SAFETY CODE ONE

We were chattering about Safety Code Six a couple of columns ago … and while it’s still fairly new and it’s of interest to Industry Canada in particular, today I want to talk about something eminently more down-to-earth. No one has ever been demonstrably harmed by electromagnetic radiation at a broadcast site. Contact currents can burn us, and we’ll likely remember it for quite a while, since healing from this is notoriously slow. But you won’t die. The greatest hazard to life that we face in broadcast engineering is electrocution. We deal with high voltages and currents routinely, and very safely—there are not a lot of casualties in our business. But there are a few, and they rightly tend to make news. Perhaps they’ll act as a deterrent to future accidents…

OHM’S LAW APPLIED TO A SHORT CIRCUIT

You are alone at a transmitter site that has a surge suppression system installed at the main distribution gutter, i.e. after the main hydro disconnect, but unable to be de-energized on its own breaker or cutoff switch. There are six status lights on the front of the suppressor box, and two of them are extinguished, indicating that an internal fuse on one of the three phases has blown. You know that you should not replace a fuse while the circuit is hot, and you know that you should not work on this by yourself. But no one else is around right now, and to kill this circuit would take the station off the air, so you really should come back late at night, and you’d rather not have to do that, so you figure you’ll just be extra careful, and you’ll ensure that you don’t become part of the circuit.

But what you don’t realize is that the fuse blew in the first place because the MOV’s inside the suppressor module have failed destructively by shorting, and when the fuse is replaced, the replacement fuse instantly explodes in your face, causing second and third degree burns there and on your arms. As you stumble, dazed, out of the transmitter building into the open air, the door slams shut behind you, locking you outside with your keys inside. But you are lucky to be alive.

An air conditioning technician was killed in Vancouver earlier this year, when he powered up an HVAC unit that was accidentally wired to short. He was not electrocuted. The short caused the switch panel to explode when he powered up. Part of the panel blew off and struck his head. He was not wearing a hard hat.

OHM’S LAW APPLIED TO THE HUMAN BODY

You are alone at the transmitter site. You are having a pesky problem with the power supply intermittently overloading. In order to get a better look, you defeat the interlocks and leave the back door wide open while the transmitter is operating. After a while, you get braver, and start carefully poking around inside the cabinet.

You wake up lying on the transmitter building floor. You have no idea how you got there, or how long you’ve been unconscious. The transmitter is still happily running, with the back door open. Eventually, much later, you notice small burns on your back and one of your feet. You, too, are lucky to be alive.

OHM’S LAW APPLIED TO THE HUMAN BODY, PART II

You are a chief engineer at a transmitter site with your assistant, and you have a nasty transmitter problem. You eventually are able to solve it, but many hours have passed, and you are very weary. Now you’re just cleaning up the transmitter to place it back in service, and have finished dealing with the high voltage circuits, so you feel pretty safe. Unfortunately for you, you’ve become tired and careless, and although you don’t contact the high voltage, you do come in contact with 120 VAC. In your weakened condition, your heart stops. Your assistant is able to summon help and apply artificial respiration until help arrives, but you never completely recover your faculties, and never are able to work again.

These accidents all happened more or less the way I have described them. And they all happened to experienced technicians, not newcomers to our trade. Let’s continue this theme next month.