Northfield: Fans and Fools
When you have a construction project with multiple drill and blasts tunnels being excavated through a single portal and access tunnel, things can get crosswise in a heartbeat. The tunnels are ventilated by a system of forty eight and fifty four inch lightweight steel fanlines. The air for ventilation is moved through the fanlines by huge inline axial fans powered by high speed electric motors. The fans are reversible and can blow air into the tunnels or pull air out of the tunnels. The axial fans are often bolted end to end in tandem to increase volume and efficiency. Adequate ventilation is required to remove diesel exhaust fumes, powder smoke, and other air contamination. Operations have to stop when no ventilation is available.
We used Koehring Mine Dump trucks at Northfield. They had a double set of controls in the cab. When the dumpy was going forward the teamster faced forward and drove like a conventional truck. When the dumpy went backwards the teamster rotated his seat to the rear and used the reverse facing steering wheel and controls. You would think driving a dumpy in a tunnel would be pretty straight up and simple. Not so. We were on graveyard one night with several crews working in different areas. The tunnel power flickered and all the ventilation systems shut down. We soon received word to cease all work. A dumpy returning to the portal after emptying his load of muck never lowered his dump bed. He hit the portal with the bed up at normal speed and wiped out all the ventilation facilities including the fans mounted in the roof of the 24 foot tunnel. I would have loved to have seen the expression on his face when he hit that portal.
When shooting a normal twelve foot production round in the tunnels we would turn off the fans during the blast. Once in a while somebody would screw up. When the explosives detonated in a delay sequence they created a series concussions and vacuums within the tunnels. If the ventilation system was pulling air out of the tunnels the vacuums would cause the fanline to collapse. Often we would have to remove and replace twenty or thirty pieces of fanline because no one shut the system down.
The ventilation system gets more sophisticated as work progresses further into the mountain with more tunnels and excavations completed. More fans are added underground to compensate for the distance and areas requiring ventilation. The fans have to be shut down and started in a rigid sequence to prevent system damage. It never fails. Somebody would start a fan in the wrong direction, create a vacuum, and collapse a bunch of fanline. The only thing you can do is cease production until things are repaired. The repairs could take several shifts.
Our project supervision didn’t appreciate the shut downs…………………….but the local bars appreciated the extra business when miners couldn’t work