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The Parallel Intake Mine Ventilation System

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Major Disaster Case Studies

 

Braden Copper Co.'s Copper Mine - Chilean Andes - June 1945

Though details remained hazy, investigators conjectured that a maintenance man who had been told to grease some ore cars on the day shift decided to warm a can of grease that had congealed in the cool mountain air by placing it near blacksmith's forge just off a main intake airway.

The unattended grease soon ignited, eventually touching off a blaze that soon spread to nearby timbers and to a repair shop where kerosene, paint and grease were stored.

At 0740 hrs, a chief mechanic spotted the blaze and telephoned officials on the surface. Twenty minutes later, while the evacuation was still underway, an explosion ripped through the repair shop, blowing out bulkheads and fire doors partially damaging an underground winze hoist. The ventilation in this main escape shaft, normally upcast, suddenly reversed, motivating clouds of smoke and heavy concentrations of toxic gases down into lower levels, effectively blocking the shaft as an escape route.

Soon the underground hoist rooms of two other winze shafts filled with smoke and were abandoned. Of the 1,000 miners who worked that morning, 630 escaped, another 25 who had barricaded themselves and survived on air from compressed air lines were later rescued, with 355 miners dead of carbon monoxide poisoning.

Major underground mine fire disasters within the past 13 years have dramatically illustrated how a variety of fire protection shortcomings can have tragic results.


Cargill Inc.'s Belle Isle Salt Mine - gulf coast of Louisiana - 1968

Here, miners wrongly believed that the single, wood-lined shaft was relatively fire resistant thanks to the fine salt particulated which had impregnated the timber surfaces.

Late on the night shift of March 5, the hoistman received a telephone call from the surface maintenance man who was performing routine maintenance on the skip at the 1,100 level shaft station underground. "Come on down with the north side, the shaft is on fire!"

Shortly after the skip arrived, a miner called out "the skip is on fire, we can't get on it," he yelled. Paul Granger, the underground foreman, cut in. "Go to the radio, get some help.....get a lot of help," he was reported to have said. A voice broke in and kept repeating, "Pour some water down the shaft..."

The relief hoistman shouted to run water down the shaft. When he approached the water line just a few feet from the shaft, he discovered the water hose missing.

The crew of an oil company boat who had landed at the island shortly after spotting the smoke was sent to shore and returned in a few minutes with a hose. Unfortunately, when the hose was finally attached to the water line and the valve was turned on, nothing happened.

Somehow the pump had lost its prime. When company officials arrived an hour later, the pump was fixed and water began to trickle down the 16-foot diameter, 1,250-foot deep shaft - two hours after the fire had first been reported.

Fire equipment that had arrived in the night from the mainland continued to pour water into the shaft until the fire was quenched.

For the 21 men trapped underground, it was too late. The coroner's report issued weeks later fixed the time of death for 20 of the men at 0600 hrs, about six and one-half hours after the last phone call from underground.

The other man had died of a skull fracture shortly after the fire started, the coroner said.

His quick death was probably a merciful one. Though equipment abandoned around the shaft station indicated that the miners had desperately fought the fire for a while, rescuers discovered their bodies huddled in two groups far back in the mine where they had slowly succumbed to the terrifying effects of a gradual carbon monoxide poisoning.

The specific cause of the fire was never determined, but, investigators deduced from the evidence that the fire had started somewhere below the 1,100-foot level shaft station and then had rapidly spread like smoke up a chimney, quickly burning through the plywood partition that divided the shaft into two compartments.

The absence of adequate fire protection and fire fighting facilities at and in the shaft coupled with the lack of a second escape route had doomed the miners from the beginning, investigators concluded.

A standard requiring two main escapeways to the surface, or a refuge station in lieu of the second escapeway in the mines under development, was promulgated in February 1970. It was a standard that could well have saved the miners at Belle Isle.


Sunshine Mining Company - Northern Idaho - 1972

The massive Sunshine underground silver mine had two escape shafts. The primary man-hoisting Jewel shaft was the mine's main intake air shaft and it serviced both the 3,100-foot and 3,700-foot levels of the operation.

The Silver Summit shaft, once the main shaft of an adjacent silver mine, now served as an exhaust airway, located about two and one-half miles from the Jewel and about one and one-half miles from the underground No. 10 shaft.

The No. 10 shaft winze began on the 3,100-foot level and serviced all workings on down to the 5,800-foot level, a development area.

Though no raises connected 5,400, the 5,600-foot levels to workings above, several raises did serve as secondary escapeways, for miners working in the 4,800-foot level up.

In any case, it was a long climb up even in fresh air, and the No. 10 shaft offered the only quick access to the 3,100-foot level and to the Jewel shaft.

For the 173 miners who went underground on the morning of May 2, 1972, the shift began like any other. An hour before, two night-shift repairmen smelled what they thought was smoke as they rode on a mantrip toward the Jewel shaft station.

Seeing no smoke, they concluded an electrical motor or somebody smoking a cigarette. Not until around 1145 hrs did miners in several locations of the 3,700-foot level begin to smell and then see smoke curling into their work areas.

When it came, it came fast.

Two foremen near the No. 10 shaft station on the 3,700-foot level decided to investigate and followed the smoke to the 910 raise several hundred feet away where smoke was coming down the normally upcast raise from the 3,400-foot level.

When they returned twenty minutes later to the No. 10 shaft station, one of them telephoned the surface and gave instructions to activate the mine's stench alarm system.

Meanwhile, smoke had rapidly filled lower levels. For many miners working there, there would be no escape.

The No. 10 shaft was equipped with two separate man hoists. At the 3,700-foot level, a 9-person single drum "chippie hoist" serviced all levels below.

