New advances in firefighting technology give surface mine operators the capability to avoid getting burned—both physically and financially—by disastrous equipment fires
By Russell A. Carter, Managing Editor
Surface-mine fires are grim, expensive and sometimes terrifying reminders that no industrial enterprise employing huge mobile, rotary and fixed equipment that operates around the clock, involving constant maintenance activity and using a wide variety of flammable liquids and materials, can be complacent about safety in the workplace—whether that place is in a maintenance shop or in the cab of a haul truck, shovel or loader.
The mining industry generally receives passing marks for being cognizant of fire-related risks, and for making employees aware of those hazards. Nevertheless, fires still occur at frequent intervals at mines and plants, and in an era of high production demands, increasingly larger equipment types and more remote mine locations, almost any conflagration has the potential to cause significant disruption—even if it doesn’t involve worker injury or worse. Examples:
- In late December 2012, Randgold Resources reported that production at its Tongon gold mine in Cote d’Ivoire had been affected by a fire at the processing plant. The fire started during a planned shutdown for repairs to a mill cyclone feed pipe, and spread to other areas within the plant. Although the fire was extinguished without injuries to any workers, the plant’s cyclone clusters, flotation cells and blowers, along with infrastructure for both milling circuits, suffered damage.
CEO Mark Bristow said the company intended to have both milling circuits operational again within 10 days, with the damaged classification circuits operational within three to four weeks following receipt of spare parts. Repairs to the plant’s flash flotation circuit repairs were dependent on the lead time for replacement blowers. On January 21, 2013, Randgold said the plant was still about two weeks away from full operational status.
Due to the fire and other problems encountered earlier in the year, the company revised the mine’s 2012 production estimate down, from 285,000 oz to between 208,000 and 210,000 oz.
- In Alberta, Canada, one of the major oil sands producers experienced a rash of three fires in five months. A 2005 fire at another oil sands facility cut that producer’s output by 50% for eight months.
- In Victoria, Australia, the state’s occupational health and safety agency reported in late 2012 that there had been 23 incidents involving fires on mobile equipment since January 2010. Although the larger portion of these events involved underground mining equipment, there was a string of common causes that ran through the entire assortment of instances, according to the report. These common factors included:
- Failure to maintain integrity of pressurized hydraulic hoses, or keep hydraulic lines safely located away from heated surfaces;
- Oil leaking onto hot engine components;
- Failure to install hose types, transmission coolers, power train components and even tires that meet manufacturer’s requirements;
- Failure to isolate brake fluid lines from overheated brake friction material issues;
- Build-up of material between hoses and heated surfaces, allowing thermal conduction and ignition; and
- Frayed electrical connections.
It’s clear that faulty or postponed maintenance practices rank high on the list of potential causes of equipment and facility fires. As an additional example, another report from an Australian safety agency—this one from a New South Wales mine safety organization—described the case of an hydraulic excavator working on overburden at a surface mine; a haul truck driver passing by noticed flames in the excavator engine bay and alerted the excavator operator by radio. The fire erupted from the engine bay, momentarily engulfing the excavator cabin before subsiding to the engine bay where it continued to blaze. The operator escaped by jumping 3.5 m to the ground, but was not injured. Attempts to control the fire with handheld extinguishers were unsuccessful and the excavator was destroyed.
The machine, according to the report, was fairly new and appeared to be well-maintained, but was not fitted with an automatic fire suppression system. It was equipped with two 9-kg fire extinguishers, one located on the side of the engine bay and one located at the front of the excavator on the opposite side of the cabin. Neither extinguisher could be accessed to fight the fire.
Subsequent investigation by a consulting forensic fire investigator concluded that the fire originated from a cracked hydraulic oil filter housing that allowed oil to escape and ignite on contact with hot engine components. The aluminum housing was designed to be installed with a socket or box-end wrench, applied to a cast nut at the bottom of the housing. However, sharp-tool marks on the oil filter housing indicated that it was installed with a pipe wrench or similar tool and most likely had been over-tightened. The housing cracked at the location of the sharp-tool marks.
The report—in addition to offering a list of measures that can prevent or minimize hydraulic-system fires (see sidebar)—concluded that an automatic fire suppression system would probably have contained the fire at an early stage, and strongly suggested that such systems should be installed on all heavy mobile equipment operating at mines.
