Last week I discussed a common question in residential construction concerning whether NFPA 13R could be used, or whether NFPA 13 had to be used.
If you haven't read it, you might check it out. Here's a link.
The four global limitations to using NFPA 13R include:
The last qualifier is often the most difficult to assess, and is an important question that the architect or code consultant for the building will need to answer.
To help determine whether a building can use NFPA 13R, here's a PDF cheatsheet that shows differences in code allowances using NFPA 13, 13R, 13D, and no protection at all.
All of the references are to the International Building Code 2018 Edition, but this should help offer some quick guidance on different code allowances to check for your project. As always, it's worth using this as a starting point and then exploring the code nuances to be sure your project is up to snuff.
If you haven't already subscribed - you can do so here. This blog is all about promoting best practices in fire protection by providing tools, resources, and helpful articles.
Travis Mack at AFSA
If you're going to AFSA's Conference in San Diego next week, be sure to check out Travis Mack's presentation on this topic. He's an industry leader & expert in everything suppression.
Correction on the Porte-Cochere Logic
A couple weeks ago I discussed the differences between different forms of heat transfer in the context of flame spread. I made a point that conductive heat transfer is the least critical of the three forms of heat transfer, but suggested that fires "jump" across roadways due only to radiation heat transfer. This is due primarily to convective heat transfer - strong winds can promote fire growth far faster than radiative heat transfer can - and it often does for large wildfires.
I mentioned last week - but I'm down to about a dozen copies of the 2019 PE Prep Guide Edition left for the year. If you know someone who is looking for a copy you might suggest they get it sooner rather than later.
Thanks & have a great week!
For the contractor clients I work with I regularly look over jobs pre-bid. I’ll review drawings, read specifications, and compile all my notes looking for red flags that could impact the job from a design standpoint. (The cheatsheets that I use to breakdown a job is now all in the Toolkit)
Last month I reviewed an apartment complex job for a bid where the code summary had conflicts. The IBC Chapter 5 summary indicated and NFPA 13 system while the IBC Chapter 9 indicated an NFPA 13R system. There were no other references to a fire sprinkler system in the rest of the documents or specifications.
These are the projects that I blame my hair loss on. It's another bad example of project documentation. Regardless, the question of NFPA 13 versus NFPA 13R is something that comes up regularly and is the topic of this and next week's article.
Why Does it Matter?
NFPA 13R is not built with the same intent as an NFPA 13 system.
NFPA 13R systems are designed to “prevent flashover (total involvement) in the room of fire origin”. By doing so, they intend to improve the ability for occupants to survive a fire by evacuation. 13R design is primarily concerned with protecting areas of residential buildings where fires cause loss of life. It is not as concerned with fires in areas where fatal fires in residential occupancies do not originate. (Reference IBC 903.3.1.2 Annex)
NFPA 13 systems, however, intend to provide a “reasonable degree of protection for life and property”. In a general sense, NFPA 13 systems are concerned with both life safety and property protection. The goal is to suppress a fire near its' point of origin, regardless of the level of risk to life safety.
Cost can be largely impacted by the NFPA 13 vs. NFPA 13R decision -
especially in wood construction buildings with attic spaces and overhangs.
Aside from having different purposes, NFPA 13 vs. 13R decisions can have major implications on system cost.
NPFA 13R systems allow sprinkler omission in a handful of areas which 13 does not. These include small closets, exterior balcony closets, concealed spaces, elevator machine rooms, garages, carports, attached porches, and attic spaces. I've summarized these with a cheatsheet here.
For wood-construction (a mainstay in residential design), attic sprinkler systems under NFPA 13 can command a major cost premium. These attic systems need dry valves, air compressors, use of steel in lieu of CPVC, special application sprinklers, and design requirements that can require large diameter pipe.
Testing and maintenance is also a long-term ownership concern. Not only do dry attic systems require regular low-point drainage, but they often corrode faster than wet systems .
Attic systems are one area of a building that can be a huge difference between NFPA 13 and 13R.
That said, I’ve also worked on projects where 13R has little to no impact on the project price. A flat-roof building built with non-combustible structure, for instance, offers no major difference. The only impact was the lower density permitted for residential-style sprinklers. Using the 0.05 gpm/sqft in lieu of 0.10 gpm/sqft of NFPA 13 resulted in smaller pipe diameters for an NFPA 13R system.
Buildings must be residential, four stories or less, 60 feet in height or less,
and not use any code exemptions for an NFPA 13 system in order to use NFPA 13R.
When Can I Use NFPA 13R?
There are four global limitations where an NFPA 13R system can be used. These include:
"My project is design/build with deferred submittals. Can’t the contractor determine this?"
