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BELT CONVEYORS IN UNDERGOUND MINES

Published

2020

Wed

29

Jul

 

 

 

ASSESSMENT AND EFFECTIVE MANAGEMENT OF RISK

BELT CONVEYORS IN UNDERGOUND MINES

By Eugene Pretorius

 

A Risk Assessment on the belt conveyors in the underground metal and no-metal mines was conducted. The objective of the exercise was to determine the inherent fire risks on conveyors, to summarize the findings and make firm recommendations to contribute towards the successful management of risk.

 

We concentrated our efforts on fire, which may have a negative influence on life safety. The assessment entails the relative danger of the start and spread of fire; the generation of smoke, gases, or toxic fumes, and the possibility of explosion or other occurrence endangering the lives and safety of personnel or causing significant damage to property.

 

Risk control measures and the effectiveness were evaluated against national and international codes of standard and statistics, pertaining to fire prevention of this particular type of risk.

 

Extensive research was conducted, and various documents and codes of practice have been used to assist in the conclusions reached in the assessment.

 

The report deals with an entire strategy to reduce the risk

 

Conveyor belts are extensively used to transport bulk solids in underground mines. The belts contain

polymeric materials and can present a serious hazard in terms of rapid fire spread and generation of

toxic, corrosive smoke.

 

Associated equipment includes motors, support structures, rollers and belting. Belts may be several

meters wide and vary in length from a few to several hundred meters.

 

The source of a fire could be electrical, friction and/or overheating. If there is severe friction and protection fails to work effectively enough heat could be produced to ignite the belt.

 

The conveyors are located underground, and any fumes produced during combustion could be carried to the working places endangering the health (and lives) of workers underground. Equipment above, below, adjacent to and alongside the conveyors could also be damaged (electrical cables / services, etc.) and cause business interruption.

 

EVALUATION OF THE RISKS

 

External influences

Utilities such as plastic-coated electric cables in trays or service lines may be carried in conveyor tunnels or housings. These can contribute to fire spread and severity and further contribute to production interruption.

 

Fire Extinguishment complications

Conveyor systems located underground do not lend themselves to direct access for manual firefighting.

 

In an underground mine fire control is not sufficient and fire extinguishment is essential for the

following reasons:

 

  • As long as fire burns, even if it does not grow in intensity or area and appears to be responsive to fire control, toxic smoke and fire gases are produced that can endanger persons in the mine.
  • Water supplies are limited in many underground mines. Fire control, therefore, should be considered temporary, because the fire will grow immediately to maximum intensity when the water supply is depleted.
  • Routing of water lines has caused severe problems in fighting fires at some large mines. If a fire occurs in an area of opposite airflow, the fire has to be approached in the same direction as the airflow, but the water flow is moving through the fire area. Usually water lines in a fire area are damaged or broken by falling sections of burning roof. When a water line breaks in this situation, the fire fighters are without water, and direct fire fighting is no longer possible.

 

Even in situations where air and water are flowing in the same direction, the water lines or hydrants in a burning entry are likely to be broken by the falling sections of a burning roof. In this situation, a planes shutdown of the water line should be undertaken as soon as possible in order to install a multiple hydrant in the water line at a convenient location close to the fire.

 

With the multiple hydrant in place, at least three fire hoses can be served effectively from the water line

 

  • Mines that obtain their water supply from an underground source can also have this problem of opposite directions of airflow and water flow. Usually there is no sure solution except to provide an alternative source of water or a large storage of water on the surface.
  • If the power for the pumps is fed from the high-voltage system that feeds the mine and the fire damages the high-voltage cable anywhere in the system, the power can trip the entire system and shut down the pumps. Coordination of the electrical protective equipment, or even a separate power supply might be needed to ensure that the pumps continue to supply water for fire fighting.

 

Because of the many factors that should guide the choice of location of water lines and hydrants, the water supply and ability of hire hose streams to reach a fire at any location or entry served by the water line should be the criteria by which the location is chosen.

