Steps to Layout Fire Sprinklers?
NOTES & SUMMARY
CODE & STANDARD REFERENCES
Steps to Layout Fire Sprinklers.
We’re starting a new series here on the rules that govern fire sprinkler layouts – particularly when it comes to locations of each sprinkler.
Now this process affects everyone, not just layout technicians.
The layout technician may be the most frequently involved in the layout of the sprinklers, but so too do consultants layout or review sprinklers, plan reviewers, review submittals, installers have to adapt to unforeseen changes in the field, and inspectors are the eyes of the final product.
So, essentially, we’re all invested in knowing this sprinkler layout process.
I’m happy to be with you at this stage. This step is not terribly complex, however, in order to layout sprinklers appropriately we first have to have an understanding for how buildings are constructed, how we categorize obstructed and unobstructed construction, and we have to have an understanding of hazard classifications.
It’s really easy or would be really easy to just sit down with someone brand new, look at a reflected-ceiling plan for say an office space, and just say “hey, sprinklers, no more than 15-ft x 15-ft apart” (or 4.6 x 4.6 meters). You may have heard this yourself, either in teaching someone else or hearing it from someone else.
But there are problems with that approach, because when we do that, we’re making a lot of assumptions with just that quick 15 by 15 statement.
We’re assuming that our sprinklers are Standard Spray sprinklers, that the occupancy hazard classification is Light Hazard, that our ceiling is flat, that we are Unobstructed Construction, and that the system is hydraulically calculated.
What? That's like five assumptions that's built in by just saying 15 by 15 sprinklers. Now, even though that might be the most common case if we're doing light commercial construction, that still doesn't accurately represent how we go about laying sprinklers out.
Let’s dive in and explore this in detail.
LIST OF STEPS
So, what are the steps to lay out fire sprinklers?
1. Determine if a space is supposed to have sprinklers
2. Determine the Hazard Classification for the space
3. Evaluate the ceiling or the roof deck: is it Unobstructed or Obstructed?
4. Evaluate that ceiling or roof deck again: is it Combustible or Noncombustible?
5. Do we have a pipe schedule or hydraulically calculated system?
DON’T MAKE IT HARD
Now Joe, how did you take something so simple, like dropping dots on a page, and make it more complicated than it needs to be?
Well first, I don’t make the rules. I just enforce them.
Second, understanding the process is important here. Small mistakes happen – say when a sprinkler is spaced just a few inches too far from the nearest wall – but when big mistakes happen with sprinkler layout, it’s usually because one of these considerations was ignored or missed. I certainly know that when I've made mistakes in sprinkler layouts, the big ones have been because I skipped ahead or made an assumption that wasn't correct about one of these steps in the process.
So, by sharing this big picture process if you will and understanding how it all comes together correctly, we’re putting together a solid foundation for quality sprinkler layouts in our future.
Third, and it is important here, this sounds a lot harder and more time consuming than it typically is. So much of the light commercial or residential work, which is a considerable portion of the construction industry, will fall under similar situations each time. So it’s not like every room or every space or every new building is a brand new, we have to reinvent the wheel kind of situation. Open office spaces with a suspended ceiling, you know, acoustical ceiling tile, well, that’s often going to be under the same set of rules and layouts are gonna happen very fast.
So, for a majority of our spaces, this process is gonna be familiar and go very, very fast.
Now if we have an early nineteenth century mill that’s being converted to apartments using extended coverage sprinklers, well, that’s when we gotta find our code path and walk that trail a little bit slower. Those scenarios are going to take longer, but we're gonna end up with the correct layout in the end, and that's really what's important.
So, I don't want to discourage you from understanding the whole process. I want you to be informed and also appreciate that the steps, whether you have a very complex situation or a very basic situation, those steps are the same each time when we look to space fire sprinklers.
So, for today, in this module, let’s hit an overview of the steps for a layout.
#1 ARE SPRINKLERS EVEN NEEDED IN THE SPACE?
1. Determine if a space is to have sprinklers to begin with
Now this is based on the standard that we’re in, and it’s the subject of an upcoming video that’s in this series.
NFPA 13 and FM Global Data Sheet 2-0 take a different approach than standards like NFPA 13R and 13D.
