire redevelops. Positive or negative pressure ventilation fans (building, fire service, or both) can likewise be shut down.
Large truck mounted fans should be brought up to speed slowly because the large air flow can cause the fire to rapidly redevelop. Irreversible actions such as removing the side of a building allow no way to reverse course if conditions deteriorate.
In almost half of the cases we reviewed, an initial fire was thought to be extinguished and the fire service left the scene. A second or rekindled fire then destroyed the facility because the sprinklers were still out of service from the first fire. It is extra work to provide a fire watch, but far less than the multiple alarm fire that could result.
These simple and basic precautions can prevent a minor incident from turning into a dangerous and resource draining long- term event.