In my regular code calls I used to include a specific question on the use of clean agent systems in server rooms.
Building Owners & Sprinklers
Many building owners provide clean agent systems to extinguish fires in high-value content areas, such as server rooms, data centers, archival storage, and many other applications.
When the owners voluntarily pony-up for extra protection in these areas, they often ask whether sprinklers have to be installed in those spaces at all.
My Code Call Question
On my code calls, my question would go something like: “does your jurisdiction require sprinklers to be installed in rooms which are protected by a clean agent system?”
I would get a mixed response. Some jurisdictions considered clean agent systems to be an equivalent for sprinkler protection, others would not.
A couple years after asking this question on every applicable project I had a fire marshal shoot me straight.
“If you don’t have sprinklers in the room, you don’t have a fully-sprinklered building. Check the IBC.”
This was news to me. I was under the impression that use of clean agent systems could be used as a substitute for fire sprinklers and still be effectively “fully-sprinklered”.
Back to the Book
There is a path for this approach – the International Building Code (2018) Section 904.2 states that:
“Automatic fire-extinguishing systems (ie: clean agent) installed as an alternative to the required automatic sprinkler systems of Section 903 shall be approved by the fire code official.”
This was the foundation on which I had been asking the question.
The big kicker was the code section just a paragraph later:
“904.2.1 Restriction on using automatic sprinkler system exceptions or reductions. Automatic fire-extinguishing systems shall not be considered alternatives for the purposes of exceptions or reductions allowed for automatic sprinkler systems or by other requirements of this code.”
Outside of the lawyer-phrasing, this section simply states “no sprinklers in the room – no sprinkler reductions or exceptions for your building.”
The commentary by the International Code Council goes further, stating that while the authority has the ability to approve alternative systems in lieu of sprinklers, doing so invalidates the “fully-sprinklered” status of a building.
Why Does this Matter?
Why is this important? There is a long list of code kickbacks that sprinklers offer a building.
A couple months ago I diagramed a cheatsheet for all of the major code benefits a “fully-sprinklered” NFPA 13 fire sprinkler system offers. You can download it free here.
Code benefits include allowable building heights, building areas, number of stories, egress benefits, passive rating reductions, Draftstopping reductions, fire alarm reductions, and a handful of other benefits.
I realized after that code call that the question affected well more than just my isolated “fire sprinkler” silo. Omitting sprinklers in just one server room would have code implications throughout the complex.
Now, should building owners ask about omitting in these rooms we often look at other strategies – such as concealed sidewall sprinklers, use of dry sprinklers, drip pans, use of pre-action systems, or piping without joints and heavy-duty cages. Some of these solutions can be painless, without great cost and satisfy code as well.
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I was asked recently for a specific project how much flow the owner should anticipate coming from a building's main drain.
There's just a few factors that play into exactly how much water to expect. Is the drain serving as the main drain for a system? Is it only serving an inspector's test? Is the drain off a 1-inch pipe, or 2-inch? How much pressure is on the system?
These aren't often difficult to answer if you're familiar with the job, but each of these answers plays a role in determining how much water will come out of an open orifice.
This week I've simplified a few of these parameters to come up with a quick inspector's test and drain calculator for fire sprinkler systems.
With it, you can estimate the amount of flow that will come from an inspector's test (use the k-factor option) or from a drain (diameter option). For our international audience I have incorporated real units from the get-go this time. It's a free tool that's now live on the site, here.
Give it a spin and let me know what you think in the comments here.
Know others that might find this helpful? Send them a link or tell them to subscribe here.
Thanks & have a great week!
Over a year ago I released a Thrust Block Calculator online.
It that takes a small handful of inputs and offers sizing and dimensions according to NFPA 13. The tool has been a reasonable hit except for one repeated request from the field – the thrust block weight. Until now designers and engineers using the tool still had to convert the minimum required volume into the minimum weight based on the density of the concrete. Hand calc no longer!
Special thanks to Sinisa who offered the reminder after I asked for pet peeves or upgrade requests in last week’s post.
If you’ve never used the tool and would like to check it out, here’s the link to it. It's free and available now.
Last item for this week - I'm circling back to a call for water storage tank experts. If you're experienced in this space and would like to review a new tool I'm working on, please shoot me an email at email@example.com. Would be happy to set up beta testing.
Thanks and I hope you have a great rest of your week!
