Episode 27 | 3 dB / 6dB rules, design pricipals, and more

This episode explores fire alarm design principles, NFPA 70 Article 760, and key considerations like the 3 dB and 6 dB rules, high air movement effects, and code compliance. Experts Bryan McLane, Charles Aulner, and Chris Godwin share insights on practical applications and exam tips.

Transcript

SPEAKER_01 0:03

Hello again and welcome to the Temporal 3 Podcast. Today we're going to talk all about fire alarm. I am joined by my co-host, Mr. Charles Ulner. Hello, Charles. Hello. Hi. And Mr. Chris Godwin. Hello. Well, guys, I'd like to start out today talking about a topic that certainly is a relatively simple topic, but does cause a lot of confusion with fire alarm people, and that is the 3DB and 6DB rules. Chris, talk to us a little bit about the 3DB and 6DB rules. What are they?

SPEAKER_02 0:38

We use these rules to help establish the spacing of our audible appliances. Now, all Audible is going to use a 6 dB rule for figuring out your distancing, your spacing. It's based off of the inverse square law, which states every time you double the distance away, you lose six, and you just keep doubling until you are within your required sound level. Whether that's public mode or 15 dB above or your private mode, 10 dB above, doubling the spacing until you get 15 or 10 above the ambient sound level. 3 dB rule is for speakers, only speakers. And what the 3 dB rule states is every time you double power to the speaker, you will lose 3, or sorry, you will gain. You gain 3 dB more. 3 dB rule is used to establish the baseline of what the appliance is going to produce. The problem is out in the field, and especially with design, it doesn't get used that often because of combination devices, combination appliances, your horn strobes, your speaker strobes, where the limiting factor is never what is the audible doing. It's always going to be, you know, the visible side of it. So that's a big thing that when you get into like the nice hit exam, people struggle with that for a bit until they finally get on get comfortable with it, and then they get the ball rolling and have an understanding. But it is just one of those things that I've seen from students that you know, they'll tell me, I've been doing design for a while, never had to use this. Most of our designs are going to be combination devices. So it it it doesn't, it doesn't get used that much.

SPEAKER_00 2:20

Charles, what's your take on this? Well, uh, expanding on what Chris said, it's a legacy issue. Back in the day, many, many, many years ago, several decades ago, strobes were expensive. Horns were less expensive. So using a combination device wasn't as common as it is now. Uh so what you would do is you'd figure out how many uh strobes you needed and how many horns you needed, and they were considered separate, really. Nowadays, we just stick a horn strobe up wherever we need to. Uh so the 6 dB and the 3 dB rule is less important in terms of spacing now than it used to be. Um we really had to do the calculation back in the day when they were considered separate. Nowadays, the strobe is always the the factor because uh the horn sounds loud enough with the spacing of the strobes. We don't have to worry about the the decibels so much, Brian.

SPEAKER_01 3:36

You know, I hadn't even considered that. You're absolutely right, because you think about I'm I'm old enough to remember the 1992 ADA law that completely turned fire alarm up on its on its head. And where uh previously we had basically uh white strobes that said fire on them, and all of a sudden this ADA law comes out, and everybody is producing these uh 117 candela strobes that draw like 250 milliamps, and there's all kinds of requirements, and then of course 72 evolved to add those tables and stuff like that. And you're right, way back when, when we just used those uh basic, not very high-intensity strobes, it's basically a flashing light, um, yeah, it was a lot uh a lot easier back then, certainly. But with the uh the visual intensity requirements, the visual requirements being added to the code based on the ADA law, that kind of turned things out in its head. I never really considered it from that perspective. I think you're right about that. So, Chris, you mentioned about uh in the real world in design, uh we, you and I both, and particularly you have experience with a couple of design programs. Have you found any design programs that'll do these 3 dB or 6 dB calculations for you?

SPEAKER_02 4:43

Uh there's nothing that I've found. No, this is something that as a designer, uh you got to know how to do. It's not like the software is gonna do it for you. Now, like we were saying, horn strobes, speaker strobes, they've they've taken this out of the field. They've taken it not maybe not completely out of the field, because you still want to make sure that you are going to be at least 15 above, but for the most part, it's not something that a lot of designers are really using. And it it it's one of those things that really bites them in the back end when it comes to testing, when it comes to, hey, this this isn't producing enough. What do you mean it's not producing? It's they've got over their overlapping coverage all over. How is it not?

