Mine Fire Safety

The United States Department of Labour’s Mine Safety and Health Administration points out that safety and health in the mining industry has made significant strides during the 20th century, and over the last 25 years in particular. However, mining remains an inherently high risk environment where the impact of a fire can have catastrophic consequences.

Challenges abound above and below ground.
According to the National Institute for Occupational Safety and Health (NIOSH) electrical shorts and equipment malfunctions are among the leading causes of US mine fires. From 1990 to 2007, there were 1601 reportable fires that occurred in the US mining industry – an average of 89 fires a year. So, the fact that mine fires are occurring with alarming regularity reinforces the importance of recognising and eliminating the potential hazards.
While over the years the main working areas below ground have undergone any number of health and safety improvements, the same cannot always be claimed for some of the equipment used in mines that has the very real potential to catch fire, triggering a major blaze.

Much of this equipment is housed in cabinets or enclosures – often referred to as “micro-environments” – and includes cabinets housing essential electrical control equipment, many of which may well be essential to miners’ life preservation. However, mines typically have a host of other “micro-environment” fire safety challenges. These range from emergency lighting installations to essential-power cabling installations, generators, batteries and UPS equipment, conveyors, lifts, control rooms, sub-stations and fuel stores.
Hardly surprising then that NIOSH’s Office of Mine Safety and Health Research Fire Fighting and Prevention concludes that: “fire detection is a critical component in the safety of underground mines.”

The Blind Faith Trap
Blind faith – a belief without true understanding, perception, or discrimination – should have no place to thrive when it comes to mine safety. Unfortunately, it is an easy state of mind to slip into, particularly in an environment where safety in general is seen as a top-of-the-agenda priority. It is easy to believe, for example, that once installed, a fire suppression system can be endlessly relied upon to work without any means of assessing its readiness on a daily basis. Worse, emergency response training, important and commendable though it is, can foster a mistaken belief that a seemingly small fire in a cabinet, enclosure or compartment would soon be spotted, contained and dealt with. Sadly, history is littered with instances where the consequences of this mistaken belief have been measured in lives lost and assets destroyed.

The reality is that many infernos start as a small fire that, left unattended – often for an alarmingly short space of time –will develop into a major conflagration.
Above ground, the main fire safety challenge is to be found in among the heavy plant and machinery engine compartments and breaking systems, and so are where investment in fire safety measures are most likely to have the greatest impact and payback. According to the findings of the United States Department of Homeland Security’s National Fire Incident Reporting System and the country’s National Fire Protection Association, mechanical and electrical failures or malfunctions account for the majority of fires in off-highway equipment, with one of the most common locations for the outbreak of a fire being in or around the engine compartment.
The only truly effective solution is to provide each of these “micro-environments” – above and below ground – with dedicated, intrinsically-safe, risk-specific fire detection and suppression. This calls for the use of tried-and-tested technology that is completely self-contained, requires no external power source, is not affected by atmospheric contamination, and can withstand the punishing working environment.

The Underground Fire Threat
Çayeli is an underground copper and zinc mine located in Rize on the Black Sea coast of north- eastern Turkey, employing over 450 with a further 159 contractors on site. It is one of the largest copper reserves in Turkey and mills 3,000 tonnes of ore a day.
The main “enclosed” fire risks were identified by the mine’s management as being the underground mud pumps and electrical cabinets and, to ensure that adequate fire protection was provided, the company drew up a checklist of essential features. This included:

•  The need to provide 100 percent response reliability.
• The ability to stop a fire precisely where it breaks out, before it has any opportunity to take hold and spread.
• Being unaffected by vibration or the heavily dust-laden underground environment, debris and airflow.
• Provide around-the-clock, unsupervised protection.
• Not require external electrical or other power that has the potential to fail and so put the system out of operation.
• Being intrinsically safe to match the high standards of safety required in the mining industry.

Following detailed consideration of several potential solutions, it became apparent that a number of other features had to be added to the original list of requirements. These included the advisability of the solution being a fully integrated fire detection and fire suppression package; one that used a fire suppressant agent appropriate to the particular fire hazard and the equipment being protected. To ensure continued operation of
the mine following a fire, the importance was recognised of choosing a solution that utilised a suppression agent that, when discharged, would not damage the equipment it is there to protect. Avoidance of time-consuming clean-up operations was also seen as critically important to getting the mine back into operation following a fire.

The Mine Vehicle Fire Risk
The management of the Assarel-Medet JSC mine in Bulgaria reached similar conclusions when seeking to protect its heavy ore-moving crawler equipment. However, to this list of essential features, the company added that the solution must be able to contend with the wide temperature variations experienced in Bulgaria, where in winter it can drop as low as –5°C, while summer temperatures can be as high as 28°C. It was also deemed important that the solution should not jeopardise the operation or maintenance of the equipment it is protecting, or demand excessive space for suppressant storage, as space within the crawler’s engine compartment is very limited.
Assarel-Medet JSC is the country’s largest open-pit copper mining and processing company, producing around 200,000 tons of natural copper concentrate every year and processing in the region of 13 million tonnes of copper – more than half of the country’s copper output. Located in the Sashtinska Sredna Gora Mountains, north-west from the town of Panagyurishte and 90 kilometres east of Bulgaria’s, Sofia, its operations cover an area of 20,000 acres at an average altitude of 1000 metres.

