High-Rack Storage
FEATURES
SPECIAL RISK FIRES
Photos by Frank Brannigan
There was a time when big fire departments had big fire problems, and small fire departments had small fire problems. As Shakespeare said, “Them days is gone forever.”
All across the country, in urban as well as suburban and rural communities, one-story (100 feet or more in height) high-rack storage warehouses are being erected. And along with these warehouses comes a whole new array of tactical problems and safety hazards that operating fire forces must be aware of.
If a high-rack storage fire is attacked with the same tactics used to successfully mitigate an ordinary dwelling or mercantile building fire, a terrible life loss may result—often involving firefighter casualties.
CONSTRUCTION
A rack storage warehouse represents, in effect, a multistoried building, upwards of 2-million square feet in area, without the resistance to the spread of fire provided by even the poorest floor. Typically, such buildings are rated “non-combustible,” which is a code classification, and not necessarily an accurate description. Just because a building is concrete and won’t burn doesn’t necessarily mean that it is fire resistive. Unless it is fire resistive, it is entitled to disintegrate and collapse in a fire.
“Lift-slab” concrete buildings, with precast wall panels, are very common—and very hazardous.
- The roof is necessary to stabilize the walls.
- Concrete Tee-beam roofs are subject to spalling below its tendons, special high-tensile strength cables used for pre-stressing. Tendons exposed to 800°F (less than a self-cleaning oven) completely lose their pre-stress.
- Wooden roof beams can burn away or fail at the steel splices or connections.
- A 100-foot steel roof beam will expand 9 1/2 inches at about 1,000°F and push the walls down. At higher temperatures, the steel will fail and can pull the walls in.
At a fire in a warehouse under construction, the only fuel was foamed plastic insulation. The roof’s elongating steel bar joists pushed the walls out of alignment. The contractor replaced the tormentors (braces) supporting the walls when the building was under construction. However, the roof was no longer trustworthy.
If the roof is a conventional built up roof of layers of asphalt and paper, it can burn independently of the original fire and elongate the steel bar joists to push down the walls, possibly quite some distance from the original fire. Unless cooled by hose streams, the bar joists will collapse at a later stage.
The sealant between wall panels in these buildings often burns out, and fire shows through the gaps.
The contents of rack storage buildings are normally stored in very lightweight steel framed racks, which are structures in their own right and subjected to the same force of gravity as any building. Since these racks are extremely vulnerable to fire damage and failure, firefighters should never get into a position where the racks can collapse behind them.
Don’t forget to consider the contents of these high-rack storage warehouses. Are they flammable or packed in flammable plastic? Will they absorb water? Six firefighters died when piles of tissues which had soaked up sprinkler water collapsed. Some materials are packed with combustible strapping so that the bundles will collapse in a fire. (The hope is that this will aid” extinguishment by smothering the fire.)
FIRE PROTECTION SYSTEMS
High-rack storage buildings are built to minimize handling costs and maximize profits; fire protection is almost always an afterthought. And although automatic sprinklers have established a remarkable record in extinguishing and/or controlling fires, this record was achieved in buildings with relatively low ceilings and in merchandise piled in relatively solid piles. High-rack storage presents both a greater amount of fuel and an obstruction to sprinkler discharge.
Some years ago, HPR (highly protected risk) insurance companies started conducting tests on high-rack storage. They soon learned that sprinklers located only at ceiling level are inadequate to control fires in high-piled stock, and that aggressive manual firefighting is also necessary. To quote Factory Mutual, “Instead of suppression, we have been forced to accept the concept of fire control.”
Even well-designed layouts with in-stack sprinklers can fail. At one incident, responding units found an “inferno” between two stacks despite in-stack sprinklers. Firefighters backed up the sprinklers and, fortunately, it was possible to position a large caliber stream in a doorway and beat down the fire.
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Photos by Frank Brannigan
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Remember to back up the sprinkler systems to the maximum; and hydrants used for pumpers supplying handlines should be preselected to avoid “stealing” water from the sprinklers. Be extremely cautious of committing personnel insfde the building, particularly when smoke makes it impossible to see what is happening. And don’t be in a hurry to overhaul— stacks may collapse.
An argument rages as to whether it is better to close up the building and let the sprinklers do the job or to vent the structure and attempt a combined manual-automatic attack. The jury is still out on this one.
PREPLAN AND COOPERATION
The only hope for successfully combatting a fire in a high-rack storage building lies in close cooperation between the owner, the warehouse operator, the insurer, and the fire department, including mutual aid companies. Directing operations at a fire in a high-rack storage warehouse requires detailed study and advanced planning. You can’t make it up as you go along.
Every possible scrap of important information should be sought out ahead of time. Get specific information about the sprinklers and water supply (their location and pertinent features), and set forth the special precautions to be taken if sprinklers are out of service. Determine how fire pumps are to be started if they fail to start automatically. Contact the engineers of the insurance company carrying the risk. Study the fire walls and any deficiencies so that pre-assignments can be made to guard weak spots. All information should be in writing and available to the fireground commander.
Be sure that all warehouse personnel on all shifts, including contract cleaners and guards are instructed by their management that the brigade and/or fire department is to be called even if a fire is only suspected.
SUMMARY
A fire in a warehouse, with contents, can represent a possible $100-million loss. Of course, there is insurance coverage. However, in terms of community value, warehouses can rate very high in the risk category when you consider the number of jobs and the amount of tax revenues lost to fire.
With all these concerns of management and workers in the various businesses, the fire service must, as usual, look out for itself. Therefore, the paramount objective of all planning and the main concern during firefighting must be the safety of the fire forces.
