If any of you have tried to use a 5x5 risk matrix to determine the risk of an arc flash or electric shock hazard, then you will know what I am talking about. It just doesn’t work!
Likelihood or probability on the vertical and consequence or severity on the horizontal.
To use the matrix properly you would have to look at a specific task you are doing, determine the likelihood of an incident happening while performing that task and then determine the consequences if the incident did happen. Multiply the values you gave for each and come up with a risk score.
For example, falling off of a ladder while painting the trim on your front porch. Each step you take up the ladder you are increasing the consequences of the fall but the likelihood of falling probably stays about the same (because all the steps are the same). So at each step, the score on the matrix is getting higher and higher.
Once you determine the score for that particular task you can use that information to decide whether or not you want to take any additional safety precautions… maybe fall arrest in this case.
So why doesn’t this work for electrical hazards?
The main reason is that when you are working with electrical hazards it’s as if you are working on the very top rung of your ladder, and you are not painting the trim of your front porch anymore, you are painting the trim of the roof on a three storey building!
Yes. Here’s why.
If you get a shock that passes through your heart it only takes about 50 mA (that’s less current than it takes to light a 60-watt light bulb in your house) to cause ventricular fibrillation, or in English to cause your heart to stop working properly, which of course can be fatal.
If you are exposed to an arc flash of only 1.2cal/cm2 (and trust me most are calculated to be much higher) then you are going to have 2nd-degree burns on your entire body… barely survivable.
Now you are starting to see the issue with the risk matrix. Every time you do anything with electricity, if something goes wrong, the consequences or severity is extremely high. Giving you a score of “25” or whatever number you use in your matrix as the highest possible risk.
You can use the matrix if you want but it’s a lot of extra work for nothing. All you really need to do is use a binary risk system… 1 or 0. Yes or No.
How do I use a binary risk system?
I think I just made this term up but I’ll roll with it… if all electrical incidents are high consequence then what variable can we look at to determine if we have a 1 or a 0? The answer is “abnormal condition”. Am I interacting with this electrical equipment in a way that can be considered abnormal? That’s what you have to ask yourself every time you are working on or near electricity. If the answer is ‘yes’ then the risk = 1 and you need to take extra steps to ensure your safety.
I’ll try using examples to show you what an abnormal condition is.
Reading a panel meter… risk = 0
Operating a disconnect switch… risk = 0 (for the most part… email me or look me up on twitter if you want to go deeper on this one).
Using an infrared camera… risk = 0
Insulated cable inspections… risk = 0
Testing a live electrical circuit…. risk = 1
Operating a disconnect switch that has not been maintained in 30 years… risk = 1 (this is what I’m talking about in the example above).
Removal of bolted covers… risk = 1
Starting to get it?
So scrap the risk matrix and go binary, it’s way easier and you will get better results. If you end up with a 1, then dress appropriately and take any extra precautions you may need.