That recommendation would get vigorous endorsement from the leading suppliers of automatic fire-suppression systems to the mining industry, such as AFEX Systems, United Technologies’ Kidde Fire Systems subsidiary and Tyco Fire Protection Products (TFPP), for example. They stress the importance of automatic systems in preventing or minimizing asset damage, improving worker safety and avoiding calamitous economic losses from mine fires, whether in mobile equipment or fixed plant facilities—and each offers system options that can be configured for a wide range of environmental conditions and specific fire-suppression requirements.
Mike Stromberg, global product manager–vehicle systems for TFPP, told E&MJ that hydraulic system-related fires—in which fluid leaking or spraying from breaches in high pressure lines comes in contact with hot metal surfaces—are quite likely the most common type of fire encountered on mobile mining equipment. As far as frequency of occurrence per type of vehicle, he noted that, “Just because there are so many haul trucks used throughout the industry, we see more truck-related fires than anything else, but fires involving large hydraulic excavators tend to be more catastrophic.”
Somewhat surprisingly, there doesn’t seem to be a significant difference in the number of fires reported in older equipment as opposed to newer models, according to Stromberg. This can be attributed, at least partly, to new engine technology that involves higher fluid line pressures and increased operating temperatures.
Typically, fire suppression systems are bought and installed after the equipment sale, either through a dealer/distributor or directly by the mine. In recent years, Stromberg noted, equipment OEMs have begun consulting more frequently with system vendors “to make their equipment more fire-suppression ready. Some of the larger equipment types carry thousands of pounds of fire suppressant in tanks. We’re working with a major haul truck OEM, for example, to help them design deck layouts and support to accommodate these systems.”
The gamut of fire-protection packages includes pressurized dry-chemical systems, newer stand-alone aqueous-agent (liquid) systems that provide enhanced fire-suppression performance over broader temperature ranges, and twin-agent systems that combine dry and liquid agents. Each type of agent has specific advantages: dry chemical agents have quick flame-knockdown and suppression properties; twin agent systems also provide quick knockdown (from the dry chemical component) as well as cooling (from the liquid agent) to reduce surface temperatures of heated metal below the flash combustion point. Stand-alone liquid-agent systems offer simplified design/configuration and efficient performance in the proper application.
Stromberg said that TFPP had noticed a gradual trend toward selection of its Ansul LVS single-agent systems by its mining customers, but the specific application will dictate which type of system should be used; for example, dry chemical agents can be effective when ‘broadcast’ into the general area in which a fire is occurring, while stand-alone liquid agents work best when sprayed directly on burning surfaces.
TFPP’s current top-of-the-line fire suppression product for mine vehicles is the Ansul Liquid Vehicle System (LVS), which provides both fire suppression and cooling in a single agent. LVS’s ‘Wet Agent’ is a proprietary blend of organic and inorganic salts; incorporated into this blend are the properties associated with conventional Class B liquid foaming agents. Wet Agent, when sprayed into a fire, interrupts the chemical reaction that supports combustion. Because the agent is liquid, it can flow into areas in which flammable liquids can settle. The water content of Wet Agent cools the fuel and surrounding super-heated surfaces, minimizing the chance for re-ignition. Wet Agent also forms a film over flammable fuels, which minimizes re-flash potential.
LVS system configurations include four-nozzle, 5-gallon; 10-nozzle, 15-gallon; and 20-nozzle, 30-gallon arrangements. Straight-line, split tee and manifold block distribution hose network options are also available. Pre-mixed agent containers and external pressure cartridges allow quick recharges, reducing equipment downtime. The LVS Wet Agent itself has a 25-year shelf life.
LVS’s fire suppression and cooling capabilities, along with additional security features operate within a temperature range of -40°F to 140°F (-40°C to 60°C).
With an eye toward the industry’s trend to locate mines in increasingly remote or undeveloped sites—and the attendant need to monitor and maintain fire suppression systems on mobile equipment at those mines—TFPP is currently developing a new generation of fire detection and activation technology which, according to Stromberg, will be fully electronically supervised. The generation beyond that, he explained, will also be integrated into the vehicle’s onboard machine health monitoring system, allowing fire-system events to be recorded and reported as part of the monitoring system’s data stream.
