Sprinklers Protect High-Rack Warehouse
Fire protection in the new high-rack warehouse of Nabisco, Inc., is provided by a zoned deluge sprinkler system.
The system, designed by Grinnell Fire Protection Systems Company, Inc., is engineered to put water on the fire in its early stages through rapid detection. The use of zones limits the area of water application in the event of a fire.
The Nabisco production plant, which opened last October in Henrico County, Va., just outside Richmond, includes one of the largest high-rack warehouses in the country. The highrack storage area is 425 X 80 feet with a basically flat roof 75 feet high. The four double racks (with provision for a fifth) are each 381 feet long by 68 feet high. There is a 6-foot aisle between racks. The back-to-back racks have a sheet metal baffle separating them to contain heat and water spray.
Automatic detection vital
The warehouse, which can hold almost 5000 1-ton pallets of baked goods, is completely computer controlled with four automatic stacker cranes operated by one man in a control room. Thus, the warehouse is mostly unoccupied, which makes an automatic detection system imperative for the fire protection system.
Protection for the 34,000-squarefoot warehouse is divided into zones— one for each of the four facing racks. Each zone is in turn divided into five subzones with a subzone covering about 80 linear feet of rack from floor to roof. The baffles separating the back-to-back racks limit the fire zone to the two racks facing each other across an aisle.
Deluge nozzles mounted on the faces of the racks spray horizontally into racks across the aisle. The open nozzles are staggered in a grid so that their alternating cones of spray complement each other instead of spraying directly into each other.
Heads also in racks
If a fire is detected, all the nozzles in the subzone containing the fire will flow simultaneously from the top to the bottom of the racks. There are also a few heads in the racks to check the chimney effect of fire that is common to high-rack storage.
Grinnell reports that its high-rack deluge system requires a water application rate of 0.15 gpm/sq ft. This can be compared to conventional roofmounted sprinkler systems that require a water application rate of at least 0.4gpm/sq ft.
The detection system developed for the Nabisco warehouse by Alison Controls consists of approximately 300 feet of continuous thermistor strips in each zone, installed at four elevations. (Other types of detection systems can be used.) The detection strips are connected to an Alison Control Model 6007 control center console in the control room, where it can be supervised by the warehouse operator. Auxiliary warning panels are in the guardhouse outside the building and in the maintenance superintendent’s supervision area to take care of the hours when the warehouse is not in operation.
The control panel normally is in an electronically locked condition to prevent accidental tripping of any of the systems. If any of the sensing strips detects a temperature of 175°F, however, the equipment rings a pre-alarm bell on the panel, sounds a siren outside the building and unlocks the activating buttons. Lights on the panel correspond to the zones in the warehouse, so the operator knows the location of the temperature condition.
The operator can then activate the system from the control panel or go into the warehouse to find the reason for the alarm. The system also can be activated manually at the valve in the warehouse.
If the temperature should continue to rise 20°F above the pre-alarm temperature (to 195°F), equipment in the control panel automatically activates the deluge system in the affected zone. The time from the tripping of the valve until the deluge is released is approximately six seconds. In case of power outage, the detection system is designed to operate on its own batteries for up to 100 hours.
The water system consists of three 2000-gpm pumps in a pump house away from the plant building. The one electric and two diesel pumps, capable of providing 125 psi, take suction from two 500,000-gallon aboveground water tanks and pump into a 12-inch underground loop around the building. The tanks can maintain a 120-minute water supply with all of the plant’s fire protection systems in operation.
The underground loop leads into the high-rack area through five separate 8-inch lead-ins, feeding five 8inch manifolds—one for each primary zone in the warehouse with provision for the fifth zone. At each manifold, there is an electrically controlled deluge valve for each subzone. This provides coverage for any subzone individually, but both water supply and pump capacity are designed to provide adequate water if two of the subzone systems are activated simultaneously.
As part of the plant protection system, hydrants and hoses are located both inside and outside the building.
To prove the practicality of the deluge system, tests were conducted jointly by Grinnell and Nabisco at Grinnell’s facilities at Cranston, R.I. Six tests were made using combustible packaged biscuits mounted on wooden pallets covered entirely with polyethylene shrink film. The fire was extinguished in less than five minutes after detection in all tests. Also 97 percent of the biscuits were classified as usable after all six tests. They had been protected against water and smoke absorption by the polyethylene film. No structural damage to the rack was noted.
Shrink-film unitizing will protect goods near the fire from water damage, but the contention from insurance interests was that the film was highly combustible and increased the fire hazard. The tests showed, however, that the fire burned slowly, consuming primarily the shrink film as it worked its way around the outside of the load at the ignition point. In some cases, the film on the loads above first relaxed and then billowed as the rising combustion gases got underneath. The billowing acted as a check to reduce the chimney effect in the stack and when the detection system triggered the water spray, the shrink film actually aided dispersal of the water around and between the racked loads.
Another test was requested by a manufacturer of polyethylene bags. The bags, in sheets, wrapped around corrugated kraft paper, were racked in loads of palletized cartons. The cartons were laid on the pallets so there were tunnels between each, allowing a fire to easily burrow into the load. Within a minute after ignition, the fire shot up the flue and enveloped the third tier of pallets directly above the ignition point.
Monitored by various heat, flame and smoke detectors, the nozzles came on in 65 seconds. At 2 1/2 minutes, the fire was under control and 15 seconds later, it was visually out. Apparently, however, the fire burrowed into tunnels between the cartons and it had to be extinguished with a hose.
The zone deluge system had controlled the fire and saved other goods warehoused nearby, but it was found that there was a need to get water into the inner core to penetrate the burning plastic. The test was not repeated.
Another test was conducted with racked loads of books and paper forms that were extinguished within 10 minutes. No structural damage to the racks was noticeable and, though the two-way, edge-supported pallets were burned, they did not collapse in the racks nor when removed by a fork lift.
After the biscuit tests, the insurance company having jurisdiction accepted the 26-foot-high tests (maximum height of the racks in the Grinnell test center) as representative of a 60-foot high-rack storage situation because the fire never reached the top of the test rack.