If you know someone taking the PE Exam this week, it's time to give them a hug. Maybe not an actual hug; don't be a creeper, but maybe a kind supportive attaboy wouldn't be a bad idea.
Final Call for the PE Exam
This Friday is the day for the 2019 Fire Protection PE Exam... the same exam that at least two hundred fire protection professionals have been honing in on the past few months.
This year marks the last year of the written examination. Major changes are on the horizon for the Fire Protection PE in 2020, including question style, references, and going to a computer-based environment. The biggest change may be that no longer will any resource be allowed in the exam room. There'll be plenty to cover on the 2020 exam later on.
Perhaps because of the big looming changes, we've seen a major uptick around here in the interest in the Fire Protection PE Exam. I would guess that this year will set the record for the number of examinees. That's a great thing. I'm thrilled that the fire protection industry as a whole is growing, and I hear almost weekly about how rare Fire Protection Engineers are in our industry.
What is the PE Exam?
For those who don't know, the PE Exam is the Principles and Practice of Engineering examination which is administered by the National Council of Examiners for Engineering and Surveying (NCEES). The exam is the major milestone to getting a license to practice as a Professional Engineer in the United States. In order to take the PE Exam, examinees must typically first complete a four-year ABET accredited engineering program and a Fundamentals of Engineering (FE) Exam as well as accruing four years of experience working with a licensed engineer. Of course the requirements vary by state but that is the most common requirement.
Last Minute Exam Advice
If you have a copy of the Prep Guide you already know there's quite a bit of detail on exam advice passed down through the years included in the book.
Regardless of how many hours you've spent studying (whether two or two hundred), there will always be topics that are over-emphasized, poorly worded questions, and niche questions that seem to have no basis in any reference materials. Keep calm and exam on! Skip and come back to questions later. Some of these questions are just on trial for future exams and others will get disputed and thrown out. All you can do is your best. Don't worry about surprises you can't control but focus on what you know and give it your best effort. Best of luck, you've got this!
Updates for 2020 PE Exam
If you have sent in information on the 2019 Edition for suggestions or potential updates, thank you! With all that's happened around here this summer I haven't been as responsive to PE Exam emails as I've tried to be in the past. Please know that I go through all of these and make updates for future examinees, and I greatly appreciate your time in sending suggestions in.
New Feature on Quick-Response Remote Area Reduction
I've had a pet peeve about one of my own tools. Awhile back I created a calculator that will determine the allowable reduction in the hydraulically remote area based on the use of quick response sprinklers. It's a quick-hitter and one I use often.
Each time I use it, though, I still end up using the reduced area and punching in 1.2 times the square root of the new area in order to lay out my hydraulically remote area.
Being that I'm all about convenience (ie: laziness) and efficiency, I've now added that basic calculation in the tool as well. You can see the new feature here.
If you have similar nuances on how these tools can be improved, let me know! I'm always happy to entertain new ideas. You can always reach me at firstname.lastname@example.org.
Have a great week!
Some big news on the MeyerFire front –
With the growth of the community here at meyerfire.com, I’ll be transitioning next week to support this venture full-time and begin my own design practice.
This is a very big and exciting step for me, and I cannot express how thankful I am to have you be a part of the community here. It is because of your support and interest that’s made this possible.
This week’s quick post is a collection of Q&As that I’ve gotten recently that I’m happy to share.
What’s different now?
Two big developments have come through in the last couple months.
You may have noticed the website sponsorships that started in September. There is a good handful of interested organizations that serve the same audience and want to support our efforts at MeyerFire. Sharing their message has helped open up time I can contribute to site resources. I'd encourage you to click sponsor's messages as I both vet and have personal connections with each sponsor organization.
The second big development is still in the works. It involves a major publication with a renowned fire sprinkler organization. I’ll be sure to relay information in time, but for now I’m excited to partner with an expert group and help bring more resources to the industry. This should be a complete volume by the middle of next year.
Will the website change?
Since July I’ve spent about 8 hours a week on the site. That includes developing content, writing for the blog, developing tools, helping Toolkit users, and supporting PE Examinees. This shift to full-time independence will open the potential to increase support for all these things. My hope is that you’ll continue to get better content and more useful tools with every new post.
So this whole website thing is a lead-magnet for your design practice?
Nope. MeyerFire.com will stay and keep the name and continue on where it is.
