The truck was left running with its lights on. When the truck was empty an hour later, the truck driver pulled away from the dock and then stopped to go around and close the trailer doors. As he walked to the back of the truck, he was shocked to see the insulation seal around the dock had caught fire. He sprinted back for his fire extinguisher and was able to quickly douse the fire.
Investigators discovered a seemingly unlikely source for the fire the tiny marker lights on the back of the trailer. As company officials found out, the fire at their dock was far from an isolated incident. Since July 2001, Frommelt Products Corp., a manufacturer of loading dock seals and shelters, has documented more than 80 cases of marker lights igniting compression-style foam dock seals. And Frommelt officials conservatively estimate more than 200,000 dock positions in the United States are at risk for the fires.
"It is cropping up every day now," said Paul Rowlett, Frommelt's president. "People didn't quite know what they were dealing with. They thought they had a dock seal that was being damaged by trailer impact or abrasion. Now, they're finding out that it's burns, not normal wear and tear."
Frommelt's experts initially thought the fires were caused only by damaged lights, where the bulb filament was in contact with the seal, commonly made of vinyl, hypalon or polyurethane foam. But the company's research revealed the burning actually occurs because of the heat generated by the bulbs in a very concentrated area. Chuck Ashelin, Frommelt's director of engineering, said the company discovered three things:
- The marker lights, when insulated by the foam in the pads surrounding them, will gradually create very high temperatures.
- The polyurethane foam used in the pads, when it is heated, will decompose and generate gas that is flammable as well as add heat to the process.
- And finally, the gases can autoignite when the temperatures exceed 800 F without a secondary spark or flame.
In tests of 17 different lights on the market, Frommelt found that some of the lights generated temperatures in excess of 800 F in as little as 30 minutes. "These were the smallest late models, which was logical. They have the least amount of area available to dissipate heat through," said Ashelin. The fires often erupt as the trailer pulls away because the foam is then exposed to oxygen.
While a dock seal can cost several hundred dollars to replace, damage in some of the fires has been much more extensive. Rowlett said damage has spread to building walls, canopies over loading docks and even into trailers, resulting in the loss of the entire contents. Productivity losses compound the damage. "Just the time to evacuate a facility, to pull everyone out and then get them back in, some customers have lost $20,000 to $40,000 in lost time due to the evacuation and then restoring production," said Rowlett.
Frommelt's Insulator dock sealing system uses a Firefighter header seal that combines fire-retardant foam with three layers of foil material to dissipate heat across the header pad, virtually eliminating the threat of fire.
John Hill, a maintenance supervisor at the New York plant, said a post-fire inspection revealed minor burn damage at one other dock seal. The company is in the process of replacing its header pads with the Frommelt product.