Failure Modes

Last spring I was doing some work to my gutters and downspouts.  I was running a new downspout extension out past the front of my porch to make it easier to maintain.  So I bought a piece of downspout material at my local hardware store and I was running it along the wall of my front porch.

One of my neighbors was walking by at the time and stopped to see what I was doing.  And he asked me why I was installing the downspout in that orientation.

First let’s back up a little bit and look at how a metal downspout is made.  You start with a long flat piece of metal, as wide as you’ll want the circumference of the downspout to be.

Then you fold up one side.

Then you fold it again.

Then you fold the other side.

And then you fold it again. Now you have a nice rectangular tube, with a seam running along its length.

So you’ll seal up that seam. Maybe you’ll crimp it, or weld it, or use rivets. But you’ll seal it up.

Now you’re ready to sell this to some homeowner, like me, to install.  And how should I install this?  Well, the seam is kind of ugly if you look really closely at it, and so you might be tempted to say that I should install this with the seam facing the house in order to hide it.  And in fact that’s what my neighbor was suggesting.

But I was installing it with the seam facing out, for all the world to see.  And here’s why:  If this downspout fails for any reason, where’s it most likely to fail?  At the seam – that’s the weak spot.  And if it does fail it’s likely to spew water out, maybe at a high velocity if there’s a heavy rain.  And I don’t want water being sprayed against my house like that.  I want water spraying away from my house.

This is the idea of a failure mode.  It’s a matter of understanding how something might fail and designing it or installing it to minimize any damage if it does fail.  Failure mode analysis can be used when designing or installing any object, and it can be used when designing a process.  How is the process most likely to break down and fail, and how can we design the process so that if there’s a failure it will cause the least damage?

If you want to learn more about this idea you can search online for “fail safe mode” or “failure mode and effects analysis.”

I’ve seen several cases of downspouts leaking from their seams and allowing water to spray against the house and cause damage.  Somebody tried to hide the seam rather than use good failure mode analysis and face the weak spot away from the house.  So when you’re installing or even maintaining something in your home, spend a couple of minutes and think about how it might fail, and think about what you can do to minimize the consequences in case of failure.