I’ll continue to design because it’s what I love to do and it keeps me firmly entrenched in the industry’s hot issues. While it will launch this upcoming Monday the 21st, the new website for the design side of things will be www.MeyerFPE.com. My intent is to focus in on only a few specific small-business clients and support them extremely well. It’s also not my intent to hire any employees (see last week’s I’m terrible at management article). Of course business is fluid and change is constant, but that’s my initial intent.
So How Much You Makin’ Off This-Here Website?
When I started writing regularly about two years ago, I had about twenty subscribers. I would guess half of them had my last name. If I looked I would have bet three of them were just different emails my mom used.
Since then (due to your support and sharing posts on LinkedIn & Facebook), the number of subscribers has grown dramatically. Those first few months in 2017 I was over the moon when three new people subscribed on the month. Now, somedays, there will be a dozen or so new interested professionals each day. It’s never about how many people tune in but about the impact of sharing best practices. The growth is well on the up and up and the distribution now approaches that of some of the leading fire protection organizations. You’ve made that possible and I can’t thank you enough for it.
So money - the three revenue sources, if you will, are website sponsorships, PE Exam Prep content, and the Toolkit software package. The site sponsorships have just kicked off in September and have lots of interest. The PE Prep Guide is now technically the bestselling Fire Protection PE Exam book on the market, and there are now over 200 active MeyerFire Toolkit users.
All of this combined still doesn’t make up a full-time income, but the impact that the combined effort is having has been incredibly positive. Not pursuing these in greater capacity would be something I’d otherwise live to regret.
A Few Notes
The transition to full time developer is a big step and a big transition for me and my family. It’s not without a lot of thought, nervousness, and a lot of excitement. Of course this is all really the beginning, but there are several people I’d like to thank just making it to this point.
I’d like to thank the incredible team at SSC Engineering in St. Louis. They have a supportive and sharp group and I am so fortunate to have learned under the best these past few years. If you’re ever in the market for MEP, FP, or Structural design services, I would recommend the crew wholeheartedly.
I’d like to thank some bigtime supporters and mentors for me. Far too many people to name, but those that have really stood out over the years are Mike Auld, Drew Robinson, Adam Hilton, Cindy Gier, Jeff Dunkel, Chris Cornett, Angie Grant, David Stacy, Aaron Johnson, Ed Long, and Mike Lonigro. You all rock.
I'd also like to thank YOU for being a part of this community and being an advocate for better fire protection. I’m excited about what we’re going to build together.
Earlier this summer at a conference I met up with my first supervisor out of college.
I say supervisor because he hated the term “boss” and worked hard to be a good leader.
He was super-sharp, very driven, and very focused on his long-term goals. I admire all those things about him. Sidenote: he doesn’t know this blog exists, so don’t spill the beans : )
He gave me advice when I was a few years in that I still am extremely thankful he offered.
He told me to not leave design too early.
There’s a natural career path for talented professionals that points to management. It can happen quickly and naturally. If we're not careful, the jump can go right into a role where we are no longer growing our technical depth.
A great entry-level designer is one that is eager to learn and mature.
In time, that designer will work more complex projects, collect some credentials, and serve clients & managers well.
A promotion (informal or formal) can lead to more interaction with customers and project management.
The shift happens slowly, but it's real. It can be easy to get caught up in proposals, mentoring, estimating, business development, managing people, or in a myriad of other tasks.
This is not a bad way to go. It's just not in design.
Great designers can become great project managers and great leaders of companies. The world needs great leaders.
The point my supervisor made was that if I’m not careful, the “blessing” of getting into management early in my career could lead to a shallow technical foundation.
Our value as designers and engineers is based on our ability to serve others with quality, timely help. Once someone shifts from a technical-first role and into a management-first role that technical depth is hard to maintain.
It was timely and important advice.
For some time I debated pursuing an MBA degree. I chose graduate study in fire protection engineering instead. What I began to recognize was that there is a tremendous and unique value to having a technical skillset.
I switched to a new company in 2016 and since then have dabbled in mid-level management. My role has been to grow a small team in fire protection by mentoring and teaching what I know.
I learned that I am terrible at it.
All through high school and college, it seemed that every target was pointed towards the C-Suite. Leadership organizations in particular placed the prized goal as “executive” status with a company.
I think my parents and their generation sees the “executive” concept as having the most glory. I found management to be closer to a mix of babysitting and life coaching than the glamour of Don Draper in Mad Men.
