BioCycle November 2003, Vol. 44, No. 11, p. 41
EQUIPMENT-wise, 2002 was not such a good year for Gro-Bark (Ontario) Ltd., a composted bark and soil amendment company based in Waterloo, Ontario. On June 1st, a tub grinder with about 300 hours of operating time, caught fire and was destroyed. A temporary replacement grinder was brought in and three weeks later, in the middle of the night, a fire started on an incline conveyor that was being used with the grinder. While not destroyed, the grinder was damaged.
“In the first fire, we suspect that a faulty connection on the electric start gas engine created a spark that caused the dry bark in the grinder to burn,” says Bill McKague of Gro-Bark. “In turn, the plastic gas tank attached caught fire and the grinder burned up pretty quickly. In the second situation, it appears that a hot piece of metal that got twisted along a bearing on the conveyor fell to the ground and got mixed in with material that had spilled off the conveyor. The actual fire started about ten hours after the work with that equipment ceased.”
With close to $1 million in insurance claims, Gro-Bark worked both internally and with its insurer to establish operating and maintenance protocols that are strictly enforced. “For example, our fire prevention guidelines spell out a post shutdown inspection for fire hazards,” explains McKague. “Included is the step of moving a grinder away from the area of operation into a clear area at least 50 feet from other equipment. In order to do that, we have a truck on the site at all times to move the grinder as needed. Previously, with our mobile equipment, we would leave the grinder at a site and use the truck elsewhere in our operations.”
FIRE PREVENTION WARRANTIES
Gro-Bark wrote fire prevention guidelines that are the basis of employee training. On the top of the list is daily maintenance, which includes removing debris and accumulated oil, grease and other flammable material, and pressure washing the tub grinder as needed. “In addition, always get a machine with an air compressor on it, so you constantly blow out radiators and blow away fine dust,” he says. “Blow it out of the engine compartment area and away from bearings. Steps like those just have to be part of the psyche with operators.”
Another critical step when grinding dry and dusty feedstocks like cedar slab wood is to dampen the area around the grinder and spray water into the tub while grinding. This means a water source has to be available on site. The prevention procedures also state to avoid prolonged operation of the hammer mill when the tub is loaded and not rotating. “If the hammer mill gets bogged down and the tub automatically stops rotating, operators have to stop pushing material in there,” adds McKague. “That causes friction and heat, and can lead to a fire, especially with a material like cedar bark. Operators need to be trained to reverse the direction of the tub because you don’t want material hanging up in there at 2100 rpm. The key is to reduce heat build-up.”
For post shut-down inspection, other requirements include: Rake and inspect for smoldering debris (e.g. metal that has accumulated from the magnetic head pulley) that could cause a fire; Stand rear discharge conveyor vertical to remove dust and material from the grinding operation; Check all bearings including hammer mill to ensure temperatures are not excessive. Finally, key to any fire prevention step is having approved, charged fire extinguishers on the machine and on the site at all times.
Gro-Bark’s insurance company put three fire prevention warranties in its policy. The first, the Fire-Watcher Warranty, includes a requirement to have a fire-watcher present during all grinding operations who will be prepared and able to perform fire prevention and protection duties during the operation. The fire-watcher has to remain at the location at least 120 minutes after the operation has been completed. “If the operator leaves at 5:00 p.m., then he needs to shut the machine down at 3:00 p.m. and move it away from where it was operating,” explains McKague. “They can keep working on other tasks, but not grinding.”
The Welding, Cutting, Open Flame warranty applies to any operation that involves an open flame “in any form or manner.” Requirements in this section include: Sweeping and keeping clean the entire area within 8-meters before and during any operation involving an open flame and removing or covering all combustible material with fire-resistant tarps; Hosing down with water the immediate area where such operations will be and have been performed (unless use of water will cause property damage); Having a fire watcher equipped and able to perform fire prevention and protection duties present during all such operations, and remaining in the immediate area for at least two hours after the completion of such operations. The third warranty includes fire extinguisher specifications.
Manufacturers of processing equipment used at compost and mulch production facilities are aware of the fire potential when handling feedstocks like bark, pallets, brush and yard trimmings. “Our manuals recommend housekeeping procedures like blowing off manifolds to prevent fires,” notes Tim O’Hara of Wildcat Manufacturing. An information sheet provided by Peterson Pacific Corp., “Proactive Fire Prevention For Waste Recycling,” points out that “oxygen, fuels and ignition sources are all present when a waste recycler is operating.” It covers housekeeping, operations, emergency preparations, service and special hazards. “We encourage operators to have a daily shut down procedure that includes staying with the machine for some time after it stops operating,” says Becky Smith of Peterson Pacific, who also notes the critical importance of continually blowing the machines clean.
The information sheet recommends positioning the machine so the wind does not blow material onto the engine, and catching “tramp” metal in a container or using water sprays to cool the material (or both). The on-board spray system should be used to wet the material being ground and control dust. All hydraulic and electrical lines should be securely routed to prevent damage or wear, and operators should check for hot bearings, friction heat or loose belts. “It’s also very important to inspect carefully and often for hydraulic or diesel leaks and make repairs immediately,” says Smith.
Continental Biomass Industries (CBI) is making a fire suppression package available with its grinders in the near future. In general, observes Tim Griffing of CBI, fires often are caused by hot pieces of metal that come either from welding or cutting metal, or from metal in materials like construction and demolition debris that gets past the magnet and into the pile of material. They can become so hot they are blue in color. “When doing routine maintenance, like hardening tips, a piece of steel or wire may have wrapped itself around something and the operator is cutting it out, or bolts that need to be removed to change the tips are worn and need to be cut out,” he explains. “The maintenance crew cuts the bolt and molten steel can fly off and into material on the ground. Hot steel also can ignite dust or the rubber on conveyor belts. In general, we recommend wetting everything down, including the grinder chamber, prior to and after any welding or torch work.”
He adds that often, maintenance like changing tips is done at the end of the day, with the crew going home right after. That creates the potential for fires to start when no one is at the site. “It’s a good idea to operate the machine right after the tips are changed to get any of the hot metal out of it and then wet everything down,” says Griffing. Other preventive steps include repairing leaky hydraulic hoses and washing belts after maintenance. In short, housekeeping – before and after operating the machine and after maintenance – is critical,” he concludes.
November 1, 2003 | General
PREVENTING FIRES IN GRINDING EQUIPMENT
BioCycle November 2003, Vol. 44, No. 11, p. 41