I've been doing a lot of research on scenario-based training and the benefits it offers to students.
One of the key building blocks to a good scenario-based course is understanding the assumptions that one makes...
This post will review 3 real life scenarios and focus on the assumptions made by the electricians who were affected.
Assumption 1. It's turned off
This incident happened at a mine site in northern Ontario, Canada.
There was an electric winch that was acting up and two electricians were assigned to determine the cause.
One of the electricians suggested he would go and turn off the switch while the other would wait near the equipment.
On the way to the equipment, the electrician was distracted and took longer than usual to open the disconnect.
The electrician who was waiting figured the equipment must be shut off by now and started to work.
During the troubleshooting process, the electrician came in contact with the live conductors and received a non-fatal shock to his hand and forearm.
What went wrong?
Now you may have been able to pick out a few mistakes that were made along the way but the one I'm highlighting here is the assumption that the equipment was de-energized.
This happens far too often and needs to be taken very seriously.
Remember to always test before touch!
Assumption 2. Shocks don't matter
Have you ever had a shock?
If so, did you do anything about it? Or did you just carry on with what you were doing?
This example takes place at a new installation of a transformer yard.
The transformer was being installed underneath an existing 345kV line and the idea of induced voltages and currents didn't seem to cross anyone's mind.
An electrician was shocked 3 times before finally, the last one was fatal.
But why did it take 3 shocks? Wouldn't the first one be a sign that something is wrong?
This leads us to the second assumption
That shocks are no big deal...
obviously, the electrician did not feel he was in danger and that tells me he was working with bad information.
If someone had told him that 50 milliamps can be fatal, he may have thought twice before continuing on after the first shock.
Assumption 3. 415 Volts is not as dangerous as high voltage
This might be the most dangerous assumption of them all and it's due to the concept of anchoring.
Because some electricians are working with 11kV, 1000V, and 415V systems all on the same day the equipment that is rated 415V seems far less dangerous.
But this is false!
It would be as if a skydiver (who usually jumps at 13,000 feet) were to assume that jumping from a roof of a 12-story building with no parachute is safe.
I don't have a specific scenario, but I ask you to review your own work practices (or the work practices of your electricians) and see if you are doing any of these things... testing 415V with no gloves on, testing 415V without an Arc Flash face shield, operating 415V disconnects without any PPE... I could go on.
Everyone needs to understand that some of the highest arc flash levels are found on 415V equipment and that most shocks at this voltage are near-fatal or worse.