Leadership involves a lot of things that don’t come naturally to me.
I don’t particularly like rules or accepting past practices at face value. I tend to enjoy operating independently and challenging standards. I really don’t like standards. To clarify - I don't mean NFPA 13 or building codes. I love those little guys. I mean company standards. I tend to not give directions well and I’m also terrible at taking the time I should to help champion others.
These things don’t lend to great management.
What I also learned was that every hour spent managing, proposal writing, or sitting in meetings was an hour I didn’t spend learning.
After some time I made a choice.
I chose to be deliberate about staying in design.
I want to be in the weeds. I want to come across questions that stump me. I want to ask questions. I want to model systems and stocklist and do seismic calculations. I enjoy those things.
The unique value we have as fire protection designers & engineers is the technical understanding we have. We understand systems that help save lives. There’s a real and unique value in that.
If a company is looking for management material, they have options. There are six-hundred US MBA graduates for every one Fire Protection Engineer. Six hundred for every one.
When I first heard the advice, I didn’t know the value that a graduate degree in fire protection would bring to my career. I didn’t realize the wild demand that this industry would have for great designers & engineers. I also didn’t know that I’m pretty awful at managing.
My only advice I can pass forward is to always be sure you’re deliberate about the path you want to pursue.
It is a great goal if you want to pursue management.
A very close friend of mine wants to be CEO of a particular major corporation. I’m pretty sure he’s dreamed about it since he was a kid the way my sister pretend-played weddings. That’s a great and noble goal.
It’s also great if you choose to stick to design and be an expert in it.
We need leaders that can grow and share their technical understanding.
Just be deliberate about the path you take. It’s far too easy to drift and find yourself in a role where you no longer share your greatest talent with the world.
I'll come out and say it.
I’m a millennial.
I like to think I can opt out of millennial status voluntarily, but I'm told it doesn't work like that. Technicalities…
I like to think that the relentless pursuit of finding better & faster ways to do better work is about innovation and constant improvement. I guess it could also just be considered finding ways to avoid work or wanting the "apps" to do any real engineering.
Today's post covers one of my favorite cheats on checking site elevations and distances. It's super easy and a major benefit when setting up or reviewing hydraulic calculations.
On a side note I'm also told that the kids these days call these "hacks". I'm told that a "hack" is a good thing, so I'll roll with it. Besides - age is just a state of mind, right? I'm cool, I promise. Just don't ask my kids.
Here's the “hack” - just follow these steps:
Get Elevations Between Any Two Points
1. Open Google Maps (https://www.google.com/maps)
2. Enter or zoom in on any address.
3. Right click on any location you wish to get an elevation on. Select "Directions to here"
4. Now right click on any location at least a block away, such as your tap for the building's water connection. Select "Directions from here"
5. Now you'll have opened up the directions dialogue. Instead of car directions, click on the walker icon in white at the top.
6. Click on the very bottom description in gray. It often reads “Mostly Flat”. This opens up an elevation view from your original point (such as your building’s water tap) to your building. This shows your end elevation (against sea level), your original elevation, and the elevation difference between the two.
Measuring Site Distances
While still in google maps, you can also get distances on a site.
Here's a video showing both (click this link if you don't see the video):
Earlier this year I had a project I was reviewing which showed no elevation difference between the flow test and the base of the project. The pipe distance was roughly accounted for, but no elevation.
I checked the test distance on Google Maps and despite only being several hundred feed from the project, the test was at an elevation 32 feet lower than the base of the project.
Did this affect the hydraulic calculations? It absolutely did. The calculations went from having 6 psi safety to being 8 psi over the available water supply.
The measurement tool comes in handy for many projects where site plans are not prepared. This doesn't come up quite as much in new construction, but certainly for retrofits or projects with no site work - a site plan often isn't available. Use of quick measurements can give some guidance towards using conservative measurements for hydraulic calculations.
If you already knew these two tricks, congratulations, you’re probably also a millennial.
If you didn’t, and would like to send money for the gobs and gobs of time these simple tools will save you in the future, please make the check out to “Joe’s Beer Fund.” Actually better yet – just tell another friend about this site. It is always very much appreciated! Hope you have a great rest of your week.
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!
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Joseph Meyer, PE, is a Fire Protection Engineer in St. Louis, Missouri. See bio on About page.