Fool Resistant Design in Fire Sprinklers

Today we have a funny story and a bit of a humorous take on why concealed sprinklers are better than exposed sprinklers. Let’s first cover a bit of background on these sprinklers and where the big problems come in.


Anatomy of a Fire Sprinkler

Sprinklers are designed to be nearly fool proof and as close to failure proof as possible. This means they have to be simple and physics have to be the main source of actuation. To start with, you’ll have all the sprinkler piping, which is pressurized, often by gravity pulling water downwards from higher floors and by the pumps keeping the system full and ready to go.  There’s enough force on the water to dump 100+ gallons per minute for several minutes after a sprinkler goes off without needing any additional pressure from the pump.

The sprinkler head itself is a work of genius. The pipe comes up to it, and it’s blocked off by one of two things: a bi-metal plate or a vial of typically red fluid. These are things we can design to break in response to heat. When they break, water blasts out, hits a spreader, and is blasted out over several feet around the sprinkler head. This is almost as fool proof as something can ever be.

Fire means heat and heat rises. There’s almost no scenario where there can be a fire that the sprinklerhead won’t break. You can choose sprinkler heads designed to near any temperature, so if a room’s ceiling peaks at 150 degrees in the summer without any ventillation or air conditioning, you won’t get a false activation by choosing a 160 degree head. At the same time, it doesn’t take a lot for a fire to make that 160 degrees, so you might lose the contents of that room, but the building will survive.

Anything that trips the sprinklers will also trip the fire alarm and evacuate the building. On older buildings this was done with a fire-bell. The bell had a paddle or a wheel inside the sprinkler piping. Sprinkler activates, water blasts through, turns the paddle, and causes a hammer to beat on a bell until the water flow is stopped. In modern systems we use a flow sensor wired to a battery-backed panel and alarm system.

It takes some seriously freak events for any of this hardware to not work. There needs to be either deliberate sabotage, extremely rare defects, or someone doing something incredibly stupid.



If you’re a fire fighter or emergency responder, I think that title will say it all. On college campuses across the world, there are exposed sprinkler systems  in campus and dorm buildings. In most cases, it was quickest and easiest for the school’s to just put the pipes in and leave them as they were. The same goes for some businesses and land lords: just put the stuff in, set it, and forget it. This is perfectly acceptable in many places and there’s not a thing wrong with it.

The problem comes in when the building occupants overestimate the strength of the hardware or don’t quite understand what that red thing in the sprinkler is. Many students in dorms will use the sprinkler pipe as a convenient rod to hang clothes on. Some especially bold students will stick the hangar directly in the sprinkler head.

Remember we said about that red vial or that piece of metal being the only thing holding back all the sprinkler water? Imagine what happens when a student in a hurry grabs a shirt on a hanger that’s inside the sprinkler head at just the wrong ankle. SNAP. SPLASH. Gargling noises. At full blast, one of these sprinklers will output so much water that the room is drowned in a 6″-12″ pool of water, even with the door standing wide open. It’s not fresh water either. For that first few thousand gallons, it’s nothing but stagnant water that’s been sitting in the system for potentially years. Don’t drink that.

There are others who have thought the red thing was indestructible and therefore, something fun to shoot at with nerf guns and other mostly harmless little toys. The problem is, that red glass vial needs to rupture with barely more than some steam inside it when things get hot. It’s ludicrously fragile. These need a non-existent failure rate, so the glass strength is precise. Have a beer, get dared to hit the target, line up, shoot, snap, crack, sputter and splash.

Lastly, there are people who have looked at the sprinkler piping and thought it made a great chin up bar. This is a great idea, except the sprinkler pipes are nowhere near that strong. If you look up at them, you’ll see hanging rods coming down to support them every few feet. If they were made of titanium, they might not need those supports, but any other metal does. Jump up, grab, count the reps, and somewhere around 100 or so the pipe’s gonna bend, crack open, and you can practice swimming up the stairwell.

This is all extremely expensive. The water will destroy the contents of the room. The facility owner is going to be paying the fire department for coming out, paying their maintenance staff to repair the broken sprinkler, and paying for a fire-watch on the building while the alarm system is non-functional.


Avoiding the Problem

There are two ways to avoid this hassle altogether: educate the building’s occupants or conceal the entire fire safety system. The education route is probably not going to work, because someone is always going to do something silly. The concealed sprinklers however, are a near perfect solution. You cannot hang something on them. You cannot break them by shooting at them. They are a perfect solution to this bigger than you think problem. I was at a department store over the weekend and there was a sprinkler head, within reach of a five year old to just see what happens if he pokes it.

Remember, your fire safety systems are fool proof in that they will work more than 99.9999999% of the time. They are however, barely fool-resistant when it comes to someone with a clothes hanger or a curious finger.

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