I am a firefighter in a town of around 1200. The other day we had a house fire and used a hydrant (which up until recently was a rarity in this town). Anyway, later that same day a main was found to be leaking SEVERAL blocks from where the fire was. Through the grapevine, we heard that our city administrator blamed this on the fire department. So my question is, how often do mains break as a result of firefighting operations?
If you were pumping the hydrant, you could collapse a line in the system at any weak point. Water hammer is something that could be a cause for concern but I don't believe (my opinion) that the water hammer can go anywhere past the pump and into the water system with any affect. In the year 2009, I find it extremely sad that there are no back-flow prevention devices on hydrants. This could eliminate this issue (if in fact it was caused by water hammer) and also would prevent any contamination of water systems.
If the driver/operator is doing a proper job and watching his panel,
there will be an almost NO possibility of breaking a main through a
miscalculation. He should ALWAYS leave a positive intake pressure
on his guage (20psi MINIMUM) and be attentive that he doesn't "run
away from his water". Also, if the relief valve is properly set at the
panel, then any water hammer resulting from sudden shutdown of a
line will be diverted from the supply system. Again, training is the
most important thing here.
Another little trick is whenever possible,the D/O can leave the "tank
fill" valve open and the "tank to pump", thus recirculating water and
lessening any concussions from a water hammer.
If the firefighters on the line are properly trained, they will know that
it is safer, easier and more controllable to open and shut the nozzle
in a smooth action and not abruptly. This not only prevents a water
hammer, butlessens any reaction form stopping./startin streams and
also prevents the possiblility of rupturing a line as well as a main.
I'm in a volly dept. in which the area covered, and it's surrounding communities involved in mutual aid, does not have hydrants. So, therefore, we don't train in it. I want to move on to a career FF position and will need to know some of this information. Thanks.
So by "sucking dry"...do you mean that the pumper is trying to get more water than the hydrant can produce?
I wouldn't do this, but I have seen it done a couple of times. Garage fires that were very quickly knocked down by 'laying a line' and attaching a nozzle to the supply line. This was when we used 2.5"/3" for supply lines so you can tell it was a long time ago.
I am the head of our Water Dept and it can happen on even well maintained systems. We have had mains burst from supply line valves shut down to fast (water hammer) Quarter turn valves are the easiest to do this with as we have had a water operator do this also. Condition of the pipe and soil conditions also contribute to this. I preach to the guys open slowly and close slowly! As far as backflow on hydrants Mueller has just came out with a hydrant with a flapper valve in the bottom boot. Retro fitting old hydrants is cost prohibitive.