|(I need to put in a caveat right here and now, that I am NOT complaining about or disrespecting my FD. We are very aggressive and are fortunate in that most of our fires do not require large exterior flows. We take good care of our citizens, and they take good care of us in return. We get there quick and hit it fast and hard, over powering the fire with enough water to stop it in it's tracks. I am merely pointing out that if we (or any FD set up similarly to us) were to make small, subtle tactical changes, such as what I am writing about in this blog, then effeciency in rapid fire attack of large fires would drastically improve.)|
Ok, so on an earlier post, I started a quick spout about how I'm not a huge fan of the 2.5" attack line.
Most FDs out there that I have been on and worked/trained with generally use 1.75" hose, 2.5" hose, and large diameter hose (LDH) in either 4" or 5" sizes. Many, but less, FDs also use 3" hose. Back in the day, there was ONLY 2.5" hose (except the booster line, which is a glorified garden hose, and not part of this blog). Then someone developed 1.5" hose, which was great for attacking smaller fires. However, it's flow is limited to not much more than 125 GPM. For larger fires, the 2.5" line would be used as an attack line, flowing nominally 250 GPM. Much more punch than a 1.5", but a lot heavier, too, requiring more manpower.
"I'm not a huge fan of the 2.5" attack line. If it were me, I'd have all my attack lines using smooth bore tips. My ideal pumper (wait, I thought you said you like truck work over engine work? Yes, I do, but that doesn't mean I don't know anything about engine work) would have a large pump - 2000 GPM - and three 1.75" attack preconnects; with three more 2" attack preconnects; a pre-piped deck gun; a tailboard mounted portable gun with a 500 GPM rating, preconnected to a dead-bed of two- to five hundred feet of 3" hose, and a large capacity hosebed of five inch supply hose. More on that in another blog."
Then in the 70's (?) or 80's (?) 1.75" was developed, and for the most part has replaced the 1.5" hose as a primary attack line. The 1.75" which can nominally flow 185 GPM, is only a little heavier than a 1.5" line, but with significant more knockdown power, thus making it safer for firefighters.
About that time, companies started developing "automatic" fog nozzles, which are spring loaded to maintain a certain nozzle pressure (generally about 100psi). They are good products, and when properly maintained, work well, as designed. So when I say fallacy, it is not directed toward nozzle manufacturers.
The fallacy with automatic fog nozzles is in the belief by members of the fire service (that's firefighters, folks) think that because the stream looks good, therefore they must have a good flow. Flow tests have proven time and again that just because a stream looks good, doesn't mean it is flowing. I've participated in flow tests, and online there is plenty of documentation, to show that a 1.75" line with a stream that looks good can be flowing as little as 100 GPM. So much for being safer - hauling a heavier line with less flow than the old 1.5" lines... Hmmmm....
So what can be done to overcome the low flow? Pump it properly! Some nozzle manufacturers claimed you could get the same flows as a 2.5" hose (250 GPM) out of a 1.75" line, using their nozzle. And you know what? It's true! You can! But...
To attain those kinds of flows, first we have to determine the friction loss so we know where to set the pump. For a 1.75" hose, there is 96 psi of friction loss (FL) for each 100ft of hose. Since most hoses are set up between 150ft and 250ft (average being 200ft), well, that's friction losses anywhere from 144 psi to 240 psi to overcome, with the average 200ft line having 192 psi in friction loss. Then we must add nozzle pressure. For the automatic fog nozzles, it's 100 psi. So now you have to pump the line at anywhere from 244 to 340 psi, with 292 psi for the 200ft line. Can our pumps handle that? Sure!
But, we need to remember, the 1.75" is by nature a very squirrelly line. It is not docile, like the 2.5" is. We also need to remember nozzle reaction. A fog nozzle flowing 250 GPM has a nozzle reaction force of 126 lbs. That is manageable, with a docile line. When you have a squirrelly line, you not only have that force pushing back in a straight line, you also have it swinging the firefighters from side to side, up and down, as well as backwards. So, is the 1.75" a two person line? Not at those flows.
I think it is unsafe, personally, and my guess is a lot of other firemen out there think so too, as the automatic nozzle push seems to have died down over the last several years. They are still available, and like I said above, they are fine products that do what they say they will. The problem isn't the knob, the problem is us.
So why not just go back to the old system of 1.5" attack for small fires and 2.5" attack for large fires? I do believe that it is safer having a larger flow available than the 1.5" can deliver, given the contents of most occupancies these days (plastics are the norm, which are essentially solidified petroleum, and when they burn, they burn fierce and hot).