The short story is, NFPA 13 states that sprinklers need to be provided throughout unless they are specifically allowed to be omitted by a section in the standard. You have to provide them everywhere unless the standard explicitly says you don't have to provide sprinklers for a specific space.
NFPA 13R and 13D only require sprinklers in locations where fires are known to be deadly. This is aligned with the overall strategy of those standards because those standards are life-saving and not necessarily for property protection.
NFPA 13R and 13D tell us where we need sprinkler protection. And again, that's in the locations where fires end up being deadly. We’ll go into a lot more detail on this in that future segment, but our first step in the layout process is to determine if a space is even going to get sprinklers under the standard that we’re using.
#2 HAZARD CLASSIFICATION
2. Determine the Hazard Classification
Hazard classifications are critically important to the success of a fire sprinkler system – perhaps the most important engineering decision that goes into a suppression system.
We covered this in our earlier series, FX161 on Sprinkler Occupancy Hazard Classifications. We won’t revisit those topics as part of this series.
But in this step what we're trying to get to is - Is our space Light Hazard? Ordinary Hazard Group 1 or 2? Extra Hazard? Some type of storage?
Well, this is our step #2 as part of the layout process. What we're gonna end up with at the end of this step is a hazard classification for each different space.
#3 UNOBSTRUCTED OR OBSTRUCTED?
3. Evaluate the ceiling or roof deck: is it Unobstructed or Obstructed?
This was the focus of two different series that we explored the definitions for Unobstructed and Obstructed. We're not gonna go through all the detail again here but what we need to determine is the ceiling or the roof deck, is it considered unobstructed or obstructed? Does it the way that heat moves up from a fire or water discharges from a sprinkler? Well then that would likely be obstructed. If not, it would be considered unobstructed.
#4 COMBUSTIBLE OR NONCOMBUSTIBLE?
4. Look at that ceiling roof deck again: Is it Combustible or Noncombustible?
Some of the spacing rules for sprinklers, not all of them, but some of them depend on whether we have combustible or noncombustible construction.
A combustible, obstructed ceiling (like say having exposed timbers that are close together) might require a maximum protection area of 130 sqft (12.1 square meters), while a noncombustible obstructed may allow up to 225 sqft (20.9 square meters) per sprinkler. That’s a big difference.
We’ll get into these rules in more detail. But for now, step #4 is to figure out whether the construction type is combustible or non-combustible.
#5 PIPE SCHEDULE OR HYDRAULICALLY CALCULATED?
Is the system pipe schedule or hydraulically calculated?
And if we’re hydraulically calculated and we're in extra hazard or high-piled storage, what is that density?
This impacts us in two ways. First, if we’re under Light Hazard, a hydraulically calculated system instead of pipe schedule will have slightly more lenient spacing criteria. Sprinklers can be further apart.
Now most of the time we’ll be working with hydraulically calculated systems, but what about that density? What was the second point? Why does the density matter?
Well density impacts Extra Hazard and High-Piled Storage spacing. If a sprinkler density is greater than 0.25 gpm/sqft (or 10.2 mm/min), it is afforded less protection area per sprinkler; meaning sprinklers need to be closer together.
#6 SPRINKLER TYPE AND ORIENTATION
6. Now, we select an appropriate sprinkler type.
Upright, pendent sidewall
Standard Spray, Extended Coverage, Residential, CMSA, ESFR or other
Different types of sprinklers are constructed and tested to serve different applications. We could have standard spray, extended coverage, residential, CMSA, ESFR, or other types of sprinklers. We might default to a standard spray sprinkler for a light commercial space, but there are other options available.
If we have decent pressure, perhaps we go with extended coverage sprinklers because those could require less sprinklers overall and potentially less pipe in the system.
If we have residential occupancies, well, residential sprinklers actually have different distribution pattern for water to better fight residential fires. Those hazards are usually along the floors and ceilings. They throw more water up and out to the walls than a standard spray sprinkler. With that benefit, we have some more lenient (or less stringent) calculation methods when we use residential sprinklers and residential occupancies.