 

Other Services affected

The main air, water, electrical power and communications lines can all be located in the conveyorway. The fire can cause a belt to break and strike any of these. The heat from a fire has been known to sever power lines, including the supply to the main fresh air fans on the surface. This can disrupt the mine ventilation system and permit contamination of much of the mine.

 

Test Methods for conveyors

Fire test specification is one of the requirements to determine the ‘fire-resistant’ ability of conveyor belts. There are various fire test procedures available to evaluate the fire-resistant properties e.g. drum friction test, spirit burner flame test and high-energy propane burner test.

 

The propane burner test is required for countries such as Canada, UK, India and also Australia. Germany (DMT) and the Unites States of America (MSHA) have different test requirements. It must be stressed that the propane burner test is not a South African requirement at present and must therefore not be interpreted in this manner. It is somewhat worrying though, that the South African standards are not in accordance with other international practices.

 

In the BCS specification (fire test requirements), the high-energy propane test is one of the requirements apart from the Drum friction test and the spirit burner flame test. The last two tests can be carried out in South Africa through the SABS.

 

According to SABS document SABS 971-1980, the drum friction test and ISO 340 for flame resistance of conveyor belts testing, is required.

 

The BCS standard is more stringent. There are different test protocols for testing compliance of belts according to the NIOSH/MSHA testing methods against the BCS test method. However, some results showed ambiguous conclusions, meaning some belts which passed the BCS have failed the MSHA tests and others which failed the BCS tests have passed the MSHA tests.

 

The High Energy Propane Burner Test (Gallery) is an extremely aggressive procedure and is used in the UK almost exclusively for solid woven PVC and PVC/Nitrile conveyor belting. PVC and PVC/Nitrile belting are the only types approved for use underground in the UK and this has been the case for approximately the past 30 years. The reason for this is the PVC and or PVC Nitrile conveyor belting have proven to be the only commercially viable types capable of meeting the requirement is BCS 158- 1989 with regard to Fire Performance (Gallery testing).

 

The BCS 158-1989, Section 1015.2 (Spirit burner flame test) is similar to SABS 971-1980, Section 6.13 (Flame resistance) test.

 

Some belts are compounded with fire retardant additives and are advertised as meeting certain codes, such as those specified by the U.S. Bureau of Mines (USBM) and the National Coal Board of England (NCB). These fire-retardant belts have to pass certain restrictive tests to determine ease of ignition and ability to spread a fire from point of ignition. However, these regulatory tests do not simulate all conditions that may be found in a conveyor system such as incline, stacking, and presence of contributory combustibles. Further, USBM and NCE regulations only apply to underground coalmines. There are no corresponding regulations on the combustibility of conveyor belts in other mining occupancies or aboveground industries.

 

Conveyor belts, whether made of natural or synthetic rubber or plastics, are generally assumed to be capable of self sustained fire propagation regardless of the presence of other combustibles. Because belts are frequently changed and substitutions made, fire retardancy of the belt should generally not be given consideration unless it can be demonstrated that the belt used, and replacement belts are the same.

 

In the same few years there have been incidents in Australia and the USA wherein approved belts have been involved in major underground fires. Such incidents have raised questions about the suitability of current standard fire tests to properly distinguish between belts that will and will not propagate a fire.

 

Inherent Fire Protection Problems

Automatic detection systems and automatic sprinkler systems in mining facilities need to be specifically addressed for the following reasons:

 

  • The content of a mine occupancy is continually changing. Most items are not fixed and are designed to be moved with the mining operation. A mine operates as a heavy-duty excavation construction site and, thus, has the same transitory nature as a construction site.
  • Unlike aboveground industrial occupancies, great distances are not unusual within an underground mine.
  • Mines have extremely harsh and unusual environments compared to aboveground industrial occupancies. Heavy concentrations of combustible dusts (in the case of coal mines), the presence of explosive gases, temperature extremes, saturated humidity conditions, standing water, unstable strata, roof-to-floor heights that vary from 71cm to 6.1m, and complex ventilation systems are all commonplace. The possibility of abuse from heavy machinery is a common hazard.
  • Mining occupancies exhibit unique physical characteristics not found in any other type of occupancy. One example is the extreme pressures that can occur in a water line.
  • Mines employ specialized facilities, equipment, and production processes that are not utilized in other industries. Fire protection efforts that fail to consider the unusual operating characteristics and fire protection requirements of underground mining systems could result in non-optimal protection or the inadvertent introduction of hazards.
  • Although the conveyed product and the structure may be non-combustible, loss history demonstrates that the belt itself presents a sufficient combustible loading to spread the fire without other fuel contribution.

