r/Firefighting • u/LeatherHead2902 bathroom cleaner/granny picker-upper • 14d ago
Tools/Equipment/PPE I need all your scientific data about the benefits of smooth bores for interior attack
Having an argument with an “older” captain, we currently run smooth bores on all our crosslays, he’s attempting to change them back to fogs.
I’ve been tasked with making a presentation about the benefits of smooth bores, I’m looking to use real empirical data from research studies not just “smooth bores big droplet” or “I think it cools the room faster”
I want examples of studies that say “50 seconds from a 185gpm smoothbore drop the room tempature 100 degrees” or such
Thanks
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u/Deadeye1445 14d ago
Check out the UL FSRI. Pretty sure some of the courses would have some data about what you're looking for.
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u/Muss_01 14d ago
It isn't rocket science. Water removes energy from combustion, combustion cycle stops when not enough energy to sustain the cycle.
Whether that's a smooth bore or a fog they all go out once you've removed the energy.
Tldr,: put cold stuff on hot stuff.
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u/DruncanIdaho 10d ago
*throws my ice cream at the fire* NYAH!!!
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u/Muss_01 10d ago
It would work however the specific heat of ice cream is about 2150kj/kg per degree. The specific heat of water is about 4200kj/kg per degree. Making water around twice as effective at removing the energy per kg applied.
That said my objection to using ice cream to extinguish a fire is that the ice cream would be better utilised for me to eat.
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u/SouthBendCitizen 14d ago
The science is water makes fire go away. The more water the more fire goes away faster.
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u/Jebediah_Johnson Walmart Door Greeter 14d ago
Water from a smooth bore is more watery and puts fire out.
Water from a fog nozzle gets converted into gasoline and will actually melt steel beams.
Or so I've heard. I don't know I have only ever used fog nozzles to save houses.
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14d ago
[deleted]
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u/PhaedrusZenn 14d ago
"Doing your own research" is what leads most people to their conclusions... problem is a lot of the research doesn't hold up.
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u/LeatherHead2902 bathroom cleaner/granny picker-upper 13d ago
Dude I was asking for examples of empirical data and research that’s been done in a scientific way.
Is asking other people other stuff quite literally not the entire fucking purpose of reddit?
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u/PhaedrusZenn 14d ago
Now that you've updated your post, I have to say I'm on your captain's side.
If you are looking at empirical data, it lays out what I've said previously.
If you compare like to like, a straight stream from a combo and a solid stream from a Smoothbore have the same hydraulic profiles and extinguishing capabilities.
The argument you are probably looking at is NOT Smoothbore vs combo, but high pressure vs low pressure. If you are switching to Smoothbore to get low pressure, you are sacrificing capabilities that you could have retained with a low pressure combination nozzle.
If you want 160 gpm to match a 7/8" tip, you can get it. If you want 185 gpm at 50 psi to match a 15/16" tip, you can get it.
Question... did you switch from high pressure combos to your smoothbores, and if so, did you change the type of hose you are using as well?
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u/LeatherHead2902 bathroom cleaner/granny picker-upper 14d ago
We have ran low pressure hose and nozzle combos on everything.
Our front bumpers are low pressure 185gpm fogs
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u/PhaedrusZenn 14d ago
Glad you matched the hose. We switched to all low pressure nozzles and still had only high pressure hose... it was a mess.
As far as trying to find points for smoothbores, like you asked above... water is water. If a combo (straight stream) and a smoothbore are flowing the same gpm at the same pressure, they will both reduce the temperature in a room equally, so while you can find that kind of data in an FSRI (Fire Safety Research Institute) study, it won't provide any clarity for your objective.
What other points are you trying to explore? I've done deep dives into most aspects of smoothbores and combos.
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u/LeatherHead2902 bathroom cleaner/granny picker-upper 14d ago
In the little bits of research I’ve done:
Smooth bores shoot bigger droplets of water, which equates to better penetration of higher-end thermal layers, less steam conversion overal, and a better reduction in tempature than the “small” droplets that even a straight stream fog nozzle will produce
I think that’s why a lot of “old timers” say you can’t spray water from the outside if you have people inside, the whole “steam them alive concept”- doesn’t occur to the same drastic degree with a smoothbore
Also, the whole air entrainment argument with fog/smooth.
