Protecting warehouses from dock seal fires
Jan 1, 2004 12:00 PM
With materials handling equipment running in all directions and backup alarms going off constantly, loading docks look and sound dangerous. They are; just a moment of inattention can result in an accident. Fire, however, on a refrigerated dock usually doesn't top the list of potential dangers, especially not a fire that starts in the foam dock seal designed to help maintain temperature integrity. The danger is real and has been made more so by a relatively recent change in federal regulations governing van trailers.
The potential cost of a dock fire can be devastating. Simply start with the value of the trailer and its cargo at the door where the fire begins. If the fire manages to spread into the warehouse, costs escalate rapidly. One warehouse fire that started in a dock seal cost a grocery chain more than $20 million. Even if the fire is minor, costs for building evacuation and temporary shutdowns can be substantial. In addition, the door must be repaired and the seal replaced, both situations that result in lost warehouse productivity. Following a fire, insurance premiums always increase. Of course, legal fees become a part of the equation as responsibility for the fire is being settled. None of these costs takes worker injury or death into account.
Dock fires are not new. In fact, they have been increasing. Armed with this knowledge, Frommelt Products Corporation has looked extensively at damaged dock seals and determined the most likely reason for the fires. Beginning in July 2001, Frommelt personnel have looked at more than 100 burned door seals. Until this research, most seal damage was diagnosed as normal wear and tear from trailers backing into the seals. In a few cases of more severe damage, burns have simply been listed as “cause unknown,” says Chuck Ashelin, engineering manager for Frommelt Products Corporation.
Marker lamps generate heat
The cause now is known. Fires can happen when lit trailer marker lamps are compressed against a dock seal. Frommelt says that as many as 200,000 dock seals could be involved as potential fire hazards and that the number of fires is likely to grow in coming years. Although a fire is not always the result, the one factor found in most fires has been trailers parked at the dock with the tractor engine running and lights left on.
Field studies have shown damage to seals ranging from small scorch marks on the seal surfaces to burned cavities inside the foam varying in size from a marble to as large as a grapefruit. Fires spreading out of the foam can damage doors and walls extensively as well as trailers and cargo.
Tests have proved that bulbs in trailer marker lamps can generate enough heat to melt or burn vinyl, hypalon, and polyurethane foam, all typical components in a compression-style dock seal. Individual marker lamps can build to a high temperature in a small area precisely because the foam dock seal acts as an insulator, preventing the heat from escaping. An ignition source such as an exposed bulb filament is not required to start a fire.
Extra voltage speeds heating
Most trucks are equipped with standard 12-volt electrical systems. However, many tractors generate extra power to supply appliances such as refrigerators, televisions, microwave ovens, or video tape players often carried in the sleeper berth as driver conveniences. In such a case, power output may be as high as 14 volts. The extra power does not cause fires, but it can speed the process, Frommelt says.
Tests with undamaged marker lamps compressed into a foam dock seal have shown temperatures as high as 900° F at the point of contact between the lamp and the seal material. This is well above the flame ignition point of urethane foam. Temperature can rise to that point in as little as 20 minutes. Even warehouses with “lights off” policies have had problems with dock fires.
Tests also have shown that urethane foam can ignite at temperatures around 800° F when exposed to an abundance of oxygen. This situation occurs when a trailer pulls away from the dock and air is drawn into the previously compressed foam. Such a fire can completely engulf the header pad of a dock seal in as little as a minute.
The problems of dock seal fires are compounded by confusion in specifying dock seal material. Mostly the confusion revolves around the difference between fire retardant and fire resistant materials. Nearly all dock seals are offered with fire retardant fabric and foam. However, this material does not prevent damage. Instead, it is designed to extinguish itself after it catches fire to prevent a larger problem. Almost by definition, fire retardant materials must begin burning in order to work, Frommelt says. This means that warehouse components can be damaged even if fire retardant materials are used and if they work properly.
Fire resistant materials, however, will not catch fire from the heat generated by marker lamps. In addition, technology is available to limit marker lamp temperature to a maximum of 400° F, well below the ignition temperature of urethane foam.
The first step in dock fire prevention is to realize the nature of the problem and to know that the potential for fires is rising. As recently as 10 years ago, few trailers had marker lamps across the top of the rear frame. However, Federal Motor Vehicle Safety Standard 108, which became effective in 1999, mandates clearance lamps at the top rear of van trailers. The risk from these lamps will remain until the trailer population is replaced with vans using LED lamps that do not generate heat.
Until trailers no longer provide a heat source, the best solution is to inspect dock seals for signs of burn damage and to replace damaged components with fire resistant material. Fire retardant material is not a solution, Frommelt says. Entire fire resistant dock seals are available as are individual components such as head pads and curtains.
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