So, understandably, the loss or serious damage of one of these giant machines resulting from an engine fire would seriously jeopardise production schedules, possibly for many months while the crawler was repaired or even replaced at the cost hundreds of thousands of dollars. An uncontrolled engine fire also places the equipment operator at risk of serious of injury or death.
However, the precise nature of the fire hazard that these crawler vehicles present had to be carefully considered if the detection and suppression solution was to offer the maximum protection. In addition to the crawler’s fuel and the risk of fuel line ruptures, this meant taking into account any number of flammable liquids present throughout the engine compartment. These include hydraulic, brake, automatic transmission and power steering fluids, along with combustible accumulated grease on the engine block, for which frayed or damaged electrical wiring can easily provide the ignition source.

The dynamics of the airflow in and around a crawler’s engine compartment when it is in motion was another factor; it has the potential to seriously impair the performance and reliability of traditional detection and suppression systems. This is because heat and flame typically rise from the source of a fire and may, when the crawler is moving, be propelled elsewhere. The inevitable build-up of dirt in and around the engine, intense temperature variations and vibration are also factors that are known to cause traditional detection and suppression systems to fail to provide the necessary fast and accurate fire detection and suppression.
This inevitably led to several potential solutions being dismissed by Assarel-Medet, including those that either were solely detection or solely suppression, and not an integrated solution.

Integrated Detection and Suppression
In both cases, at the Çayeli mine in Turkey and the Assarel-Medet JSC mine in Bulgaria, the decision was taken to opt for a tube-based fire detection and suppression system and, after careful research, both selected US-based Firetrace International’s Firetrace system that is today safeguarding 150,000 installations around the world. Each of the Firetrace systems comprises an extinguishing agent cylinder that is attached to proprietary Firetrace Detection Tubing. This is purpose-developed leak-resistant tubing that at the Çayeli mine is snaked throughout the cabinets and mud pump enclosures, and that at the Assarel-Medet JSC mine is threaded throughout the crawlers’ engine compartment.
Heat or flame will immediately cause this tube to rupture and the suppression agent is automatically released, extinguishing the fire precisely where it starts and before it can take hold. An important consideration for both mines’ managements was that, unlike many of the other suppression systems evaluated, Firetrace can only ever be activated by a real fire, so there is no prospect of false alarms or unnecessary agent discharge that might otherwise curtail mining operations. Significantly, it is the only UL [Underwriters Laboratories] listed, FM [Factory Mutual] approved and CE [Conformité Européene or European Conformity] marked tube-operated system in the world that is tested as an automatic fire detection and suppression system.

The Çayeli underground project uses both the Firetrace Direct System and the Firetrace Indirect System. In the Direct System, the Firetrace Detection Tubing performs a dual function; it is both the detection device and the suppressant delivery system, whereas the Indirect System uses the tubing as a detection and system activation device, but not for the agent discharge. The rupturing of the chemical-resistant tube results in a drop of pressure that causes the system’s indirect valve to activate. This diverts flow from the detection tube, and the agent is discharged from the cylinder through diffuser nozzles, flooding the entire enclosure.
A pressure gauge on the cylinder allows quick and easy checks to be made to ensure that the system is always operational.

Suppressant Agent Selection
The choice of suppression agent was critical for both mines. Two risk-specific suppression agents were chosen for the Çayeli mine project – ABC dry chemical powder is safeguarding the mud pump enclosures, while 3M Novec1230 Fire Protection Fluid is being used to protect the mine’s electrical cabinets. The Assarel-Medet crawlers, which utilise just the Firetrace Direct System, are also using ABC dry chemical powder.
ABC powder insulates Class A fires – those involving freely burning materials such as wood, paper, textiles and other carbonaceous materials – by melting at between 182°C and 205°C. The powder also breaks the chain reaction of Class B and Class C (Class B in the USA) fires – those involving flammable liquids such as petrol, diesel, solvents, lubricants and spirits, and flammable gases such as butane and propane – by coating the surface to which it is applied.
Another advantage of using ABC powder in these applications is that, on discharge, it leaves a residue that absorbs flammable liquids, helping to avoid re-ignition. The particles of powder are too large to penetrate engine air filters and so only the exposed external engine surfaces will need to be cleaned after a system discharge, by wiping, vacuuming, or washing.
3M Novec1230 Fire Protection Fluid is the latest clean-agent suppressant, one that quickly knocks down Class A, B and C fires with no risk of thermal shock damage to delicate electrical equipment. It is electrically non-conductive and non-corrosive and leaves no oily residue so clean-up operations are unnecessary following a suppressant discharge. It is stored as a low-vapour-pressure fluid that, when discharged, transmutes into a colourless and odourless gas, using a concentration of the fluid that is well below the agent’s saturation or condensation level.

Scott Starr is director of Marketing at Firetrace International

For further information, go to www.firetrace.com