Underground Mine fires are the industries greatest hazard with disastrous toll on miner’s live and great losses of property and income for the mine.  Most people think of coal mines fires, hardrock mines also burn, the most tragic were 1917 Granite Mountain mine in Butte Montana when 168 miners were killed and the 1972 Sunshine mine fire at Kellogg Idaho with loss of 91 miners.  Despite the numerous fires underground in Bisbee only three men were killed though several were injured.

Types of underground mine fires

• Sulfide

• Electrical

• Timber

• Equipment

The most serious type of fire in Bisbee is when the sulfide minerals, pyrite and chalcopyrite are ignited either through spontaneous combustion or by another type of fire. The oxidation of pyrite and chalcopyrite is exothermic (heat generating) and is sufficient enough to cause spontaneous combustion of the minerals if the heat is allowed to build up. Friction from moving ground (cave in’s) is also known to have generated enough heat to ignite the rock.    The burning properties of pyrite have been known for centuries, even the word pyrite comes from the Greek word pyros meaning fire. Pyrite has been used as an early fire starter and the ignition source on matchlock rifles.    Pyrite and chalcopyrite burn so well because of their high sulfur content, pyrite is 53.3 percent sulfur, chalcopyrite is 34.9 percent.   Pyritic ore dust ignites between 320C and 365C degrees and can burn in atmospheres with only 13 percent oxygen.  In a recent mine accident (not in Bisbee), a front end loader hit the rib of a tunnel igniting the nearby pyrite dust. A high portion of coal mine fires are actually caused by pyrite inside the coal oxidizing and igniting.  Sulfide fires will burn for years, glowing like embers, in 1994 the area around the Briggs fire was still hot.

Chemical reaction of burning pyrite

3 FeS2 + 802=Fe304 + 6S02↑

(black magnetite)

and/or

4 FeS2 + 1102=2Fe203 + 8S02↑

(reddish hematite)

Electrical fires are usually caused by overloaded wires, worn insulation or faulty electrical devices. Hazards from this type of fire are fumes, electrocution and setting the timber on fire. None of Bisbee’s major mine fires were recorded caused by electricity, doubtless there were smaller fires caused by this.

Several timber fires occurred, Bisbee’s poor ground conditions required vast amounts of heavy timbering thought out the mines. The 1907 Shattuck fire started when the timber on the 800 level station caught fire. This fire was put out by spraying water down the shaft and sealing the connection to Cuprite shaft with a bulkhead.  In the Late 1940’s and 1950’s the Copper Queen incline was intentionally set on fire. The Copper Queen incline was ignited by kids dropping a burning yucca down the shaft, which landed near the Queen tunnel level burning the shaft timber from that point to the surface. The Sunrise shaft timber was ignited by a wide-spread brush fire burning the shaft timber out completely.  The Shattuck Shaft and all of the surface facilities were distroyed by this same brush fire, belived to have been accidently set by children.

These vandalism fire were especially dangerous because of how Bisbee’s mine interconnect, the gases could have easily gone from and abandoned section to and active section of another mine. An unusual fire was thought to have been caused by the dumping of molten slag from the smelter near a raise off the 100 drift in the Holbrook No1 mine igniting the timber.

Equipment fires were not as prominent in the past as they are today with diesel equipment being used, the fuel, oil and grease from these easily catch fire. In the past the fires were usually caused by overheated bearings.   This type of fire was not the source of any major fire in Bisbee.

   The fire that caused the horrific deaths of two men was odd in nature.  The incident happen while sinking the Congdon shaft, three men were working at the bottom and were preparing to load a round with powder (dynamite).  The powder ignited and burned fiercely, not exploding. The cause of this fire is unknown. The fire burned all three men severely burned, one man’s skull in split open from a fall which was the cause of death. The other two were recovered alive from the shaft, one later died from his burns.  

Common causes of mine fires     

• Faulty electrical

• Leaving candle snuffs burning

• Careless use of matches

• Spontaneous combustion of sulfides

• Friction of moving ground (cave ins) igniting sulfides

• Careless use of carbide lamps and candles

• Sparks from welding and torches

• Faulty equipment

Mine Fire procedures

 To evacuate the mine, in the early years, they used to flash the electric lights nine times and then repeated, both underground and on the surface to warn the men of danger. Later a Stench system was added which replaced the flashing light or was used in conjunction with the stench.  The stench was the chemical, Ethyl Mercaptan which gives off a strong rotten egg smell. The stench was released in the main compressed air line carrying the smell throughout the mine . Ethyl Mercaptan can be detected at ½ parts per billion this causes problems when training. After the stench was released in the compress airline it would take weeks to get rid of the smell so mines ended up just releasing the stench in the main ventilation during test hoping it would reach everywhere ,which is not very effective. Today mines are switching to a wintergreen stench that is less offensive and they can perform test in the correct manner. After the warning is received the miners will leave the mine by designated routes.

After the mine has been evacuated the next task is to determine where in the mine the fire is burning and then development a general plan of containing and putting it out.  Helmet crews will then be sent in to find out the extent, seriousness of the fire and rescue any trapped miners. At this time the helmet crew will bulkhead of sections of the mine to control the ventilation to the fire country and  keep the escaping gases  from entering into the rest of the mine. In conjunction with the bulkheading , the mine ventilation system will be changed  with fans to create positive air pressure ( 7lb per square ft)  in the fire zone to keep gases from entering through cracks in the rock and around the bulkheads.

Putting the fire out will be difficult and is found to be sometimes, impossible.  There are several basic methods used in Bisbee to fight fires.

1. Flooding the mine to above the fire zone, this was done for the Shattuck fire taking about three months for the water to rise above the fire.  Problems with is that the flooding may require several years. If flooded with acid water which is typical of the water in Bisbee all the steel will be destroyed this will include pumps and pump lines used in the dewatering operations ( before stainless steel was available ).   These problems can cause this technique to be   cost prohibitive.

2. Drill holes from the surface to fire zone and pump water in.  Difficulties with this were they have had trouble drilling holes above the fires because of the broken and caving ground.  A benefit can be derived from this technique in sulfide fires, the water running through the fire zone will act as a leach solution dissolving  the copper. Collecting the “copper water” below the fire zone, from which the copper can be recovered from the solution by making a precipitation plant underground.

3. Driving drifts above the fire and flooding them and letting the water seep into the fire zone. You can also drill hole from the drift and pump water into fire

4. Use fans to build up air pressure and force smoke and gases back towards point of the fire’s origin and mine the fire  out

5. Bulkhead off fire zone letting it burn and keep surrounding area cool with ventilation to keep fire from spreading.

6. Shaft fires where sprinklers have been placed inside shaft. The sprinklers can only be turned on if the fire doors on all the shaft station are shut or all personal are out of the mine. The turning on the sprinklers will cause a change in ventilation pattern and can forces the fire gases into other parts of the mine

7.  Shaft fires in  wood timbered shafts without sprinklers should have steel shaft doors installed at the collar and these will be shut after all the miners have evacuated .