Sprinkler System Failed: Why Firefighters Couldn't Stop the Warehouse Fire

Added: 2026-05-11

[00:00:00]a 1.2 million square foot warehouse in California burnt to the ground even though it seemed to have a functioning suppression system. Let's look at a suppression system and find out why.

[00:00:13]Let's see that again.

[00:00:22]Before we get into what went wrong in the warehouse, you need to understand what a sprinkler system actually is.

[00:00:27]Because most people have no idea. This is Stashed. I'm Pat, mechanical engineer and firefighter.

[00:00:34]A sprinkler system is a designed system.

[00:00:36]It's engineered for a specific building, a specific occupancy, and a specific fire load. That means the engineers look at what's inside the building, how fast it's going to burn, and design a system that can handle it. The last part matters. It's designed to handle a specific scenario, not every scenario.

[00:00:54]Buildings get repurposed all the time. A building that started as a light storage facility becomes a high piled warehouse packed floor to ceiling with combustible goods. The occupancy changes, the fuel load changes, but oftent times the sprinkler doesn't. Now, in the case of the Ontario, California warehouse, to be fair, that system was probably designed correctly for what was inside. It was a high bay warehouse, paper products, plastics, consumer goods, packed floor ceiling. That's a high fuel load, and the engineers would have accounted for that. But here's what they can't design for an arsonist. This wasn't a fire that started in one place and spread. The guy walked through the building and lit multiple fires. Spread across a massive area at the same time. The moment that happened, the suppression system was fighting a completely different battle.

[00:01:43]And it's not something it was designed for. Sprinkler heads are activating all over the building simultaneously. And when too many heads open at once, pressure drops, flow drops, and the system becomes ineffective almost immediately to show you exactly how that works. Let's see a demonstration. This is a simple wet pipe sprinkler system.

[00:02:02]One riser, and let me walk you through it pretty quickly. Water comes in from the city water supply here. First thing, it hits a control valve. This is how you shut the system down for maintenance or an emergency. For example, somebody bust a sprinkler head by mistake. Then it goes through a backflow pre. Quick side note on that. The water sitting inside these systems, it gets nasty. When we drain a system like this, the water comes out black. When you bust a sprinkler head by mistake or in a fire, that water looks disgusting. The backflow pre is there to make sure water can't flow backwards into the municipal water supply if pressure drops. It's an important piece of equipment. From there, we move to another control valve and into a riser. The riser is the main vertical pipe that feeds water to all of the sprinkler heads. Now, there's also a second way to get water into the system, the fire department connection. We can pump directly into the system from outside. You'll notice there's a check valve here that makes sure water can't flow out of the building through this connection. But that's it. A very simple system. If you're not subscribed, now's a good time. I'm trying to hit 100,000 subscribers this year. Now, in a building like the California warehouse, the system would look a lot more complex. Multiple risers, multiple zones, and almost certainly a fire pump to boost pressure during an event. More infrastructure, more capacity. But here's the thing, it doesn't matter how robust the system is. Break enough heads simultaneously and you lose pressure every single time. Before I go and break more sprinkler heads, let's look at the gauge. We can see we have extraordinary pressure in our city. For us, it's pretty standard to see 90 to 100 PSI at our hydrants. In this case, we have a static pressure of 90 PSI. That's a healthy system ready to go. So, let's set off two sprinkler heads and see what happens.

[00:03:56]You can see and hear the pressure behind them. And if you look at the gauge, you'll notice we dropped down to around 75 PSI. We're still at a reasonable pressure to make this thing work. Now, I would love to go around and bust a bunch of sprinkler heads to show what happens.

[00:04:12]Unfortunately, I couldn't get a building rep to go along with the plan, so we had to get creative. We have a stand pipe and a four-story training tower connected to this system. So, we connected a 2 and 1/2-in hose on each floor. Four floors, four hoses, with each one of those hoses flowing wide open to simulate multiple sprinkler heads going off at once. Now, I want to be clear here. This is just rough math.

[00:04:34]a 2 and 12 in hose and a bunch of sprinkler heads. They flow very differently, but this is in the ballpark of right around 20 sprinkler heads activating at once. Again, we're going to start with two sprinkler heads flowing, dropping from 90 to 75 PSI.

[00:04:54]And now we're going to open up the valves and flow a bunch of water.

[00:05:10]We went from 90 PSI all the way down to 0 PSI as we maxed out that flow rate.

[00:05:15]You can see the sprinkler head is flowing very little water right now.

[00:05:18]It's essentially useless. Now, you might be wondering why we still have water flowing even though we're at 0 PSI.

[00:05:24]That's because this system's a little unique because it's a demonstrator and it's not meant to demonstrate this exact thing. These sprinkler heads are actually the lowest point in the system.

[00:05:34]And those sprinkler heads are essentially acting as a drain for the system. In a real system with the sprinkler heads in the ceiling, I would expect that flow to nearly stop. Here's a sidebyside comparison.

[00:05:46]You can see a big difference in the flow. And that's likely what happened in Ontario, California. 175 firefighters showed up to a building where the suppression system had already lost the battle. Not because it was broken. It failed because it was asked to do something it was never designed to do.