My kids, from a very young age up to present time, love to ask me a certain question every time I ask them to do something… Can you guess what it is? “Why”, they ask. Every one of us, I believe, are born this way with the natural curiosity of “why” when we are told to do something. So why do we do a main drain test? It always makes a mess; it’s loud and sometimes it even stinks. It’s pretty simple and NFPA 25 spells it out for us in chapter 13. “A main drain test shall be conducted annually for each water supply lead-in to a building water-based fire protection system to determine whether there has been a change in the condition of the water supply.”
Yep, it’s loud, it stinks and it can make a mess, but we must do it every year. Don’t short cut this test and pencil whip some BS numbers in for the static and residual pressures. You’re not doing anyone any good by doing so. In fact, you are putting yourself and your company in harms way when you do. Don’t forget about the “BIG L” (liability) that we all face every day!
When we do the main drain test year after year or quarterly, if its downstream of a backflow or a pressure-reducing device, we have data that shows us if there has been a degradation of the water supply. And guess what? The numbers don’t lie!
For example: A good friend of mine did an inspection at a medical manufacturers warehouse for several years. Every year he meticulously did the main drain test on all of their risers. The water supply was from the city and there was no fire pump. There was a significant decline in the pressures from the first inspection up until the last time he did an inspection. So, what did he do? He notated it in his report and tagged the risers appropriately. The reason he wrote it up can also be found in NFPA 25, chapter 13… “When there is a 10 percent reduction in full flow pressure (residual) when compared to the original acceptance test or previously performed tests, the cause of the reduction shall be identified and corrected if necessary.”
What was the customers reaction to the write up? They fired us their contractor. Yeah, that stinks, but it’s not the end of the world. You see, he did his job correctly. If doing your job correctly gets you fired from a customer, it should make you ask, “do I even want them as a customer in the first place?”
So, what happened? Why did their pressure go down over the years? When the facility was originally built there was not much around it. As years went by the surrounding area kept growing with new construction. The water supply didn’t change. Everyone around them kept tapping into that nice water supply they had all to themselves and their pressure kept getting less and less. THE NUMBERS DON’T LIE. (and neither should you)
Ready for the silver lining? Several years later we found out that the inspection contractor that came in behind my friend wrote the customer up for the same thing. Why? Because they saw his tags with all of the data on them! We found this out because several years later we received a work order to go troubleshoot their fire pump… Wait, what? They didn’t have a fire pump when we did the inspection… They do now! Haha!
How do I perform main drain tests if there is a fire pump?
Great question! I was taught to take my static and residual pressures at the riser with the fire pump running. Yeah, makes sense Eddie, duh… But I bet you didn’t know this excerpt from the NFPA 25 handbook referencing main drain tests with an attached fire pump:
A. Record the static pressure (no flow) reading on the pressure gauge on the suction side of the fire pump.
B. Open the main drain valve slowly until it has reached the fully open position initiating the fire pump operation. Allow the pressure to stabilize, then record the residual pressure reading on the pressure gauge on the suction side of the fire pump.
Don’t feel bad, I didn’t know it either!
What if there are 5 risers on one manifold? NFPA 25 addresses that as well! “Where the lead-in to a building supplies a header or manifold serving multiple systems, a single main drain test shall be permitted.”