Kidde Fire Systems developed its new Sentinel system to provide a fully integrated fire protection solution for offroad vehicles. It offers the company’s Aqua Green XT wet chemical agent, has an operating temperature range of -40°F (-40°C) to 200°F (93°C), and is available with IP-66 and NEMA 4 type control packages, from cables to control panel enclosures.
Among its features intended to provide for convenient installation on a wide variety of vehicle types are pre-terminated ‘plug-and-play’ cabling that reduces installation time, increases reliability and helps prevent installation errors; flexible hose layout and nozzle coverage options that result in unobtrusive installations; and availability of unique control configurations that allow field programming of options including discharge and relay delays, as well as system power options that include self-contained battery operation. Also available is cylinder pressure supervision that provides real time response to a low pressure agent cylinder condition.
Additional benefits of the system, according to the company, range from superior IR detection technologies, which combines rapid response with high false alarm immunity; to field-programmable control panels with optional laptop interface, providing access to an available 4,000-event system log. Sentinel also offers a high degree of flexibility for dual discharge systems, with variable delay between discharges and relay contact operation.
Kidde’s Aquagreen XT, a foaming wet chemical agent designed for use on Class A and Class B fires, provides rapid flame knockdown and secures the hazard against the risk of re-ignition, according to the company. This is accomplished by two mechanisms: First, the foam creates a vapor-suppressing barrier that spreads across a liquid fuel separating the fuel from air. Second, with over 50% water content, the foaming agent also effectively cools surfaces as the heat is given up to vaporize the water. An additional benefit is that Aquagreen XT is also naturally freeze-protected as a result of a blend of certain additives; the use of salts negates the need for glycol as a freeze-point depressant. By employing this type of freeze-point depressant system, the fully biodegradable wet agent can offer an extremely low freezing point while still maintaining its fluidity at those very low temperatures.
Although these integrated fire protection systems offer immediate, on-the-spot fire suppression capabilities, they aren’t the answer to every mine-related fire event; and sometimes nontypical solutions can offer effective results as well. For example, when the time came for the Iron Ore Company of Canada (IOC) to acquire a new firefighting vehicle for its emergency response team, the company explored a new avenue in fire protection by selecting an Oshkosh Striker Aircraft Rescue and Fire Fighting (ARFF) vehicle from Oshkosh Corp., based in Wisconsin, USA.
“With the Oshkosh Striker, we’re blazing a new trail,” said Jamie Stagg, IOC Superintendent, Emergency Services and Security. “Our engineering team evaluated a wide range of traditional fire apparatus, including aerial ladders and platforms that can operate at heights. But when we considered our number one fire protection priority—the mine site itself, with its rugged road and no water supply—we decided to go with the Striker.”
The Striker’s large water-storage capacity, combined with its maneuverability and capability to operate at heights in and around the mining operations, make it uniquely qualified for this application. As aircraft firefighting vehicles, Strikers are specifically designed to perform under demanding conditions, featuring proprietary technologies such as the Oshkosh TAK-4 independent suspension system, Snozzle high-reach extendable turret (HRET), and Command Zone advanced electronics for enhanced maneuverability, firefighting power and reliability.
The Striker on duty at IOC features a 17,034-liter (4,500-gallon) water tank, a Snozzle HRET, a foam system, a dry chemical system, a structural firefighting package (with pre-connected hand lines), and a robust winterization system for temperatures that can plummet to -40ºF.
The Striker also is equipped with the Eagle Eye Driver’s Enhanced Vision System (DEVS) that combines a moving map display with an infrared thermal imager for better visibility and situational awareness in poor conditions. In addition, the Eagle Eye system, through its wireless data link, allows for critical information exchange in real time between the Striker’s crew and its command center for efficient communications during an emergency.
“Around our processing plants, the roads are paved and have accessible fire hydrants, but then you transition to eight kilometers of gravel roads to reach the mine site,” said Stagg. “In the springtime, when the winter snows thaw, those gravel roads in and around the mine can be slippery and difficult to navigate. With rough terrain and 320-ton haul trucks [at the mine], the Snozzle will allow us to quickly respond to any type of emergency while keeping our Emergency Services and Security team out of the line of fire. That’s why we believe the Striker is the ideal truck for our application.”