 

Smoke toxicity and Ventilation

Burning belts generate large quantities of smoke, and vision is severely impaired. The smoke characteristics, including concentration, particle diameter and optical density of smoke on burning belts can vary significantly depending on the type of belting and ventilation rate. In tests conducted the CO and CO2 concentrations and O2 depletion were always greater at the lower airflows.

 

When conveyor belts (neoprene, polyvinyl chloride and styrene-butadiene rubber) are subjected to thermal oxidative degradation about 70 different compounds are identified in the volatile thermooxidative products.

 

Hydrogen chloride is the major toxic product formed, accompanied by relatively low quantities of carbon dioxide, carbon monoxide, Sulphur dioxide, benzene, chloroprene, cresols, chloroethanol, formic acid and C8 hydrocarbons.

 

The increased toxicity of the fumes generated during combustion of fire-resistant conveyor belts is not addressed in any standards. Mining companies using these belts are not fully aware of this hazard. The use of fire-retardant conveyor belts with their inherent high toxicity level of fumes generated during burning should not negate any fire prevention, detection and suppression measure commonly used for ordinary conveyor belts.

 

The possibility of the fire causing highly complex ventilation disturbances such as throttling or reversals also exists. Such disturbances can be extremely difficult to predict but can affect mine evacuations and firefighting profoundly by causing the contamination of airways through to be safe.

 

FIRE TESTS CONDUCTED

 

Effect of ventilation on conveyor belt fires

  • The Bureau of Mines, U S Department of the Interior conducted full-scale fire tests of conveyor belts to determine the effect of airflows of 1,5 m/s and 4,1 m/s on the fire development and propagation.

 

In essence the tests revealed

 

Three different styrene butadiene rubber belts were ignited and completed burned at both airflow rates.

 

The flame spread rates, downstream gas temperatures, and CO and CO2 concentrations for each belt were less at the 4,1 m/s that at the 1,5 m/s airflow.

 

Two PVC belts burned at the lover airflow with rapid flame spread rates, but, at the higher airflow the same belts did not propagate flame and damage was limited to the ignition region. A PVC belt and a chloroprene rubber belt did not burn at either airflow. These overall results indicate that for these test condition, the high airflow reduced the hazards of propagating conveyor belt fires.

 

Where flames did not propagate down the sample, the maximum values occurred during the tray fire and burning of the belting in the ignition area. A comparison of the value for the same belt shows a lower temperature for the higher airflow in all cases. This lower temperature is consistent with the slower flame spread rate and the increased ventilation flow that results in more mixing and cooling of the combustion gases.

 

The belt temperature necessary to propagate a belt fire will vary with the composition of the belt and the generation rate of combustible decomposition products.

  • Fire resistance versus non-fire-resistant belts in the same tests revealed:

 

Non fire-resistant rubber belt

 

At the 1,5 m/s flow, flames flashed over the top surface of the 9,1 m belt sample about 1 min after ignition of the tray fire. The rapid flame spread rate was about 7,6 m/min. The entire sample then burned in an intense fire that consumed the belting in a bout 15 min. At the 4,1 m/s flow, the belt sample ignited and was consumed by a steadily advancing flame front with a flame spread rate of 0,7 m/min. The belt fire lasted about 30 min after the start of the tray fire. The flame spread rate was about 10 times greater at the lower airflow of 1,5 m/s that at the higher airflow of 4,1 m/s. The flame spread rate of this belt at the 1,5 m/s flow was also much greater than those of the fire-resistant styrene butadiene rubber belting.