But Ken, earlier you said you advocate replacing the 2.5" hose altogether. What gives? I'm glad you asked.
I'm in the camp of using 1.75" and 2" attack lines. The 1.75" line efficiently flows 185 GPM, which has a FL of 53psi/100ft, and with a 100 psi fog nozzle it has a reaction force of 93 pounds. Using a 15/16" solid tip with a 50 psi nozzle pressure, the nozzle reaction force is 69 pounds. Quite a difference, ain't it! Same flow, and a lot more manageable to boot! Still squirrelly, but not like the 250 GPM reaction and squirrelliness.
For higher flow requirements, tradition says we pull a 2.5" line and flow 250 GPM. Remember the fallacy of the automatic nozzle. Crews can think they are flowing high flows because they have a stream that looks good, but in fact have a stream that flows not nearly what is needed to absorb the BTUs given off by the fire. Put a 1.125" straight tip on a 2.5" line and operate it with a 50 psi nozzle pressure, and you are flowing 265 GPM, with 99 pounds of nozzle reaction force, and FL of 14psi/100ft. Easier to pump, easier to handle, but VERY heavy to drag around and make an aggressive fire attack with. If a FD has manpower out the whazoo, ok, but let's deal in reality - most paid (read fully staffed) FDs are staffed with three on an apparatus, if that. Some are lucky to have two men on an apparatus. My FD has two companies with four men, and the rest with three. We are blessed. Volunteer FDs (read - not staffed fire stations, where members have to drive to the station to get the apparatus, and they are lucky to have one member on an apparatus. Not slamming, just pointing out reality.)
Instead of using a 2.5" line, I advocate using a 2" line. But it's smaller! Yes, it is. It is also significantly lighter than the 2.5" hose, and CAN flow the same 265 GPM using the same 1.125" solid bore nozzle at 50 psi of nozzle pressure. It has the same reaction of 99 pounds, but only has 56psi/100ft of FL, compared to the 96psi/100ft of FL the 1.75" line has at 250 GPM. The 2" is only a little heavier than the 1.75" line, and yet it is docile, like the 2.5" line.
Hmmm... a line that ain't too much heavier, is easier to control and move around, and has the punch of a 2.5" hose... I dunno about you, but I like the concept quite well!
So, can we use the 2.5" hose to supply a portable monitor? Sure you can, but why would you want to? Remember, you can flow more than 250 GPM through a 2.5" line, but you start putting bigger friction loss numbers up. A portable monitor has 25 psi of FL just in the monitor. Then add nozzle pressure (80 psi for solid tip on a master stream, 100 psi for fog tip). Now add your friction loss. It adds up. For instance, if you are pumping a 2.5" hose at 500GPM, that is 50psi/100ft of FL you have to overcome. If it's a long lay, well, then you start needing relay pumpers and such.
But Ken! We can lay two or three 2.5" lines to the monitor! That should reduce the friction loss, and increase the distance we can pump! You're exactly right. But, again, why would you want to? Pump that same 500 GPM through a 3" hose, and you only have 20psi/100ft of FL to overcome. Using 4" or 5", the FL goes down even more. The problem with 4" and 5" is they are heavy lines to hand jack very far.
On my FD, the pumpers have a 500 GPM portable monitor with a choice of a 1.375" solid tip or a 500 GPM rated fog nozzle. They stay in their compartment. It is unfortunate, IMHO. I'd rather see them pre-mounted to the tailboard, connected to hose. My FD doesn't have 3" hose, but we do have 2.5". The theory is if we do need it, we'll pull a 2.5" preconnect, take the nozzle off, and use the monitor. Our 2.5" preconnects are 200 ft long, and at 500 GPM that means we'll pump 100 psi just to overcome the FL, then 25 psi FL for the monitor, then either 80 or 100 psi for the nozzle pressure. 205-225psi is quite doable. However, not too much more can be added to extend the line, because the FLs will make it counter productive.
If we (or any other FD) were to use 3" hose for the portable monitor, then we could theoretically pump it at much further distances (like 500+ ft away) as we only have 20psi/100ft of FL to pump. Using a single 3" line to a portable monitor, while the hose itself is heavier than the 2.5" line, will in the long run save time and energy, when compared to stretching multiple 2.5" lines.
Okay, that's enough of a rant for now. Please note that I did NOT mention Compressed Air Foam Systems (CAFS). For the record, I AM a fan of it, have used it and seen what it is capable of. My FD has two CAFS pumpers now, and I presume will have more in the future. However, like the booster line, it's not on topic for this blog.
Thanks for reading.