What Hazard Classification for 8-ft Self-Storage?

4/10/2023

I am working on a project with a new client who develops multi-level Self Storage Facilities.

The typical units are 10'x20' with 8-ft bent metal purlin dividing walls. The walls do not extend to the ceiling deck which is 11'-6" above finished floor.

All sorts of household items are being stored, which can include exposed expanded foam mattresses that are greater than 5-ft in height when on their side. The tenants are limited in storage height to 8-ft because of 14 gauge metal wire netting above the units.

On previous projects the client has been permitted to classify the hazard as OH2 (possibly because of the definition in NFPA 13, 5.3.2. 2016 edition, which includes contents with high-heat release rates up to 8-ft).

The question is whether or not it should be Extra Hazard Group 1 or Extra Hazard Group 2?

I am leaning towards EH1.

The occupancy is a storage facility so I believe we fall into Chapter 12 for our design requirements. Because we have exposed expanded plastics stored greater than 5-ft we cannot be considered Low-Piled (Chapter 13). Therefore we fall into Chapter 15.

Using NFPA13 Table 15.2.2.5(a) and the decision tree, selecting plastic commodities, Group A, Expanded, Exposed, Unstable, I believe the Density would be 0.30 gpm/sqft. This would be EH1.

I am using NFPA13, 2016 edition.

Can anyone speak to how they would classify the hazard (design area and density) for this type of storage facility?

Should it be OH2, EH1 or EH2?

Thank you.

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20 Comments

Pete H

4/10/2023 07:47:55 am

EH1 sounds right based on 15.2.2.5(a). Unless they put in shelves (no more than 8'-0" for top of storage) to make it "stable", then you can get down to OH2.

Glenn Berger

4/10/2023 08:19:31 am

The challenge with self-storage facilities is that no one will be policing the actual materials being stored, the actual storage arrangement, etc.

Extra Hazard Group 1 would be the safe bet to use on this project.

Now if you can police the storage then OH2 could be used.

Jesse

4/10/2023 08:28:33 am

We do a lot of these and always design to OH 2 considering it to be misc. storage.

James Phifer

4/10/2023 08:59:42 am

we've completed about a dozen of these self-storage buildings in the last 10 years and have also always used OH 2, miscellaneous storage as the hazard classification. This has always been acceptable to our AHJ, the State Fire Marshal's office.

Eric R

4/10/2023 09:22:36 am

I'll preface this with it's entirely possible that OH2 is more than adequate for this hazard. I don't have any real-life data to argue that it's not.

However, my main problem with OH2 is that there are so many available reductions to overall flow-rate when using it.

With OH2 you "could" choose to install 155F, QR, 5.6K sprinklers and utilizing the QR reduction drop your design area down to 900-1000sqft. You now have a system that only needs 180-200 GPM of overall flow, and would assumingly economically size your pipes to that flow rate. This drastically reduces the density available from you initial head activation, which in turn increases the likelihood of additional heads opening and overwhelming the design as the single sprinkler can't contain the heat release of the 4 Casper mattresses, 3 foam padded couches, and the dozens of thin plastic Walmart storage bins filling the cubicle.

Now as a designer you might choose to go with the full 1500sqft design area, and utilize 286F, SR, 8.0K sprinklers, and with those extra safety factors the 0.20 density may actually work out just fine. However, nothing is stopping your competitor from taking all those allowable reductions and blowing your price out of the water, besides personal risk assessment obviously.

Considering how ubiquitous this building type has become, the fact that we are stuck here having to argue(in a friendly way!) this without access to full-scale burn tests is the real problem. How many thousands of these basically identical buildings have gone up in the last decade across the country. Surely more than other specialty hazards that have benefited from specific burn tests over the years.

Just an AHJ

4/10/2023 09:38:11 am

Great points in this reply. Your AHJ will probably prefer OH1 but I understand the need to win the bid to get the job in the first place. I think it's important to consider how people "organize" things in these storage units. As in...they don't. And they overload them and mix different hazards without a second thought. Someone may very well throw a mattress over the top of an entire unit full of random objects. They fire may be able to grow in size and intensity quickly while the water is blocked by a mattress, tarps, couch, etc. In my opinion it's better to be safer and assume the worst given the element of the unknown items and arrangement to be stored.

4/10/2023 09:47:25 am

I agree with you Eric. we really have no way of knowing what will be stored, in what quantity or in what manner. However, mattresses stored up to 8 ft would still be considered OH2. Since the storage isn't monitored well, we could still get into EH 1 or 2. but as you stated, my competitors aren't going to bid it that way. This needs to be stated by the EOR that they want extra hazard. I'd love to see more testing on this area.