SPEAKER_01 5:28

Well, you didn't calculate. Yeah. You have a high ambient noise area, and uh your coverage of the audible gets reduced, then it really becomes an issue, and that's something people don't necessarily consider. Charles, from the NISET perspective, is this something you think people will see on the NISAT exam?

SPEAKER_00 5:44

Likely, yes, especially at level three and four. Uh this is something that NYSET likes to throw in there. It's a calculation. It's something that uh I'm gonna say this, although it's my perception, not necessarily NYSET's reality, that uh they seem to want to make things difficult and confusing on the test. And this is an area that they can really accomplish that. Um one thing I'll say about it too, and I I think it's important, is this is annex A type material. The 3DB rule and the 6 dB rule are for uh design guidance purposes only. If you really want to make sure that your devices are gonna function the way that they're intended, what do we have to do? Get out there and measure it. Yeah, we have to use uh a sound meter. Get out there and follow the requirements of the code, set that thing up for 24 hours, see what the average ambient and maximum sound levels are. Right. Uh base it on what's actually happening on the ground.

SPEAKER_01 7:00

Absolutely. That's it's an interesting take on it, too, because uh you're right. That is really the crux of it. You know, these if you have a high ambient noise level, even though you have design guidance, you talked about it being in Annex A, but it again it is design guidance, just like they provide design guidance for average ambient sound levels in annex A as well, an 18 A1844. Yeah, A1844. But it's only, as you said, Charles, guidance. It is not necessarily reality, and the reality in the field is what makes that determination. It means whether or not the radio the AHJ that comes in there, I used to say Radio Shack. Nobody knows who Radio Shack is anymore. Uh Amazon's special DB meter and says, okay, uh, you know, five feet off the floor, you're not meeting the sound level requirements, fail, you got to add horns. The other thing I was going to say about that too is something that we need to consider is that audible uh notification design is performance-based, not prescriptive. That basically the code doesn't tell us how far apart to put the horns, says you've got to meet this DB level. Probes are prescriptive. We know what the strobe requirements are based on the size of the room and location and intensity of the strobe. What audibles, I hate to say a crapshoot, but they really are a crapshoot. That uh sometimes, you know, if you don't plan ahead, if you don't plan properly, uh you could end up basically having to add more audibles. So yeah, definitely an interesting uh topic. So I'd like to turn next to code. I'd like to talk about a favorite code of ours, NFPA 70, the National Electrical Code, uh, the uh code of the electricians, shall we say, but that does have a bearing on the work we do in fire alarm systems. And Article 760 really is the heart of the matter for fire alarm people. And Article 760 is actually broken into four parts. And I don't think a lot of people realize this when they work in Article 760, and knowing that it's broken into parts can actually help you navigate it, even though it is only about 10 pages. Not a lot to work with, but it is something that's going to be on your NICET exam. We have to have familiarity with it in the real world for those discussions with the AHJ. And the parts are part one for general requirements, part two for non-power limited fire alarm, part three for power limited fire alarm, and part four for listing. But I'd like to focus today on part one, some of the general requirements. So, Chris, what do we find in part one? What are we gonna see in there?

SPEAKER_02 9:29

A lot of repetition from chapter three, honestly. But you are gonna have stuff that is very specific to your fire alarm systems, your fire alarm system wiring. You don't have to have it in conduit, but it does have to be in enclosures if you're gonna be doing any kind of splices. Anything that's gonna be a break in the circuit, in the wire itself, has to be in a box or enclosure. That's something that is specific to 760.

SPEAKER_01 9:53

Chapter one or part one, yeah.

SPEAKER_02 9:56

Yeah, right there at the beginning of part one. It gives you that information. Protection of the circuit. Um, also, one other thing is is lightening. Well, what uh what we like to talk about is lightening the fire load of the building. You got abandoned cable, it's gotta be removed. You've got uh you're going through any kind of fire or smoke barriers, it's gotta be sealed back up. And a lot of that information is right there at the beginning of 760.

SPEAKER_01 10:24

Charles, what's your favorite part of uh 760 part one?