What about storage applications like CMSA or ESFR? Well for particular storage setups, CMSA or ESFR can carry better storage flexibility, can allow for more storage flexibility, and better combat fire in those areas. Maybe they prevent needing in-rack sprinklers all together just as one example.
At this Step #6 in the layout process, we are choosing the appropriate sprinkler type for the situation. We’ll cover this in more detail in our series about sprinkler types.
But what about sprinkler orientation? Well, usually, sprinkler orientation is going to be determined by how the ceiling is constructed. Are we protecting below a ceiling where we can conceal pipe that’s located above the ceiling? Well, that means we’re usually gonna have a pendant style sprinkler.
What if there is no ceiling and we have exposed pipe that's below the sprinkler? Well, that would be an upright sprinkler.
What if our pipe isn’t coming from above, but maybe it’s in a wall, or it’s actually fed from the floor below that goes up the wall? Well, that could use a sidewall sprinkler.
The sprinkler orientation is usually dependent on the strategy that we’re going with in the layout. It's usually dependent on the ceiling construction or how the roof deck's constructed.
Then we go to...
#7 SPACING LIMITS
7. Find the limits for sprinkler spacing
Here, we go to NFPA 13 or FM Global and we look at what are the rules?
Now note, an important note is that sometimes there are exceptions to these limits.
As an example, light hazard rooms that are small enough can have small room spacing. The small room rule. This allows rooms that are 800 square feet or less light hazard, a little more leniency for a line of sprinklers.
Also, for storage applications when we have 100 sq ft per sprinkler (or 9 sqm per sprinkler), there are some allowances when we have bays that are 25 feet wide. To extend the distance between sprinklers to allow up to 12 1/2 feet or 3.8 meters between sprinklers instead of 12 feet or 3.7 meters between sprinklers.
This avoids adding a whole additional row of sprinklers in each bay. So, what I'm trying to say is we have the rules and then we also have some exceptions to the rules, and we'll go into that in more detail later.
In the step #7, what we're trying to find out is how much coverage area can a single sprinkler cover?
What is the maximum distance between that sprinkler and the next sprinkler?
What is the minimum distance between that sprinkler and the next sprinkler?
What we're usually gonna dive into NFPA 13 or FM global to find out these limits for our space?
#8 SPOT THE DOT
8. This last step in the process is to actually position the sprinklers
Do the sprinklers meet all of the rules we just laid out? Are they within the limits? Do we avoid obstructions or are they relatively aligned and are they laid out in an efficient manner?
Well, what happens if there’s a large duct, or a surface-mounted light, or a column, or a fan, or a projector, or an exit sign that’s right next to our sprinkler?
Nah that doesn’t happen, Joe. Ok just kidding, it happens all the time. But those are obstructions. After we know all the rules, we still have to pay attention to obstructions and make sure that the sprinkler layout is not adversely affected by those obstructions.
With the sprinkler positioning, we also look to consider layout efficiency and alignment. Do the sprinklers line up in neat rows? Is that wanted as part of the project?
Are the sprinklers relatively evenly spaced? Even spacing helps balance the system just a bit so we can get it more even distribution of water across a floor area. This comes out and helps us out later in the hydraulic calculations.
Now Joe, that’s a whole whirlwind. That's way more complex than I thought it was gonna be. That's a ton to cover. How many times am I gonna have to go back and watch this video? How many times am I gonna go to go step by step and work all the way through this process?
Well, for today, that's our overview. And again, I would say don't be intimidated by this process because once you're familiar with it, you know where to look. When you get into a complex situation, you can follow this step by step and go all the way through. For typical or common situations, this is gonna go very fast. In our next segment, we're gonna take an example and work it all the way through. And then we're gonna talk about the importance of sprinkler spacing, i.e., why you should care, which areas do and don't require sprinklers, the rules for sprinkler spacing, how slope affects spacing, and then we'll do exercises on the topic so we can really sharpen your skill set.
For today? The steps of the layout process are:
1. Determine if a space is to have sprinklers
2. Determine the Hazard Classification
3. Evaluate: Obstructed or Unobstructed?
4. Evaluate: Combustible or Noncombustible?
5. Is the system pipe schedule or hydraulically calculated?
That's all for today. I am Joe Meyer, this is MeyerFire University.
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