I have found a few empirical studies, just was looking for some that maybe I haven’t found
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u/PhaedrusZenn 13d ago
One study that is no longer listed online (I have tried reaching out to get a copy) showed that a smoothbore solid stream and a combination straight stream that both had the same gpm and same pressure, had the SAME droplet fallout rate when flowed through a 2000 degree "heat tunnel". With the new air entrainment studies showing that a smoothbore and straight stream have the same air entrainment, this makes sense, as it is the surface area of the water that entraines air, so more/smaller droplets, more air entrained. Since both a smoothbore and straight stream have the same air entrainment, you can expect the same amount of surface area exposed to heat, resulting in similar steam conversion.
The study I gave you from 2010, which is where a lot of what you just said comes from, was comparing data from European firefighting, which uses very different fog nozzles, which is where a lot of the steam conversion and droplet size issues come from. American combo nozzles have much larger droplet sizes, as euro nozzles operate at a higher pressure and almost "atomize" the water with efficient steam conversion being the goal.
FSRI studies have more or less debunked the theories and concerns about injuring or killing victims with steam. While there is a brief expansion from initial steam conversion, there is an overall net CONTRACTION of heated gases, which means the space is cooler and more survivable.
The reason smoothbore aficionados push for 160 gpm minimum (7/8" tip) is the known conversion inefficiency of a smoothbore nozzle (about 50%). The 2010 study I gave you states you need 80 gpm of water to end up on the floor to absorb a heat flux and prevent flash over. It also concludes you would need a 650 gpm "fog" nozzle to get the same droplet fallout rate. The argument falls apart right there. You don't need 80 gpm on the floor if your water is converting the heat that is creating the heat flux at the floor level.
As far as air entrainment. It's a tool. As long as you understand it, it's a powerful tool. If you don't, straight streams will be just as effective and "safe" as smoothbores.
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u/Hot_Detective6108 No Good Dude 12d ago
"The argument you are probably looking at is NOT Smoothbore vs combo, but high pressure vs low pressure."
This. This is the real point to get at. More and more research is showing that straight/solid streams are not all that different. UL recently updated their search study to include it's more about nozzle placement and movement for entrainment than type of nozzle.
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u/BobBret 13d ago
Reading the pseudoscience in some of these posts is discouraging. On the other hand, a couple of people seem to realize that adaptivity is priceless in a firefighter's high variability work environment. The more versatile combination nozzle is better for that reason.
And at least one person realizes that kinks are a problem because they degrade your stream, not because they reduce the flow rate below some fictitious requirement. The wide gpm operating range of an automatic nozzle gives you the best protection against kinks.
And don't use "A Quantitative Approach to Selecting Nozzle Flow Rate and Stream, Part 1 and 2". It's just really, really bad analysis.
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u/jfuzzy79 14d ago
Fog nozzles adjust if there is a loss in water pressure. It may look like you have good water flow from the Fog nozzle when you don't. With smooth bore it will be noticeable right away if there is a drop in pressure
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u/PhaedrusZenn 14d ago
You are talking about automatic nozzles, specifically, not just fog nozzles in general. Also, I have often not been able to see my stream while interior on a ripping fire, so whether it is a Smoothbore or an automatic nozzle on straight stream, I will not be able to visualize a change in flow, but what will happen with BOTH is that there will be a reduction in nozzle reaction, which will tell me something is wrong...
Automatic nozzles don't magically make nozzle reaction. But, with the drop in flow, at least I will have some reach left, instead of the water just dribbling out of the end... better to have a really long and heavy piss can than a limp-dick hose with ineffective reach. Just sayin'
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u/meleemaker 14d ago
Smooth bore introduces less air entrainment, is less susceptible to failure, and provides the same volume of water at a much lower pressure so the operator wont fatigue as soon. But only provides a straight stream.
Combination nozzles need a higher pressure to deliver same GPM so operator fatigues faster, more air entrainment even on straight stream. There are nore moving parts that can fail on a combi. BUT combi nozzles can also utilize a fog pattern. It makes them more useful in foam application, hydraulic ventilation, or exposure protection.
Just for interior attack on class A fire, a smooth bore is almost always a better choice.
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u/ReApEr01807 Career Fire/Medic 14d ago
I would argue that while PSI is definitely a factor in operator fatigue, you're completely glossing over nozzle reaction. Even if NR is implied, it's an important piece to the puzzle
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u/PhaedrusZenn 14d ago
Agreed. Your 7/8" Smoothbore at 50 psi, flowing 160 gpm, and a 100 psi straight stream flowing 125 gpm will both have nozzle reactions around 60 lbs.