 

Conveyor fires in Canada

Fires associated with conveyors have long been recognized as a serious hazard in underground coal mines. Recently, however, there have been some significant conveyor fires in Canadian underground hard rock mines. This offers important evidence as to the nature and causes of potential hard rock mine fires. There also warrants attention with a view to improving overall mine design, ventilation and emergency preparedness. This paper was motivated by the need to understand the causes and mechanisms of conveyor fires in order to improve their safety. This should be possible through implementing more effective monitoring systems, as well as improving conveyor designs.

 

American Experience

The Unites States Bureau of Mines (USBM) reported that for the period 1950 to 1977, that the belt head area was there a conveyor belt fire seems most likely to start, where most ignition sources are located. Other possible hazards, however, can exist anywhere along the conveyor belt, such as stuck rollers that can become heated by friction with the belt. Belt misalignment can also be a problem, where the edge of the belt might rub against a support member. This could result in the support member becoming red-hot and the belt edge also becoming frayed.

 

British experience

An analysis of 113 conveyor fires in underground British coal mines showed that 41 originated at the driving pulleys, 32 at defective rollers, and 40 elsewhere on the conveyor system. The potential severity of such fire which can spread along conveyor roadways is illustrated clearly by the disaster at the Creswell Colliery in Britain in 1950 when 80 men were overcome and killed y toxic fumes from the fire. The fire started from smoldering caused by friction, and developed into a flaming combustion, propagating along the roadway for a total distance of 650m.

 

Canadian Experience

Although few underground conveyor fires are experienced in Canada, recent cases of conveyor fires indicate that they can still pose serious safety, production and financial risk.

 

The Mines Accident Prevention Association of Ontario (MAPAO) Underground Equipment Committee reported in 1987 on fires on underground conveyor systems used for transportation of noncombustible material in Ontario. In summary, 83 percent of fires originated at the head pulley of the conveyor systems. Forty-two percent could have been avoided, had a zero-speed switch been installed or been in good working order. Twenty-fiver percent of these could be directly linked to a poor maintenance program. Torn belts caused seventeen percent of fires. Most of the conveyor fires were caused by friction.

 

The of the reported 12 fires during this period, originated at the head pulley of the conveyor system.

 

This led the committee to conclude that the main effort for the fire prevention, detection and suppression should be concentrated at the head pulley of the conveyor systems designed for handling non-combustible materials.

 

General

In many cases, such fires propagated through hundreds of meters of conveyor-way. In addition to injury and loss of life they resulted in significant costs and production losses. Some of these fire involved rubber belts, while other involved polyvinyl chloride and neoprene belts that were classified as “fire resistance”.

 

In order to minimize the hazard of belt fires, the U.S. Code of Federal Regulations for underground coal mines requires: (U.S. Code of Federal Regulations, Part 75, 1988)

1.   approved fire-resistant belting,

2.   automatic fire suppression systems for belt conveyor drive areas,

3.   automatic fire sensor and warning device systems along belt haulage ways,

4.   waterlines installed parallel to the entire length of belt conveyors,

5.   belt slippage and sequence switches, and

6.   special ventilation requirements along belt haulage entries.

 

In retrospect the Conveyors Code of Federal Regulations, (Title 30, Volume 1, Parts 1 to 199), (Revised as of July1, 1997) for Underground metal and non-metal mines stipulate:

 

Subpart C - Fire Prevention and Control Sec. 57.4263 Underground Belt conveyors.

 

“Fire protection shall be provided at the head, tail, drive, and take-up pulleys of underground belt conveyors. Provision shall be made for extinguishing fires along the beltline. Fire protection shall be of a type, size, and quantity that can extinguish fires of any class in their early stages which could occur as a result of the fire hazards present”.

 

Subpart C – Fire Prevention and Control Sec 57.4503 Conveyor Belt slippage

 

  1. “Surface belt conveyors within confined areas where evacuation would be restricted in the event of a fire resulting from belt-spillage shall be equipped with a detection system capable of automatically stopping the drive pulley”
  2. “Underground belt conveyors shall be equipped with a detection system capable of automatically stopping the drive pulley if slippage could cause ignition of the belt”
  3. “A person shall attend the belt at the drive pulley when it is necessary to operate the conveyor while temporarily bypassing the automatic function”.

