Taking the Heat: Heavy equipment needs fire suppression
Mining vehicles, for both operations under and above ground, experience some of the toughest working conditions of any mobile machinery in commercial service today. In addition to rigorous duty cycles, the machines and their operators are exposed to the risk of fire during every shift.
Fortunately, the use of high-quality, fire-fighting equipment, frequent professional service and regular training of personnel can mitigate this risk. In fact, the U.S. National Institute for Occupational Safety and Health statistics show that fire losses in North America have been declining as a result of improvements to system design, vehicle service practices and fire-safety training.
Complacency can be extremely costly, however, with lives, valuable assets and production continuity on the line. And, with insurance companies increasingly aware of these risks, securing adequate insurance coverage can be more expensive and harder to find.
Understanding why vehicle fires start
Most mining vehicle fires start when hydraulic fluid, lubricating oil or diesel fuel is ignited by a hot surface or electrical discharge in an oxygen-rich atmosphere.
By examining these potential fire scenarios in more detail, we can determine that the majority of fires are caused when pressurized hydraulic fluid leaks onto high-temperature surfaces, such as exhaust manifolds and turbo chargers. This type of fire is particularly dangerous, as fuel can continue to flow due to residual system pressure, even after the vehicle ignition is turned off.
Hydrocarbon fires can also occur when hydraulic fluid, fuel or lubricating oil leaks cause a build up of residue on internal surfaces on the vehicle. For example, when installed, a belly pan or sump guard can collect fluid that can be easily ignited by sparks. Potential sources for spark ignition can include a chassis or pan in contact with rocks, electric arcing from electrical components (i.e. alternators) and damaged electrical wiring. Other flammable residue can build up on vehicles based on the type of service. This is a recurring challenge in coal-mining operations.
These types of fires generally begin in areas that the vehicle operator can’t see, making the situation more dangerous. A fire can quickly escalate into a deadly situation for both the vehicle operator and equipment.
Prevention is key
The installation of an automatic fire-fighting system on a vehicle is an effective strategy to reduce the risk of harm to personnel and damage to the vehicle. The fire-protection strategy must include a detailed hazard analysis that focuses on the sources of fuel, heat and potential ignition. Automatic fire-fighting systems comprise three main segments: detection, actuation/control and suppression elements.
• Detection: Protected areas are generally the engine(s), generators and hydraulic plant, but electrical service areas can also be protected. Detection devices range in sophistication and mode of operation, but dual-spectrum infrared detection is widely accepted as the fastest and most reliable methodology available. Fixed-rate compensated heat detectors, such as Detect-A-Fire units, are robust and quick acting and provide a cost-effective method of detection.
These units can be located throughout a protected area. Linear heat detection cable is another effective way to provide detection that can be installed in a continuous loop around a protected area. While not as fast acting as IR or thermal detectors, the cable can be used to cover highly irregular spaces with relative ease.
• Control and actuation: The control units should provide detailed system information on alphanumeric displays. Machine operators can then easily determine system readiness or identify system faults. The control units should be mounted for easy operator access, so that the display can be read and the controls can be reached. Manual releases should be located on the escape path from the vehicle, and consideration must be given to installing a ground-level releasing location on larger vehicles.
• Suppression: The location and number of nozzle and detection devices is also important. Nozzles are generally connected to the agent storage cylinders via hydraulic hoses. Their location is based on the system manufacturers’ published performance characteristics, as well as an evaluation of areas that require critical coverage.
With fires started by broken hydraulic lines, it’s best to use a wet chemical agent that can provide cooling, as well as rapid flame knockdown. Cooling equipment surfaces with a wet fire-suppression agent drastically reduces the likelihood of re-ignition. Wet chemical agents can be used as a primary system or as a secondary securement discharge coupled with a dry chemical discharge.
In addition to a fixed fire-suppression system, portable fire extinguishers form an integral part of the on-vehicle, fire-protection strategy. Units should be installed on the escape path from the operator cab to provide ready access. Once a fire-protection system strategy has been established, two critical elements must be combined to provide a robust fire-safety program: training and service/preventive maintenance.
Training and service
Training schedules should include regular, recurring sessions for site personnel and cover all aspects of site safety. Particular attention should be given to new personnel, temporary personnel and contractors. Fire safety should be included in training sessions, so that everyone working on and around mining equipment is aware of the location and operation of fire-safety equipment.
The fire-protection system manufacturer or authorized representative should always perform service and maintenance of installed systems. Service typically includes planned preventive maintenance, inspection and cleaning. Recommended service intervals vary depending on the equipment’s hours of operation or calendar period.
Keeping machines clean, identifying and fixing hydraulic or fuel-system leaks and ensuring electrical systems are properly insulated and mounted are key factors in helping to prevent a fire. Visual inspections prior to the start of every shift also provide valuable data. The condition of the fire-protection system should be verified during this inspection.
Electrical conditions must be checked visually on the control panel and the cylinder pressure confirmed visually by checking the contents gauge. Cartridge-operated units, however, don’t have this facility, since the main cylinder isn’t pressurized. In this case, the stored pressure reading is the best choice for determining system reliability and readiness.
Fire safety is a critical element of any mining safety program. Time and resources are required to make it effective. With knowledge and planning, clear and substantial risk reductions can be achieved in nearly any mining operation.
Luc Merredew is senior product marketing manager with U.S-based Kidde Fire Systems. For more information, visit www.kiddefiresystems.com.