Underground employees at Vale's T-1 and T-3 mines were off work for several days due to smoke.
Seventy Vale employees were evacuated early in the morning on Sept. 20, and normal work didn't resume until the night shift Sept. 23 while crews worked to contain, isolate, and eliminate the smoke.
"The source of smoke was from a bulk production block that had been blasted three weeks ago," explained Stu Waring, Vale's general manager of mines and mills. "It was open unsupported ground, which means it was unsafe for people to enter. Due to the smoke, atmospheric conditions were not at safe levels and required the use of face masks. With the collaboration of mine rescue, the mines branch, USW Local 6166, maintenance and operations, we developed a plan to isolate and eliminate the source of smoke."
"We keep referring to it as a source of smoke because we were never able to see flames," Waring continued. "Judging from the colour of the smoke and the other factors, we strongly believe that it was an old timber structure within old mine workings that was smoldering and not an outright fire."
Once the smoke was detected, a gas known as stench was released into the compressed air and ventilation system of the two mines as per Vale procedures. The stench quickly spread through the mines, alerting all employees as the release of the gas is the signal for employees to immediately seal themselves in designated safe areas and report by phone to contacts on the surface - a process which allowed Vale to verify that all employees were safe and accounted for.
At this point, mine rescue teams were called in, ensured that the escape routes were safe, and brought the employees to the surface. The reason for evacuating both mines is that they are connected underground on several levels. After the employees were all safe on the surface, attention turned to the issue of the smoke itself.
Stench gas is made up of two substances - the first, formally known as ethyl mercaptan or ethanethiol, is a colourless organic liquid, which gives off a strong odour. The ethyl mercaptan is then added to an odourless gas, allowing the combined substance to quickly permeate throughout the area in which it is released. It is frequently used in mines, as it was in this case, as an effective and reliable method of alerting workers to a problem.
To combat the smoke, two small holes - each approximately 4.5 inches in diameter - were drilled approximately 175 feet above the smoky area. Water was pumped through one hole to douse the heat, while the other was filled with sand fill, which would smolder the smoke - and any potential fire - by choking off any oxygen that could serve as a fuel source.
"Although we do not experience many incidents, we still continually practice and test our emergency systems in the event one does take place," said Waring. "The professionalism demonstrated over these past five days speaks volumes to the commitment of our employees and the quality of our training programs. This was a complex situation that was managed without incident."
"When you are working thousands of feet underground and you can't see your target, you have to do a lot of planning and double-checking your plans to ensure the best possible outcome," said Waring. "We developed an initial course of action, adjusted as new information became available, and executed to plan without incident."