 

Mechanisms of Belt Ignition

 

Drive Pulley

Dutch studies were made to investigate the ignition of a stationary belt on a moving drive pulley. It was concluded that: “The thicker the rubber belt, the lower the velocity of air, and the lower the tension on the belt, the smaller was the risk of fire”.

 

In British tests, also with a stationary belt, the temperature of the belt rose to 500oC the broke. It was inferred that all qualities of belt will flame but that invariably, ignition originates in the cotton fabric after the rubber cover has been worn away.

 

In French tests two pieces of belting were used, one was new, and the other worn out. The test confirmed that: “Ignition of the belt is produced through the agency of the fabric, which ignites after the cover has worn off. It is therefore the rate of wear surface that determines the length of time necessary to ignite a slipping belt on the drive pulley”.

 

Idler Rollers

Overheating of idler rollers would occur when the bearings in the roller arm seize, jamming the normally free-wheeling roller. As long as the conveyor system operates, the belt will not absorb an adequate amount of energy during each pass over the seized roller to ignite. When the conveyor is stopped, if the heat transferred from the roller is sufficient to raise the temperature of the conveyor belt or surrounding coal or other combustible to its ignition temperature, then a fire might result.

 

Factory Mutual Standards and Tests

Ventilation (air flow) within a sprinklered tunnel or gallery does not appear to influence fire spread to a great degree.

 

factory Mutual Research conducted airflow studies over conveyors in coalmines to test detector sensitivity. These tests were correlated to sprinkler operation after detection by computer simulation. For low airflow (50 ft/min [15m/sec]) the simulation showed that one head would have limited further spread. For moderate air velocity (300 ft/min [91 m/min]) who sprinklers limited further spread. For very high airflow (700 ft/min [213 m/min]), the simulation showed that one head theoretically, could stop flame propagation. It became apparent that airflow, under sprinklered conditions, does not greatly contribute to fire spread and that under very high flow rates, airflow may actually cool the fire. Because conveyor belts have relatively low burning characteristics, sprinklers are very effective in gaining early control before airflow becomes a major contributor. However, where sprinklers are lacking, high ventilation airflows may substantially influence fire spread.

 

Evaluating the Individual Conveyors

This assessment has been generic in nature and each conveyor on the mine should be assessed individually, as the risk will not be the same for all. Various factors will differentiate each of the conveyors.

 

Treatment and Control of the Risk

There are a significant number of possible solutions to control the risk to persons underground from a burning conveyor.

 

Listed below are a number of methods that can be used. The pro’s and cons of each are discussed.

 

Some may be regarded as too onerous, but they have been included for completeness.

 

Fire Prevention

In order to ensure that a fire will not occur, either the hazard (conveyors) or peril (ignition source) has to be removed. However, this is not possible.

 

Ignition Source Control

Belt alignment limit switches should be provided on conveyors to shut down belts that are improperly

tracking.

 

Motion-sensing switches should be provided to detect a slipping or jammed belt and be inter-locked to shut off driving power when the belt stops or slows down more than 20% of normal speed. In addition, provide shut-off power on contributing conveyors so that no operating conveyor can discharge material to a stopped downstream conveyor.

 

Protection against the effects of belt slip on the drive pulley may e obtained in several ways; Reduction of the risk of slip, control of slip, and temperature control. It is important, when fixing the critical percentage of slip, not to choose too low a value, for this would entail the risk of interruption in production. This percentage depends not only on the nature of the belt, but on the specific operating conditions of the conveyor.

 

Due to their numbers on any belt installation, monitoring of idler rollers for overheating is impeded. Install an economic identification system to monitor the overheating in individual idlers through an audible alarm.