Karl Beck

4/13/2023 08:04:43 am

Excellent post Eric. Regarding the allowable reductions to reduce pipe sizes. At the contractor/designer level, as you know, our job is to provide a compliant system in the most profitable way (not that this all is about money - but I guess it is!). That is why from an engineering (design professional) level, I feel it is important & have always been an advocate of providing (accurate) pipe sizes on bid documents. This levels the playing field for the bidders, and can save a building owner a ton grief. I have always been directed to design these types of storage units as an OH2, but based on your input, I can agree that an EH1 should, at least, be considered. Thank you for your excellent post!

Alex

4/10/2023 08:29:07 am

It seems appropriate to classify the hazard as Extra Hazard Group 1. As you mentioned, since the storage facility has exposed expanded plastic commodities greater than 5-ft in height, it cannot be considered Low-Piled (Chapter 13) and thus falls into Chapter 15.

Following NFPA 13 Table 15.2.2.5(a) and the decision tree, selecting plastic commodities, Group A, Expanded, Exposed, Unstable, you have determined a density of 0.30 gpm/sqft, which falls under EH1.

4/10/2023 08:43:10 am

My quick answer is that EH1 is what I've been using recently for similar projects. I've got three such buildings currently under construction at EH1 using the same code path you described, and all were well received by the AHJs when presented.

My long answer is that I strongly believe that FM Global or the Fire Research Foundation needs to do some burn tests to help identify the best approach to protect this increasingly common occupancy type.

There are two main draw-backs that you get from going with EH1 that may actually lower the overall fire protection performance. The primary one is that the larger design area of 2000/2500 sqft (depending on k-factor or head temp) will necessarily require a trade-off on the overall density you can provide based on your available water supply. A 1500sqft design area could potentially allow you to bump your density higher than 0.30 by utilizing larger K-factor heads without exhausting your available water. Considering that the hazard is already segregated into nice cubicles the idea of dumping more water over a smaller area has a lot of merit.

I did a test design on one of my current projects following the above concept, and I was able to utilize 11.2K heads to get a 0.60 density over a 900 sqft area(based on one head directly over a fire, and the adjacent 8 sprinklers), without having to modify any of my current pipe sizes.

The second draw-back is something I'm less sure on, but the prohibition of not allowing QR sprinklers in EH1 hazards may not be as applicable to the highly segregated storage arrangement of this occupancy type. Having QR heads could be very beneficial especially with the generally lower ceiling heights in these multi-floor structures.

The concept of larger K-factors with quicker response times, discharging a higher density over a smaller design area seems to make logical sense to me based on how segregated a self-storage hazard is. However, without full-scale burn testing being performed it is hard to be certain that I'm not missing something in this analysis. Would love to get more feedback from others here on this theoretical approach!

Again EH1 sounds like a good place to be for now at least!

Carson B

4/10/2023 12:01:43 pm

I'm in agreement. I think it should be EH1. As mentioned by others, it boils down to money and bids.

I'm curious why the definition of Ordinary Hazard (Group 2) NFPA 13, 5.3.2. (2016) is defined as"...stockpiles of contents with high rates of heat release do not exceed 8ft."

Seems to me that the definition of OH2 should be "high rates of heat release do not exceed 5ft."

A5.3 states "For purposes of these definitions, Class I, Class II,
Class III, and Class IV commodities would be considered to
have moderate rates of heat release, while Group A plastics
would be considered to have high rates of heat release."

When looking at Storage of Group A Plastics, if you are over 5ft, you move up to Extra Hazard.

So why 8ft?

Casey Milhorn

4/10/2023 09:15:23 am

We see OH2 almost every single time from the EOR. I would love for NFPA or FM to perform some testing and a study on this. I think ceiling heights and construction type play a huge role in this. Most of the conditioned mutli-level stuff we see has approx. 10' to 11' deck heights, and typically mesh installed at 8' to limit the storage height. I would have to imagine that activation is going to happen very quickly and uniformly over the areas with heat release. I'm no expert, but I would have a hard time believing that the area would involve more than a few 10x10 units (so maybe 300 sqft). To go to EH we are talking (25) 10x10 units being involved which seems very unlikely. Construction type is almost always metal skinned walls to 8' or 9', C channel metal construction for walls and supports, and concrete. A lot of the data in the storage sections of NFPA 13 is derived from storage with deck heights much higher than 10'+/-.
On the downside, those units do get packed extremely tight many times, with lots of obstruction to water spray.
Again, I think the key would be a smaller design area (max 1500 sqft), but high density, using ELO QR sprinklers (as Eric mentioned).
Great question and discussion!

Dan Wilder

4/10/2023 09:17:06 am

The last couple we have bid, we bid for EH1 with an alternate to lower to OHII with AHJ approval (typically an owner's letter).

If the AHJ is involved and somewhat knowledgeable, or recently experienced a loss, they typically ask for a letter from the owner about storage allowances and limitations and have that info put on the plans for the lesser density (both the fire sprinkler and the code analysis pages). If they just don't know, we see a lot of OHII with a maxed 10x13 layout and smaller lines....those are the ones we don't win contracts on.

Will it work....possibly, but not something we would take on liability for just to win a bid.

