FPE Extra Issue 1, January 2016

Research Leads to Important Changes to NFPA 13

By Ken Isman, P.E., FSFPE

The 2016 edition of NFPA 13 has been published and it contains hundreds of changes from the 2013 edition. Many of these changes are small, intended to clarify existing text or refine language so that everyone understands the intent. But a significant number of changes in this cycle utilized research results to shed light on completely new subjects and expand the reach of NFPA 13 into areas where the standard was silent in the past. In most cases, the research responsible for these changes was sponsored by the Fire Protection Research Foundation (FPRF) specifically to provide needed answers to questions that would enable the committee to reach an informed consensus.

This article is not a comprehensive list of all of the changes that have occurred in NFPA 13 (other organizations make such lists available). Instead, this article focuses on those changes that have made a significant impact, blazing new ground in NFPA 13 through research and analysis efforts.

Cloud Ceilings and Concealed Spaces

Prior to the 2016 edition, cloud ceilings were not defined within the NFPA system of codes and standards, but the term was used by architects to describe a space with a drop ceiling that covered only part of the floor area. That drop ceiling could be at a single elevation or at multiple elevations and might cover anywhere from 1% to 90% of the floor area of the room. The name “cloud ceilings” comes from the idea that these partial drop ceilings look like little islands in the sky as you look up from the floor, like clouds seen from the ground.

The question regarding cloud ceilings is always whether two (or more) layers of sprinklers are necessary (above and below the clouds), or whether a single layer of sprinklers is sufficient. There are many variations of the question depending on the size and location of the clouds. A room with a drop ceiling over 90% of the space with gaps only at the walls is an example of a situation where a sprinkler system designer might want to only put sprinklers under the drop ceiling. But would a fire at the wall create a problem for the structural members above the drop ceiling with no sprinklers at the higher level?

At the other end of the spectrum is the room with a high ceiling and one cloud 5 ft x 5 ft (1.5m x 1.5m) in area suspended 4 ft (1.2m) below the upper ceiling. With sprinklers directly under the upper ceiling, would an additional sprinkler be needed under the cloud?  How could you get pipe to that sprinkler and would it look decent? These are the types of questions that needed to be addressed by NFPA 13.

Prior to the 2016 edition, NFPA 13 did not specifically address cloud ceilings, but this did not mean that the standard completely ignored the subject either. Three sections in the older editions of NFPA 13 applied to cloud ceilings: section 8.1.1 required sprinklers in all areas, section 8.6.5 required sprinklers under obstructions more than 4 ft wide and section 8.15.23 required that when a room had more than one ceiling, sprinklers be installed between the two ceilings unless the space met the concept of a concealed space. So, putting these sections together, a solution could be found for cloud ceilings, but it was not one that necessarily always made sense or made architects happy.

The FPRF sponsored a research project that is not entirely complete yet, but has begun to yield results. This project looked at the concepts of cloud ceilings and the similar issue of defining what a “concealed space” would be (since there has been no definition of a concealed space in NFPA 13). Traditionally, concealed spaces have been considered those spaces that are completely closed off from surrounding spaces by some form of construction, but the committee has clarified that small openings, such as those found for return air for a plenum are permitted without forcing the space to be considered something other than “concealed.”

The FPRF efforts considered a number of different configurations of cloud ceilings and concealed spaces and subjected them to an analysis of what is likely to happen during a fire. The results have led to the following list of changes to NFPA 13 that ensure that a sprinkler system performs its function while offering architects and design engineers more flexibility in their design:

1. Definition of Cloud Ceiling - Any ceiling system installed in the same plane with horizontal openings to the structure above on all sides. This does not include sloped ceilings as defined in

2. Openings in Concealed Spaces – A new section allows concealed spaces of noncombustible and limited combustible construction to have openings that are 20% or less of the floor area of the room. If the opening is going to be more than 4 ft (1.2m) long, it cannot be more than 8 inches (20cm) wide. This permits the space above a drop ceiling to be considered a concealed space and omit sprinklers without having to call the space a “cloud ceiling.”

3.      8.15.24 Cloud Ceiling Rules – A new section has been added to permit sprinklers to be omitted from above cloud ceilings even if the space is not considered a “concealed” space. A table provides information on the maximum size opening that is permitted based on the height of the drop ceiling. This is based on FPRF work that showed that as the fire plume rose, the plume spread out sufficiently so that sprinklers under the drop ceiling would respond in time to control the fire and prevent damage above the drop ceiling where there were no sprinklers. As the ceiling height increases, the allowable gap gets larger. A number of other rules apply including the use of quick response sprinklers or extended coverage sprinklers limited to 16 ft between sprinklers under the cloud ceiling.