Shortly before 1155 hrs, the "chippie" hoistman was driven from the hoistroom by smoke. That left a double drum counterbalanced skip hoist on the 3,100-foot level the only other chance for escape.

Hung below the two skips were small cages capable of hauling nine people each. The shaft foreman who earlier had given orders to evacuate consulted with the hoistmen and the two agreed that using both skips would slow down the evacuation because of the extra braking and clutching required. Only one skip remained to lift miners from the workings below.

Over the next half hour, several miners reached their respective level shaft stations and were hoisted to safety.

Still others decided to go back into working areas to alert miners while waiting for the cage to return. Many had broken into the underground caches of the filter-type self rescuers, but for most, operation of the devices was a mystery.

Miners who finally determined how to use the self-rescuers passed them back and forth to others who had none. As men began to drop from exhaustion and the effects of carbon monoxide, many still on foot made futile efforts to drag their partners to safety.

Unable to continue in the smoke, the No. 10 shaft hoistman turned over his duties to the relief hoistman, at 1235 hrs one of the several cage tenders who had volunteered to remain underground to help with the rescue entered the hoistroom minutes later. Finding the relief hoistman shaking with weakness, he gave the hoistman a self-rescuer and told him how to use it.

Sometime after 1300 hrs, the last time the cage came up to the 3,100-foot level, the hoistman was overcome by carbon monoxide and later died.

The last means of escape for those below was now blocked. The cage tender was the last man to escape from the mine that day.

Earlier, a miner escaping from the 3,700-foot level through the Jewel shaft thoughtfully removed lagging which had covered a borehole in hopes that fresh air form nearby shaft would by drawn to miners at the other end of the borehole on the 4,800-foot level.

Seven days later, Ron Flory and David Wilkinson were rescued from that location. Of the 173 men who had gone underground that day, 80 escaped, two were rescued, and 91 had died of carbon monoxide poisoning.

Among the dead were several who had initially escaped but had returned to participate in the rescue effort. Still others had deliberately remained underground to aid their fellow workers.

The magnificent displays of courage tragically demonstrated the unwritten code of kinship shared by underground miners, but too often these events also reveal a great lack of knowledge about what to do in a mine emergency.

Bureau of Mines investigators concluded that the fire probably originated in an abandoned area adjacent to an exhaust airway on the 3,400-foot level. These areas had been mined more that 20 years before, were backfilled with waste rock, timbers and other refuse and bulkheaded off from the rest of the workings.

Supplied by air that leaked through into the area, the fire slowly spread and eventually reached the bulkhead where it burned through.

Thanks to the 95,300 cubic feet per (45m3/s) of air that was coursing through the exhaust airway, the fire grew rapidly, releasing great amounts of smoke and gas when then short circuited into nearby raises and eventually into 3,100 and 3,700-foot levels and workings below.

The heavy concentrations of carbon monoxide measured during the rescue efforts and days afterwards were evidence, Bureau officials believed, that the fire had been a fuel rich one that could have smouldered for weeks before its discovery.


Wilberg Underground Coal Mine - Utah - 1984

The failure of mine management to remove a faulty air compressor from service was the primary cause of a fire which caused the death of 27 miners. That was the conclusion of the MSHA investigation team in its final report.

While the report closes a two-and-a-half year investigation into the cause of the accident and its resultant fatalities, the agency continues to investigate possible criminal violations of mine safety standards.

Investigators concluded that the air compressor located on the section where the fatal fire began was not properly installed or maintained.

Ventilation of the air compressor station was not adequate to prevent the recirculation of cooling air to the compressor. The over-temperature safety switch was intentionally by-passed and the on/off switch linkage was disconnected so that the air compressor had to be turned on and off at the 5th Right belt drive power centre. In addition, the air compressor was not frequently examined or tested to identify potentially dangerous conditions.

"The air compressor was inadvertently turned on and operated continuously for about 69 hours before the fore started. The fire quickly spread with the airflow and caused the early failure of the aluminium intake/belt overcast blocking the other designated escapeway", concludes the final report.

The report also lists nine factors which contributed to the severity of the accident. These factors included: an increased number of miners present on the section die to an attempt to set a production record; failure to respond to the first notification of smoke in the intake entry; and inadequate training in the use of self-rescue devices, fire fighting procedures and evacuation.

The fire which began at about 2100 hrs on December 19, 1984 claimed the lives of 8 supervisors and 19 union miners. Initial fire fighting efforts failed to control the fire which hampered rescue attempts. By December 21 the fire had been contained enough for rescue teams to enter the section and account for 25 of the 27 miners. Nine bodies were located only 200 feet beyond the fire.

Rescue teams were withdrawn from the mine as the fire burned out of control. In an effort to extinguish the fire, the mine portals were sealed.

Following numerous varied attempts to reach the fire are, crews were successful, after 11 months, in mining new entries into the 5th Right section where the miners had been working when the fire broke out.

Twenty five bodies were recovered during the first seven days of November, 1985. The locations of the other two bodies were still unknown.

On December 17, 1985, the remaining two bodies were located some distance apart from each other further back in the mine.

With the bodies recovered, MSHA turned its attention to determining the cause of the fire, and in September 1986 issued preliminary findings which indicated that the faulty air compressor was the cause of the fire.

Emergency Response Considerations

Self-Contained Breathing Apparatus

Drager PA93

Hazardous Chemicals

Drager BG174

Drager BG4

Gases

Fire

Fire Fighting

First Aid

Rope Rescue

Case Study - Pasminco Fire

Glossary

Summary of the Principles of Rescue Work

Guidelines for the Frequency of Practice Sessions


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