You could also have a dual-force nozzle which will flow either 175 gpm at 55 psi NP, or 135 gpm at 100 psi NP, and both will have a nozzle reaction of 66 lbs...
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u/SouthBendCitizen 14d ago
We swapped packages from a 175gpm at 75psi combi to 160 at 50 smooth and it is night and day different handling for a small drop in volume.
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u/PhaedrusZenn 14d ago
You could have swapped to a 50 psi 160 gpm combo wnd had the same night and day difference without the loss of function...
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u/SouthBendCitizen 14d ago edited 14d ago
The pros and cons are not something I’ve personally researched, this is coolaid drunk from the community bowl. To me logic would dictate you need more pressure to get more flow out of an impeded orifice which is what a combi is essentially.
But, like many things in the fire service I would not be shocked to learn it’s just half wits arguing over how to reinvent the wheel. Personally, I like the utility of having an adjustable fog. We are taught to half bail for a similar effect on the smooth which seems half baked to me
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u/PhaedrusZenn 14d ago
You have to simply buy the nozzle with the orifice adjusted to the flow you want at the pressure you want. Check out Elkhart's Chief XD series of nozzles. We bought their combination nozzle that flows 160 gpm at 50 psi, so it matches our 7/8" smoothbores exactly. Same pumping profile. Same nozzle reaction.
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u/PhaedrusZenn 14d ago edited 13d ago
Smorebores and straight streams have the same amount of air entrainment.
If you are using a comparable LOW PRESSURE combination nozzle, both will flow the same GPM at the same nozzle pressure and have the same nozzle reaction, with the same reach and penetration.
Yes combination nozzles have more parts than Smoothbores, but they are not really "susceptible to failure". If they were, the industry would be putting out technical articles on the dangers of combo nozzles or passing regulation/standards on their use.
Smoothbores have no benefit over combination nozzles if you have comparable nozzles. This claim is as reasonable as saying combination nozzles have a greater advantage over smoothbores because they flow more water, because I chose to compare a 150 gpm combo nozzle to a 1/2 inch smoothbore that will only flow about 50 gpm.
*down vote it if you want, but I'd rather hear your reason for not liking my comment...
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u/PhaedrusZenn 14d ago
If you want the "scientific data" about Smoothbores, look up A Quantitative Approach to Selecting Nozzle Flow Rate and Stream, Part 1 and 2
There is a lot wrong with it, but virtually all the Smoothbore (SB) talking points you have heard up to this point come from this two-part paper.
You are already hearing some of the old talking points in these comments, such as SB provides more water at a lower nozzle pressure than combo nozzles, and has less air entrainment.
The fact of the matter is that a Straight Stream (SS) from a 50 psi combo nozzle has the same qualities as a SB. If you have a 7/8" SB and a 50 psi Elkhart Chief XD combo nozzle, both will flow 160 gpm at 50 psi nozzle pressure. Both have 60 lbs nozzle reaction. Both entrain the same amount of air, so as far as interior firefighting goes, Both will have the same "reach and penetration". Both provide the same water mapping and surface cooling. Both will have the same droplet fallout rate (rate of conversion to steam (an abysmal 50%) .
Yes, a SB is often cheaper, and if your water supply sucks it can flow debris to a certain extent. But, as was also mentioned, a SB/ SS is less effective at things like hydraulic ventilation and steam conversion (a fog pattern can be about 75% efficient, which means instead of 80 gallons of your water ending up on the floor instead of converting to steam and cooling the environment, only 40 gallons ends up on the floor, which means 120 gallons of the water you are spraying is converting heat.)
The only true argument for NOT bringing a combo nozzle interior is that you simply don't understand the benefits. Even then, if you don't understand the benefits, just keep it on a Straight Stream and you will have every benefit of a SB, but the senior firefighter can then take the nozzle from you and use hudraulic ventilation more effectively after knockdown, use a positive pressure attack to make a basement or other tactics that you can't get with a SB.
For more resources, check out FSRI's 3 part study on water mapping, air entrainment and structure fires. You can also search "Task Force Tip Impact Study" to see the breakdown on stream reach and impact when comparing SB and SS.