No - and I can’t stress this enough – please do not leave this determination to a contractor.
It doesn’t matter if you’re an architect, mechanical engineer, or the expert code consultant. There are a number of code exceptions that can only practically be determined by the design team. The sprinkler contractor is an expert on suppression – not on architectural design decisions and the code paths for those decisions.
What are the building code exemptions that require an NFPA 13 system?
The code exceptions show up for building height increases, building area increases, egress widths, travel distance limitations, occupancy separations, corridor wall ratings, hazardous material increases, inclusion of atriums, unlimited area buildings, allowable area of openings, vertical separation of openings, draftstopping, interior finishes, floor finishes, manual fire alarm systems, and several others.
Sounds like a lot? It is. Fortunately I’ve got a cheatsheet coming next week where I’ll explore these differences in more detail. If you’re interested in getting a copy, subscribe here and it’ll be emailed directly to you.
A couple weeks I posted a link on this month’s sponsor Engineered Corrosion Solution’s whitepapers. Many of you have already checked it out, but if you haven't there's a MeyerFire welcome page here: https://www.ecscorrosion.com/meyerfire-welcome
I had a couple people ask about the whitepapers, so here’s a direct link to them. Specifically, be sure to check out "Industry Myths Regarding Corrosion in Fire Sprinkler Systems" and "Six Reasons Why Galvanized Steel Piping Should NOT be used in Dry and Preaction Fire Sprinkler Systems."
PE Prep Guide 2019 Selling Out
There's been a ton of interest this year in the PE Prep Guide. I genuinely appreciate every single person who's checked out the book for this year's exam - there has been more interest than ever before and I suspect the exam turnout could be the most ever for the Fire Protection P.E. Exam.
Next year's exam in 2020 will go computer-based and have major changes, so the PE Prep Guide will undergo big changes as well. This year's shipment of the 2019 Edition is just about out, and because of the big changes next year I won't be ordering extra copies. We currently have 16 copies available, so the 2019 edition will likely sell out by October's PE Exam. If you'd like to get a copy of the 2019 PE Prep Guide, please consider doing so now.
After the 2019 Edition sells out we'll still have 2018 PE Prep Guides available, and I'll ship an errata list with it. Any questions, please reach out to me at email@example.com.
Last week I discussed across a common misconception with porte-cochere sprinkler requirements and how code addresses sprinkler protection for these structures.
This week I’m diving a little deeper with some estimates of how a porte-cochere fire would actually affect a main building, based on distance from the building.
It’s important to note that this exercise is largely academic: with the calculations below I’m making some gross assumptions that overly simplify the situation. This has not been vetted with Ph.D. experts nor gone through full scale fire testing. I’m just running some basic numbers with big assumptions to illustrate a point.
From what science gives us - heat is transferred by three methods. Conduction, convection, and radiation.
Conduction is the transfer of heat by objects touching each other. The direction of transfer is dictated by hot-to-cooler materials in direct contact.
Convection is the transfer of heat caused by the movement of gas (or a fluid). The direction of transfer is largely dictated by overall movement of the fluid, and for smoke tends to be vertical.
Radiation is the transfer of heat from the emission of electromagnetic waves. The direction of transfer is in all directions, but can reflect and re-emit from other surfaces.
Heat Transfer for a Flame
For a flame, depending on the fuel, most of the heat will be transferred away from the flame source primarily by convection. The chemical reaction (oxidation) of a flame will cause gases to heat. The heated gas’ molecules will become more active and less dense. With less-dense gas than surrounding cooler air, the warm gas will rise up and away from the flame source and carry solid particles forming hot smoke.
Radiation will typically comprise 20-35% of the overall heat release rate for a fire. Radiation transfers heat from the source in all available directions until it contacts another surface. Once in contact with other surfaces, radiation can be absorbed or re-emitted from the surface, depending on the surface material.
Conduction is the least important mode of heat transfer in an open fire. Radiation near a flame’s origin, for example, often emits and heats up adjacent surfaces with more impact than conduction. For wall assemblies, conduction of heat through penetrations becomes important, but for flames in open environments conduction plays only a small role.
Three Porte Cochere Scenarios
Now imagine a porte-cochere that is 100 feet (30 m) from the face of a larger main building to the center of the porte-cochere. If the porte-cochere is completely inflamed, how would it transfer heat to the main building?
It would transfer heat only by radiation; and in very small amounts. Assumptions include a 5 megawatt (MW) fire from a wood-built porte-cochere, a 100-foot (30 m) center distance from the main building, an atmospheric transmissivity of 0.95, and a 30% of the overall heat loss as radiation.
