Late in the startup of a plant I was tidying up the loose ends, and early that day the maint guys asked that I clear the line if product from last night in an area so they could do some PMs/training of the new guys. Sure thing, no problem. We've run the line dozens of times so far full and empty of product. about a half hour before they were to do their training I started firing up the line to empty it out, leaving the infeed off so as to not load more in. It takes a little bit for the line to start up, motors have to spin up, you can hear them quite well. After 30 seconds or so I realize it doesn't sound right. It spins up to a pretty loud high pitch.. it didn't reach there. Stayed lower with the wrong harmonic. SO I look over. I don't see my piece of equipment I expect to see. Its about 28ft long, 8ft high, 5 ft deep and RED... What I do see is a cloud of smoke about 40ft long, 20ft high... and probably gotta be 15ft deep.
F***! Slap the Estop to kill everything, then throw all fixed run switches to stop (just in case someone pulls the estop back up) . About a minute later guys with fire gear, supervisors, etc come pouring in from outside, we check and verify there is no fire so we can relax a bit. Lockout time and start investigation. Fortunately we only burned some belts. While we're talking it pops into my head.. I saw a mech walk over to the air supply lockout and put his ganglock and lock on it. But there was no sound... Normally when you let the air loose from this system there is about 5 seconds worth of a seriously loud venting. So while the mechs, supervisors check over the equipment itself further for possibly more hidden damage (none was found), I found the source of the problem.. Remember I said the air was locked out? The tags for the Air pressure switches... were reading as True. So I track them back to... nothing. They were mapped no where. Nothing wrote to them to inform them of the status of the inputs. Continued to dig and found what those actual Inputs were mapped to... a slightly different name. Instead of being Zone2, they were mapped to Zone3. Not uncommon as its based on what motor drives the chain.
This should have been caught before we ever ran product. No one ever tested whether it would fire up WITHOUT AIR. The permissive are to prevent startup without air. Problem is when your reading a BOOL that you can toggle and nothing is writing it to a certain state... your permissives are no use. Corrected it, found other places the wrong tags were used and corrected them. Made some screen caps of before/after of each wrong tag location for my incident report.
Why did the belts get burned? Well with the air off, the blades drop down into cut position, however by chance someone had previously stopped the line with the blades embedded in wood. the blades could not turn with the lumber holding them. Which is why air is a requirement for power up of that motor. Air on is blades up, logic forces all blades up during startup.