 

Although not required, it is advisable that smoke or heat detection be provided over known or frequent ignition zones, such as conveyor drive pulleys and drums, to shut down the conveyor system and signal emergency response upon fire detection, even for non-propagating type conveyors. Compartment sizes and contours, airflow patterns, obstructions and other characteristics of the protected area shall determine the placement, type, sensitivity, and, where applicable, the number of detectors. From the examination of many different types of fire detectors, its becomes apparent that a practical system of conveyor fire detection must be capable of:

  • detecting the hazard at an early stage, when the overheating has not yet reached ignition point, and be reliable, with a minimum of false alarms, and preferably be able to self-diagnose for any fault in the system;
  • continuous operation, 24 hours, seven days a week;
  • remote operation, with an indication of alarms, both locally and on the surface; and simplicity in operation and maintenance, with the fire indication and procedures well understood by responsible staff.
  • Preventative maintenance programs should be developed to reduce the potential of other commo ignition sources such as friction, overheated bearings or drive machinery, misalignment of belts or drivers, etc.

 

Electrical Protection

Where electrical protection is installed it should be maintained according to standards. The chance of a fault being sustained for long enough to cause a fire is extremely remote. The ignition source can be removed.

 

The identification of hot connections is worthwhile, and the use of Thermographic cameras is recommended on a six-monthly basis.

 

Fire Control

Ventilation Control

Separate airways should be provided to handle all main airflow both from and to the surface, leaving the operating shafts basically neutral. This greatly improves the plans for control in the event of an underground fire.

 

Ensure the ventilation systems are capable of extracting the correct volumes of air, based on typical conveyor fire growth toxic gas volumes. The U.S. Bureau of Mines has developed a computer simulation program that can be used to analyze the spread of combustion products by a mine ventilation system. Information on this program, including instructions for obtaining a free copy, are provided in U.S. Bureau of Mines Information Circular 9245. “A User’s Manual for MFIRE: A Computer Simulation Program for Min Ventilation and Fire Modelling”

 

Fire Suppression Systems

Install fire suppression systems. As the actual incidence of belt fires is low in underground mines, and most of these are in the area of the belt drive and the belt take-up, protection of only the area from the discharge pulley to the end of the take-up is advised. If the belt structure contains a deck between upper and lower stands of the belt, automatic sprinklers should e located beneath the deck.

 

Emergency Plans

It should be recognized that electrical maintenance personnel have the potential to make a very important contribution in the emergency situations that are most likely to occur. However, most such situations will also involve other disciplines, such as operating personnel. An overall emergency procedure for each anticipated emergency situation should be developed by each discipline involved, detailing responsibilities. The procedure should then be run periodically as an emergency drill.

 

It is vital that an emergency plan is drawn up for main underground conveyors covering the following issues:

  • evacuation of persons if necessary
  • extinguishing of the remainder of the fire
  • preventing smoke from reaching the workings
  • re-establishing power to the exhaust fans
  • replacement of conveyors and repairs to other services

 

Fire hydrants

Hydrants should be located to ensure that fire hose can be laid quickly from hydrants, which are located on the water line in any of the entries, through crosscuts to a fire located in parallel entries, diagonals or crosscuts, rather than being located for convenient use in the entry where the water line is located.

 

Fire hose requires special consideration at mines. Cotton or linen-lined jacketed hose should not be used, as they are subject to mildew attack. Even mildew-treated hose does not endure. Rubber-lined and rubber-jacketed hose resists mildew attack, but this type of hose is heavy, stiff, and expensive. Neoprene-lined polyester hos with rick lug couplings is probably the best hose for mine use. The pins of pin-type couplings are easily broken or knocked off, and their use should be avoided.

 

many mines have standardized on 3.8 cm fire hose, even though their water lines can supply substantially more water than is required to get proper discharge from a 3.8 cm hose nozzle.

 

While the total water flow of two 3.8 cm hose lines is about the same as one (6.4 cm) hose line, our opinion is that, two 3.8 cm hose lines provide greater flexibility during a firefighting operation.