4. Area Reduction for Use of Quick Response Sprinklers – For many cycles, NFPA 13 has permitted a reduction in the design area in light and ordinary hazard occupancies when quick response sprinklers are being used. Starting with the 2016 edition, this reduction will not be permitted when sprinklers are omitted from above a drop ceiling in accordance with section 8.15.24 as discussed above. Note that this only applies to the drop ceiling rules. If sprinklers are omitted from a concealed space with openings as described in section, the reduction for the use of quick response sprinklers is still permitted.

Exposed Expanded Plastics Stored on Racks

Ever since the days of NFPA 231C, the NFPA standards have been silent on how to protect rack storage of exposed expanded plastics. Users have been told that definitive test criteria has not been presented to the NFPA committee, therefore the NFPA standard cannot recommend discharge criteria.

Thanks to a research project from the FPRF that included full-scale fire testing, the 2016 edition of NFPA 13 contains criteria for the first time on how to protect exposed expanded plastics on racks. Two new sections have been added to Chapter 17: section to cover storage 25 ft (7.6m) in height or less and section to cover storage over 25 ft (7.6m) in height.

The new protection criteria consists of intermediate temperature K-25.2 (KM-360) ESFR sprinklers at the ceiling and vertical barriers in some of the transverse flue spaces extended from near the floor to the top of storage. These vertical barriers stop the horizontal spread of fire down the rack structure and focus the heat of the fire towards the ceiling, helping sprinklers to open earlier in the fire scenario. The discharge criteria will be 12 sprinklers operating at 60 psi (4.1 bar). Storage up to 35 ft in (10.7m) height will be able to be protected with these criteria in buildings up to 40 ft (12.2m) in height. See sections and for more information on how to construct the barrier and other limitations such as aisle width.

Commodity Classifications

The key to a successful sprinkler system design is to define the commodity correctly. From this decision, all other portions of NFPA 13 follow, including sprinkler selection, sprinkler spacing, and discharge criteria. For the 2016 edition of the standard, the committee made a number of changes to Chapter 5 and its associated annex to help users of the standard properly define what sort of storage commodity they would be dealing with.

This is the only item in this article that was not the subject of research by the FPRF. Instead, the NFPA Committee on Sprinkler System Discharge Criteria appointed a Task Group to review known literature and make appropriate recommendations for change. This Task Group spent countless hours digging up information on how different materials burn and presenting that information in a consistent and usable manner. The following is a summary of these changes:

1. Class III – The definition of a Class III commodity was modified regarding the amount of plastic that could be included without requiring higher classification. Under the old rules, a Class III commodity could have up to 5% plastic by weight or by volume and it did not matter whether the plastic was expanded or non-expanded. Under the new rules, you have to use the weight to evaluate the unexpanded plastic and the volume to evaluate the expanded plastic. The limit is still 5% in both cases.

2. Class IV – The definition of a Class IV commodity was modified regarding the amount of plastic that could be included without requiring a higher classification. The amount of plastic will depend on whether the commodity is in cartons or is exposed and whether the plastic is expanded, non-expanded, or a mixture of expanded and non-expanded material. If the material is a mixture of expanded and non-expanded products, figures have been added to Chapter 5 to define whether the object can be considered as a Class IV commodity or whether it needs to be treated as unexpanded Group A or expanded Group A plastic.

3.      Table A.5.6 Commodities Not Addressed – The list of examples of commodities that cannot be classified as Class I-IV or Group A plastic has been expanded to include items like carpet rolls, lithium-ion batteries and fireworks.

4.      Table A. Guide to Identifying Commodities – A new table has been added to the annex to help the user understand what the committee has in mind for each of the commodity classifications.

5.      Table A.5.6.3 Alphabetical Listing of Commodities – This existing table has been expanded and corrected given what is known today about how items typically burn. This is the first wholesale update of the table since it was first introduced in the 1998 editions of NFPA 231 and 231C.

This article merely scratches the surface of the changes to the 2016 edition of NFPA 13. The focus here has been to examine the most impactful changes that have used science, analysis and research to expand the boundaries of what we can protect, and shed light on old questions that either had no answer or produced answers that were difficult for users to deal with.

Each of these new sections in NFPA 13 is a beginning of an approach to protecting these challenges, but not an end. The research is ongoing. More arrangements of cloud ceilings will need to be explored. New combinations of sprinklers and other fire protection features may be found that will protect exposed expanded plastics stored on racks. This is one of the reasons that NFPA standards are revised on a regular basis, so that new research can be incorporated into the standard. As it stands now, the 2016 edition of NFPA 13 represents the most up-to-date application of research, science and analysis, and jurisdictions should start referencing it as soon as possible to take advantage of these advancements in knowledge.

Ken Isman is with University of Maryland’s Department of Fire Protection Engineering.

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