SPEAKER_00 10:29

Do you have a favorite? Uh Chris hit it, and I think this is really important from an understanding the perspective point of view. The abandoned cable issue, it's gotta be removed. But who's responsible for removing it becomes the big question. As a fire alarm technician, if you observe abandoned cable, does that make it your responsibility to take that out? And uh obviously the answer is no. The code says it has to be removed. Does it say it has to be removed for free? No. No, it doesn't. And Brian, who's responsible for removing that cable? Whoever the AHJ says.

SPEAKER_01 11:21

And uh and ultimately it's the building owner, but the AJ. Yeah. Yeah, the building, the uh AHJ can point the finger at whoever he wants. And you know, it's an interesting topic of discussion because we've heard from a lot of fire alarm people. Yeah, I got hung with uh removing abandoned cabling, and most build um a TM requirement into their contracts for abandoned cable, but here's the quandary of the fire alarm people. We are the last trade in there. Uh, we're after the HVAC people and the painters and the plumbers and the electricians, uh, and the building can't open without our system. Fire alarm's not complete, building's not opening. So the AHJ a lot of times will pick on us and say, hey, you're the last trade, you're the guy within my field of vision, you're removing it. And uh it definitely presents a challenge.

SPEAKER_00 12:07

One of uh my there's another part of that too, Brian, that I think is really important. Uh as that wire load increases in a building, sure, there's uh uh fuel for the fire argument, but there's something else that happens too. And uh that is when the drop ceiling falls in a real fire, what's all that cable doing? Yep.

SPEAKER_01 12:36

Yeah, it's coming down on whoever's in the building.

SPEAKER_00 12:39

And it's happened that firefighters get tangled up in that spider web of abandoned cable or cabling, and it's a real hazard for our first responders. So making sure that our cable is properly secured and abandoned cabling is removed becomes uh a safety issue for firefighters.

SPEAKER_01 13:06

So I got to tell you guys what my favorite part of Article 760 Part 1 is, and the one that I hear see so many pictures and so many uh uh hear so many horror stories about, and you guys know where I'm going with this neat and workmanlike manner. My personal favorite is hearing stories or seeing pictures of the fire alarm panel or any panel of the guy opens the uh the cabinet door and a cascade of wire falls at his feet. And uh that one is just a personal pet peeve of mine that um uh thinking about technicians and the amount of time that it takes to deal with and sort through that mess, and uh neat and workmanlike manner is not defined in 70. So that becomes the domain of the AHJ, and it's up to the AHJ to enforce that neat and workmanlike manner of installation of the system. If you guys have uh experience with that, have you guys seen that, particularly from your field experience? Rat's nest?

SPEAKER_02 14:08

I've definitely seen plenty of rat's nest. A lot of times it's above this, above the ceiling, like we were talking about, but I've had plenty of panels where I opened up and I was like, why am I getting smacked in the face? This is not right. What's going on here? Or I've got to pull, I've gotta pull the knacks off, and it's there's no way to get your hand in there without getting bit by the animal that is all of that wire that's just been yep, push it in, push it in. It's fine. Just get it in there and you'll be done with it. No, it's gotta be done in a neat and workmanlike manner. Unfortunately, there's there's not an elaboration on what that means, but it's in the code. It's in the code. But also in the code is that your fire alarm cable has to be read. Yeah, yeah, exactly. 760.30. I mean, the words don't say it. You have to Da Vinci code it. You gotta read it between the lines. 760.30 basically, you know, tells us, and and this is right at the beginning, getting into that, you know, part one. Your fire alarm circuit has to be identified at all junction and terminal locations. Absolutely. The word read somewhere in there. You just gotta Oh, yeah.

SPEAKER_01 15:18

I guess they get like I said, you gotta Da Vinci code it. You've got to call Tom Hanks and a re read diagonally across multiple lines. Yeah. You were saying well, Charles.

SPEAKER_00 15:28

I just want to make sure everybody realizes that Chris is uh full of malarkey when he says that. Because it came across as maybe that's true. It's not true, people.

SPEAKER_02 15:39

That's not true.

SPEAKER_00 15:40

Fireball cable doesn't have to be red.

