Well, certainly redundancy has a big part of the criticality. And there’s a couple of different ways you can do it, depending on how complex or how simply you want it to be.
The simplest way would be to have the probability of failure reading times the consequence of failure reading equals your risk. And include redundancy in your consequence of failure reading, cut that reading if there’s redundancy.
So if there’s three pumps and you only need two, your consequence of failure is a lower number.
That’s the simpler way because you still maintain just two numbers of probably a failure reading, say from a 1-5 or 1-10 numbering system, you have a consequence of failure 1-5, 1-10 and you reduce the numbers.
Instead of being, say a “4”, is now a “3” or a “2” because you have redundancy. That’s the simple way.
A little more sophisticated way is to keep a separate reading for your probability of failure and your consequence and then add the redundancy factor.
The redundancy factor is 1 if there’s no redundancy, so the risk stays the same. And it’s less than one if it’s got some redundancy.
And you have to decide within your utility what number do you going to use if there’s fifty percent redundant or what number do you want to use if we have 75 percent redundancy or 30 percent redundancy or a hundred percent redundancy.
Keeping in mind that redundancy does not ever take risk to zero. Very important concept that no matter if you have redundancy or not, the risk is always going to be there; that you could lose all of those infrastructure assets.
Say, you have a power failure and all your pumps are hooked in to the same power source, and the power goes out, even though there’s three pumps, there’s three pumps not working. So you have some risks that all are going to fail. We never want that number to be zero.
It’s a number from, say, 0.1 or 0.2 up to 1, and within the utility you decide what numbers we want to give different levels of redundancy.
So you take your probability of failure times your consequence and then multiply it by that redundancy factor to come out with the risk score. The more redundant, the lower the risk would go.
Really I could say that many times the only way to reduce your criticality, is to have some redundancy. There’s certain assets that are just going to be risky.
So if you have, say one well supplying your whole town. There’s a risk associated with that, a pretty high consequence.
If that well fails, the town is without water. So the way to reduce the risk of that asset would be to put in a redundant well so that if something happens to one well, you have another well that you can use.
Many times, we have to have redundant assets. Or in piping networks where often very looped, which means that we have very redundant piping networks. If the water can’t be fed one way because of a break or some problems, you can feed it another way.
There’s quite a better redundancy built-in to most water networks. Most of the time, there’s other ways to flow the water.
PHOTO CREDIT: Josh Hohensee via Flickr Creative Commons License