Using the Lawson and Quintiere Point-Source Method, the incident radiant flux (a measure of the heat energy per area) is 0.13 kW/sqm.
This radiant flux is about 10% of the flux for a 1st degree burn on unprotected skin.
Now move the porte-cochere to be 30 feet from the face of the building. Radiation will again transfer heat to the face of the building, but in a much larger amount. Because radiant flux is related to the inverse square of the distance between the targets, this 30-foot distance will actually have a radiant heat flux 10 times greater than a porte-cochere fire 100 feet away. For the same size fire as before but at 30-feet, this could be about enough heat for a 1st degree burn.
At the 30-foot distance, however, heat transfer to the main building is still primarily by radiation. The hot, buoyant smoke is still primarily driven upward from the porte-cochere and would likely not reach the main building unless strong winds directed the hot gases.
Now imagine this same porte-cochere, but this time centered only 10 feet (3 m) from the main building. Radiation heat transfer is now 10 times greater than the 30-foot distance, and 100 times greater than the 100-foot distance.
At only 10 feet from a 5 MW fire, the heat flux is enough easily cause 2nd degree burns for unprotected skin.
Additionally, this heat flux is now approaching the critical heat flux for ignition of some building materials. The critical heat flux is the minimum amount of heat, per area, required to cause ignition. There's several factors that contribute to ignition including exposure time, material thermal properties, surface temperatures, and the actual heat flux versus critical heat flux - but for our purposes I'm only showing this critical heat flux for a couple siding materials.
Wood, for instance, has been tested to have a critical heat flux of approximately 10 kW/sqm. Vinyl siding has a critical heat flux of approximately 15 kW/sqm (both values from SFPE Handbook of Fire Protection Engineering, Table A.35, 5th Volume).
When we look at the heat flux already produced by a fire of this size at 10 feet we can see that we're already approaching the critical heat flux for both wood and vinyl.
Now let's speak in practicality. Porte-cocheres are built to allow visitors to enter and leave cars without exposure to rain or sun. Is a 30-foot or 100-foot separated porte-cochere provide any value to a building? No, of course not. This exercise just shows that with reasonable assumptions, a 10-foot physical separation assuming a 5 MW fire begins to approach the critical flux needed to ignite a nearby building.
Would the actual fire be 5 MW? It's difficult to predict and will vary widely by the materials used and the shape it conforms. A point-source approximation is a large oversimplification given that a wooden canopy would burn in a very different configuration than a condensed pile of wood pallets, for instance.
What about convection? Up to now we've still only discussed heat transfer by radiation. If a porte-cochere is close enough to a building, convective heat transfer from the hot smoke will begin to contact the main building and heat surfaces along the face of the main building. This could also be aided by wind conditions as well.
As I explored a little last week, a porte-cochere that is only separated inches or a couple feet from a building is hardly any different than a porte-cochere that's attached to the building. That's largely because of convective and radiative heat transfer. The further away the porte-cochere is, the less convective heat transfer plays a role and the lower amount of radiative heat will be transferred.
What if we create a firewall or fire barrier? Both would slow the spread of fire and help prevent the main building from burning. The International Building Code relaxes the physical separation with fire-resistive construction, and for good reason. Heat flux becomes much less important when the exterior is of non-combustible construction.
It can be easy to get lost in code minutiae and live by the black and white lines of what code reads. I find that it's important to remind myself about context about each building and where good engineering judgement plays a role in protecting buildings from fire.
This overly-simplified series of calculations just shows the tiers of radiative heat transfer and how much it is affected by the separation distance. The further away a building is from another, the less convective heat transfer plays a role (if any) and the less radiative heat transfer occurs.
If you found this interesting, let me know by leaving a comment here. Always happy to hear other opinions. If you don't already follow the weekly blog, consider subscribing here. Thanks for reading!
In February of last year I put together a flowchart that covered sprinkler requirements for exterior projections. If I had a Top-10 Articles list, it'd be on it.
If you haven’t read it,here’s a link to the original article.
Since I wrote this article and posted the original flowchart, I’ve received some encouraging feedback and thoughtful comments.
I’ve updated the flow chart this week to address specifically sprinkler protection of porte-cocheres:
What's a Porte-Cochere?
First, because I have no idea where the term “porte-cochere” originated, I’m talking about the covered entrance where vehicles can pass through as part of an entranceway to a building.
Not to point fingers, but I’m guessing the term “porte-cochere” was dreamed up by an architect to disguise the fact that they’re sticking a carport on the front of their building. Maybe it’s my Missouri roots, but what we’re talking about here are just fancy carports that can be driven through. Now stepping down from the soapbox…
"If It's Not Touching the Building..."