Zack H

4/10/2023 09:38:36 am

I did one of these recently and made an assumption that why mattresses are Group A expanded that mattresses and other expanded plastics were likely to be less than 25% of the total commodities. So, per Figure 5.6.3.3.3 (b) you would be able to still classify the commodity as Group A unexpanded. This would then move you to column A of Table 15.2.2.5 (a) and a .2/2500 density. Our AHJ was happy with this approach considering that they were typically approving OH2 in the past.

4/10/2023 12:40:22 pm

This is very good, and a strong argument to go with OH2 - 0.2/2500 density. It may actually prevent the need for a fire pump in some scenarios where the municipal water has low pressure.

However, based on NFPA 13, 15.2.2.9 you would still have to apply the installation requirements for extra hazard systems (100 SF) for storage of Group A plastics between 5 ft and 12 ft in height. I think this has been left out of the discussion so far.

4/10/2023 03:10:23 pm

After looking at Chapter 5 of NFPA 13 (2016) for a bit, I dont believe we can classify the "fire area" based on percentage of commodity types.

Fire Areas should be considered based on the Highest commodity, i.e. Foam Mattresses - Reference 5.6.1.2 Mixed Commodities

5.6.1.2.1 states - "Protection requirements shall not be based on the overall commodity mix in a fire area."

5.6.1.2.2 Unless the requirements of 5.6.1.2.3 or 5.6.1.2.4 are
met, mixed commodity storage shall be protected by the requirements for the highest classified commodity and storage arrangement.

We do not meet the requirements of 5.6.1.2.3 or 5.6.1.2.4.

Correct me if i'm wrong, but Figure 5.6.3.3.(b) is in reference to classifying a Product (not a fire area) containing a mixture of Expanded and Unexpanded plastics.

I think what's confusing is the conditions to classify a (III, IV or Unexpanded Group A Plastic) product that contains Expanded Group A plastic are dependent on the product's environment. The environment being either Cartoned or Exposed. That makes it confusing to me. Reference 5.6.3.3.3, 5.6.3.4.1 (7), or 5.6.4.1.1.2(6).

Products that are classified as Class III, IV, and Unexpanded Group A - that contain a mix of Exposed Group A Plastics within the product, can still be considered the lower classification if they meet Figure 5.6.3.3.3(B).

So I think were back to classifying it as Extra Hazard Group 1.

4/10/2023 10:16:17 am

To add one more bit of complexity to the discussion.

A decade ago when I did my first few self-storage designs the building's structural framework was either full I-beam, or I-beam/truss combination construction. Some even used to get fire-proofing sprayed on them.

Today, two of the buildings I have under construction are supported by load bearing walls made entirely of 2x4 light gauge metal framing, with not a single piece of heavy steel anywhere in the building.

I'll leave the math on how much quicker the light gauge metal framing will fail under heating to our resident FPEs, but I'm relatively confident it's not identical to traditional steel beams.

So we have a situation where over the last decade combustibility of commodities has increased while framing materials have become more light weight. Feels pretty comparable to the well documented issue of residential home fires and TJI/Truss construction leading to rapid collapse.

Anthony

4/11/2023 07:11:12 am

Just another thought to the OH2 Vs EH1. The walls between each unit could be cinderblock and have an effective 2 hr rating or could be corrugated metal with no rating. That may help you choose between the 2 solutions.

James Art, FPE

4/12/2023 11:39:45 am

NOT in California:

Regarding Eric's response that mentions a reduction in area for
Q/R based on height:

This may be one reason that in Ca. that reduction is ONLY available for Light Hazard, NOT for Ordinary Hazard, or greater.

See the Ca. changes in CaFC Chapter 80, or in CaBC Chapter 25.

4/12/2023 07:33:21 pm

The intent of the reduced area was to encourage the use of QR sprinklers in OH hazards. Light hazard was just a logical beneficiary of this reduced area rule.

So at one time, QR sprinklers were actually a "new technology" and they were required to be used in light hazard areas. The benefits of having QR sprinklers (their ability to activate quickly and therefore help control/extinguish the fire sooner) were noticed and the reduced area rule was made to encourage them to also be used in OH areas. They were actually more expensive at the time than standard response. Well it didn't make sense to allow reduced area for OH but not for LH.

You could argue that the reduced area has outlived it's usefulness and it's time to make QR sprinklers required in all OH areas as well. Then the debate would be if 900 sqft should be the new norm (if it meets the parameters in NFPA 13) or if 1500 sqft should be the norm. I would argue that if 900 sqft was acceptable for X amount of years, then it should continue to be unless there is evidence to contradict that.

I strongly disagree with AHJs making their own rules such as CA. They usually don't understand the history or the testing that went into these exceptions, allowances, etc... or the consequences of these decisions (like discouraging the use of QR sprinklers in OH areas). Anyway, that's my two cents on it.

What Hazard Classification for 8-ft Self-Storage?

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