 

Conclusions

  • The risk of a conveyor fire is low, and with good electrical protection, it can be reduced further
  • The mine ventilation and emergency preparedness systems should be planned to be able readily, to isolate and combat any conveyor fire
  • Draw up and implement a comprehensive maintenance and inspection plan
  • Draw up and train necessary persons in emergency plans
  • Fire water reticulation systems play a vital role in effective manual fire suppression evolutions and these should be controlled by one body which has the technical ability and know-how. Substandard contractors should not be used for these critical installations
  • The mine operator or the mine operator’s designee should perform a fire risk assessment for all conveyors. This analysis shall include evaluation of the risk potential for the start and spread of a fire and the generation and spread of smoke, gases, or toxic fumes that could endanger the lives and safety of personnel or cause unacceptable damage to property
  • If the risk analysis discloses (as described in 2.8) unacceptable risks, further assessment shall include an evaluation of each of the following:

1. Methods for minimizing or eliminating existing hazardous fire conditions

2. Use of detection and early fire warning devices and suppression systems

3. Normal and emergency means of egress from the equipment and evacuation to a safe location

4. Compartmentalization of the equipment or isolation of areas to prevent or contain the spread of fire

5. Availability of fire-fighting personnel and existing fire suppression equipment

6. Spread of equipment fire to combustible material in proximity

7. Ventilation control structures to contain or redirect products of combustion to the return

8. Any other devices or procedures necessary to protect life and property

  • As mentioned before the South African standards for fire resistance testing is not in accordance with other international practices. It is our opinion that the industry standards should be brought in line, especially as the ultimate goal is to ensure the safety of all working in these environments
  • Even if a fire does grow in intensity or spread to other areas, as long as it burns, toxic smoke and fire gases are produced that can endanger persons within the mine.
  • The belt itself provides sufficient combustible loading to spread a fire without other combustible influences. Major fires have spread on belts and systems carrying non-combustible materials such as limestone and iron ore. Although the conveyed product and the structure may be noncombustible, loss history demonstrates that the belt itself present a sufficient combustible loading to spread the fire without other fuel contribution
  • Conveyor belts liberate dense, black smoke when ignited. This feature can severely hamper manual fire fighting in underground or totally enclosed systems where entry and means of heat venting are limited.
  • Because conveyor belts have relatively slow burning characteristics, sprinklers are very effective in gaining early control before air flow becomes a major contributor. However, where sprinklers are lacking, air flow velocity may substantially influence fire spread.
  • Belt conveyors, whether made of natural or synthetic rubber or plastics, generally are assumed to be capable of self-sustained fire propagation regardless of the presence of other combustibles. For this reason, automatic sprinkler protection has normally been for most installations regardless of the conveyor material’s presumed or claimed fire retardancy.
  • USBM and NCB regulations only apply to underground coal mines. There are not corresponding regulations on the combustibility of conveyor belts in other mining occupancies or aboveground industries.

 

In closing, fires on conveyors should preferably be controlled by maintenance and fire suppression systems rather than using fire retardant conveyor belts. The foregoing recommendations should be considered as a whole and implemented accordingly.

 

Acknowledgements

The author wishes to acknowledge and thank all for contributions in aspects used in this document:

 

Conveyor fires in Canadian hard rock mines: Experience with protective devices at Inco Limited

J. Stachulak, Inco Limited, Copper Cliff, Ontario, and M Scoble, McGill University, Montreal, Quebec

 

Conveyors code of federal regulations

[Title 30, Volume 1, Parts 1 to 199] (Revised as of July 1, 1997)

From the U.S. Government Printing Office via GPO Access [CITE: 30CFR57, 4263]

 

“An investigation of conveyor belt flammability test methods”

WorkCover NSW at Londonderry Occupations Safety Centre (LOSC)

 

Property Loss prevention data sheets 7-11

Factory Mutual Belt Conveyors

 

FPASA bulletin SF10

Fire hazards of belt conveyors

 

NFPA 122

Standard for fire prevention and control in underground metal and non-metal mines

 
Source: Risk Management Solutions
 
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Diversification:

Pooling assets with different inherent risk factors reduces diversifiable risk. Diversification refers not only to the pooling of different kings of assets (shares and bonds), but also to different assets of the same king, e. g. having ten different shares in the portfolio. Due to the small amount an investor has available for investment, he would not be able to invest in assets which require larger amounts unless he pools his investment and shares ...
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