Stop me if you've heard this one before.
One common assumption I’ve heard repeatedly from architects and contractors concerning porte-cocheres is that sprinkler protection isn’t required for porte-cocheres if they are not connected to the main building.
Unfortunately, that's not justified by code.
It is true that porte-cocheres, on their own, often do not require fire sprinkler protection. They will generally fall under a Type U (Utility and Miscellaneous Group) Occupancy, which do not require fire sprinklers by IBC 903.2.
However, in order to qualify as a separate “building”, the International Building Code requires a physical space separation, a fire-rated separation, or a combination of both.
In terms of a porte-cochere attached to a main building, the porte-cochere would be considered a separate building by any one of the following:
As an example, if the main building is a Type V-B (combustible construction), Residential R-2 Occupancy (such as a Senior Living facility with more than 16 people), then the minimum requirements for a porte-cochere as a separate building would be:
From a practical standpoint, what is the difference between a porte-cochere that’s six inches from the main building and one that is touching the main building?
None. Zero difference.
I’ll explore this from a scientific perspective in next week’s article, but in short - conduction heat transfer makes little difference in the spread of fire from one structure to another.
Want to know why forest fires can “jump” across highways? It’s not because trees are locking branches above roadways – it’s because of radiative heat transfer.
So why do we get so tied to the concept that if the porte-cochere isn’t touching the main building that it’s as if it doesn’t exit? I’m not sure exactly, but it seems to come up quite frequently.
One Note on Concealed Spaces
NFPA 13 has two separate sections that affect porte-cocheres. The first is protection below overhangs, canopies, & porte-cocheres. This article and the flowchart address this situation. The second section is protection within concealed spaces.
If your porte-cochere does not require sprinkler protection per the building code, then no sprinklers are required regardless.
If that's not the case, and your porte-cochere has concealed spaces within it, check out NFPA 13's Special Situations section to see if the concealed spaces require sprinkler protection. These may still be required to be protected even when sprinklers can be omitted below the ceiling. This show ups in Section 8.14.1 of the 2002 Edition, Section 8.15.1 in the 2007-2016 Editions, and Section 9.3.18 in the 2019 Edition.
Losing the Forest for the Trees
I sometimes find that when assessing code it is easy to lose the forest for the trees.
Sometimes I can be so fixated on finding one specific answer that it is easy to step back and assess the ‘big picture’. Addressing overhangs and canopies can get that way.
While I don’t always get the opportunity to address fire protection intent with a building owner, I have to keep in mind that code only prescribes the minimum requirements. We can always elect to improve fire protection & life safety above code minimum.
Two recent local fires come to mind when looking at how sprinkler protection affects overhangs and how different owners were impacted very differently.
The first fire occurred at an apartment complex when a tenant left a lit cigarette on the third story balcony of an apartment complex. The cigarette started a fire on the unprotected balcony, which spread into the apartment attic (without draftstops) and quickly spread across the attic of the entire building. The upper two levels were badly damaged along with the entire attic and roof needing replacement.
Another fire occurred, more recently, at a three-story office with a porte-cochere. A car fire underneath the porte-cochere activated a single sprinkler which suppressed growth until the fire department arrived. The porte-cochere had smoke damage, but the fire had no impact to the main building. No downtime, no multi-million dollar rebuild. From the photos it was difficult to see any impact from just inside the main entrance.
These are two different situations of course; the first likely an NFPA 13R and the second an NFPA 13 system. Nonetheless it raises the issue of making sure that we, as professionals, inform and have dialogue with the building owner to not just determine what code minimums require, but what levels of protection may serve them best.
This Month's Sponsor
I'd like to introduce this month's MeyerFire sponsor with Engineered Corrosion Solutions. They are experts in the corrosion space for fire sprinkler systems and have a long list of helpful resources on their website.
As a side note, some of their original whitepapers and case studies were instrumental for me in my understanding of current corrosion challenges. When should we specify galvanized pipe? Is MIC or oxygen-induced corrosion a bigger concern? What can we do to stop corrosion entirely? They have it all here.
Thanks to the ECS team for helping promote this site and supporting my efforts to develop new resources for the industry.
Next week I'll explore the concept of porte-cochere separation distance, but from a modeling perspective. How much does the distance impact radiative heat transfer? How does convective heat transfer play a role? I'll explore this in more detail and from a calculated perspective next week.
If you don’t already get these weekly articles via email, subscribe here. If you know someone who might be interested, please pass a link along. Thanks and have a great week!
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Joseph Meyer, PE, owns/operates his own Fire Protection Engineering practice in St. Louis, Missouri. See bio on About page.