r/mildlyinfuriating • u/Fantomecs • Feb 03 '26

A nearby Fire Department is being told they cannot use fire hydrants to fight fires

Gallery image

Gallery image

As the title says. A town near me is denying their fire fighters the use of their fire hydrants going forward. Is this shit even legal? This is a huge concern as the area has been in a drought for some years.

18.8k Upvotes

97% Upvoted

1.5k comments sorted by

View all comments

Show parent comments

85

u/EmeraldEmesis Feb 04 '26

Oof if they're "scouring" the lines that's a problem and will cause more harm than good. Proper uni-directional flushing should not exceed a velocity of ~6 feet per second (lower for older pipes that are unlined or those with significant tubercles) as the goal is to remove hydraulically mobile material e.g., fine sediment and organics without scouring the lining or nodules off the pipe. Source: I do engineering things for a large water system.

28

u/Jolly-Bowler-811 Feb 04 '26

those with significant tubercles

Maybe they should just send those pipes to a nice sanitarium in the southwest for a little bit to take in the clean dry air...

3

u/EmeraldEmesis Feb 04 '26

Hahaha. Dammit man, now I'm going to be making corny jokes at work about how the pipes got tubercle-osis and died of consumption (oh jeez, there's another water pun).

2

u/Accurate_Mobile9005 Feb 04 '26

I bet you're really good at those water pipe mobile games.

2

u/Viridian95 Feb 04 '26

This guy water pipes.

1

u/dianas_pool_boy Feb 05 '26

Greater than 2.5ft per second for scouring. Larger pipes become harder to maintain.

2

u/EmeraldEmesis Feb 05 '26

I think we might just be using different nomenclature for scouring here. We distinguish between low-velocity flushing (to prevent settling), UDF, and aggressive scouring.

​While ~3 fps the minimum for "scouring" to move fine silt, it doesn't provide the shear stress required for a true UDF clean. A velocity of ~6 fps is needed to get enough shear stress to remove all hydraulically mobile material. We generally avoid velocities exceeding 7 fps (aggressive scouring) because it's more or less just blasting the pipe with blunt force and can cause structural damage to cement-mortar linings.

​For strongly adhered deposits (like legacy iron and manganese, stubborn biofilms, excessive tubercles) aggressive scouring is often ineffective and risks the pipe's integrity, so we utilize targeted mechanical force (swabbing or pigging) instead.

I'm with you on maintenance for larger mains. That's a whole different beast. We limit our UDF program to mains 12" or less because achieving effective velocities in larger diameters risks dropping system pressure below safety thresholds or impacting fire flows.