SPEAKER_02 15:43

Yes, if you're listening. We bring that up in class, and and we I'll read the entire reference and and I'll tell everybody. See, it says right there. Everyone's lost. And then I have my favorite joke of all time where I actually highlight across three different lines in one paragraph. No, it doesn't say anything about it, it has to be red. It doesn't have to be red, it has to be identifiable. It has to be identifiable at all terminal and junction locations. That's all code says about it. But you ask most of your AHJs, and code says it's got to be red.

SPEAKER_01 16:13

That's not that's not accurate. Just in case those of you that are uh listening only and not seeing the expression on Chris's face when he tells his story as Charles uh confirm. No, it does not actually say red. Nope. Nowhere. Well, guys, our question from the field for this uh session is about high air movement. Student asks, what is high air movement and how does it impact smoke detector spacing? Chris, what is high air movement and what does it do to smoke detector spacing?

SPEAKER_02 16:42

If you have high air movement that's greater than 300 minutes per air change or per change, it's gonna have an effect. What a smoke detector is looking for is smoke. Smoke is uh essentially weightless, and if you have air blowing the smoke all over the place, it's not going to be able to get to the detector in the way that we need it to. So when we have areas with high air moment, you gotta adjust the spacing so you have more detection. You have more detection so that when that air pushes your smoke in a different direction, it's going to another detector. It's not going off towards the wall, away from it. It's going to be going and blowing towards another detector. So when we look at that, that's what we're trying to do. It affects the spacing because it's going to push my smoke away.

SPEAKER_01 17:30

So and in NFTA 72 and 17.7, 1777331 particularly talks about eight minutes per change or 7.5 changes per hour, and there's a table that shows the spacing of the detectors. It also notes that that does not apply to underfloor or above ceiling spaces as well. So if you're uh underfloor detectors, above ceiling, or mechanical rooms are exempt from this requirement. Not a common thing. Not uh not don't see a lot of areas um where you have that high air move, but but is that something you may see on the nice it exam, Charles?

SPEAKER_00 18:07

Absolutely. And there are some applications for this. I'll throw out a couple of uh concepts. One is uh garage uh where mechanics work and they have vehicles running in an enclosed space. They set up air movement in those spaces to push out that exhaust air and bring fresh air in. Another one, Chris, you're really familiar with being a Las Vegas native, those casinos or some of them allow smoking. And they have specific air movement in those spaces to push out that smoke and keep it fresh on the casino floor so people aren't offended by that smoking residue, so to speak. And when you have higher air movement in areas like that, hey, we have to reduce our smoke detector spacing in order to compensate. Yeah.

SPEAKER_02 19:09

That table doesn't really tell you exactly information. A table's a frustration because it tells you what your square footage coverage is with the table. First time I saw that, I was like, okay, so I'm using I'm using 125 feet now. What is going on? I don't understand. How do we go from 30 to 125? That's not how that works. You got to figure out the square, what the square root is, and then that's what your spacing is. But coat doesn't like, doesn't really stipulate how to do that. It just says, here's your information. Good luck.

SPEAKER_00 19:42

When the board of directors at NICE that see this podcast and hear about your confusion, they're gonna say, yes, mission accomplished. What we wanted the whole time.

SPEAKER_01 19:56

I'll tell you one that I uh considered, again, it's not real common, but something that's been in the news a lot lately, so I may think it makes a great example is data centers. And it's not the subfloor, it's not the below floor uh detection or the above ceiling detection, it's in the data center themselves and servers. And if you have detection in the servers, uh you know, if you're using spot type or if you're using uh air sampling type, and air sampling type usually is space the same as spot type, you know, 30 feet. You have a high amount of air movement in a data center and you have smoke detection in the servers, you're gonna have to put those holes closer together or put those detectors closer together based upon the amount of air movement. It does come into play. It's not a common thing, it's definitely a higher level thing, uh particularly in the NISET exam, but something to be aware of nonetheless. And as Chris said, the way the table's written, very, very confusing uh and requires you to think a little bit and do a little bit of math. But does NISET love confusing stuff, guys?

SPEAKER_02 20:52

Yeah. Yes, absolutely.

SPEAKER_01 20:54

Absolutely. Absolutely. Well, gentlemen, I appreciate the conversation today. As always, interesting and informative. I want to thank all of our listeners for joining us in the podcast. Please remember to subscribe and guys, have a great rest of your day. You too, Brian. Have a good one, Brian.