A few years ago, a highly accomplished climber died after she fell out of her harness at a climbing gym. She was using an autobelay, which means there wasn’t a belay partner to go through the customary safety checks with her. She had absentmindedly failed to check her own harness to ensure it was properly secured. She had secured her harness thousands of times, so how could she make a mistake?
Now consider an electrician with 20 years of experience performing voltage checks in a panel. He inadvertently connects his digital multimeter (DMM) as an ammeter across two phases of a 480V circuit. How could this happen? He’s used several different DMMs over the years, and has made thousands of measurements. How can this one result in blowing up the meter in his hand and ending his career as an electrician?
It’s the same principle that is behind the climber’s mistake — and another principle fixes the first. It’s called the safety check. You should have a formal, methodical safety check that consists of a discreet set of steps that is done the same way each time and in the same order each time.
Let’s use that DMM example to show how this principle can be applied. Let’s say this electrician has only one DMM instead of having DMMs for specific purposes. This means that, instead of having a DMM with a red stripe on it that is always used for Class I environments and is used for the 2A current measurements, he has just this one.
His safety script might be:
- Remove test leads and inspect for damage. Replace, if damaged.
- Insert black lead into the black common port on the meter.
- Locate the port for making voltage measurements. Insert the lead.
- Locate the port for making current measurements. Ensure the lead is not in that port.
- Before turning meter on, find the AC voltage dial area or button(s). Set meter up for AC voltage operation.
- Find the amperage dial area or button(s). Ensure they are not engaged. Do the same for the diode function (if present), ohms function, and any other function on the meter.
- Turn meter on.
- Test meter on 120V circuit.
All of this would be done prior to taking 480V measurements. Perhaps it seems silly to check the port for current measurements when you know for a fact you just inserted your lead into the correct port. But that is precisely the point. You may “know” it’s the correct port because you have done this thousands of times, but not because you have verified it’s not an incorrect port.
If that climber had checked her harness prior to hooking in, she would still be alive today. Because something we have done thousands of times is something we can do without thinking, it is dangerous simply because we do it without thinking. Forcing yourself to take specific steps to ensure your setup is safe is a proven way to overcome the absentmindedness that comes with years of repeating a task.
