What is the "small room" rule?

In conducting plan reviews or fire sprinkler field inspections you may have heard, or seen, the invocation of the “small room" rule. Though not specifically stated in NFPA 13 as the “small room" rule, it is a combination of several code sections within the standard that can be utilized to provide advantages in hydraulic calculations and flexibility in sprinkler spacing.

To apply the small room rule, the space must meet all the requirements of a small room as defined in NFPA 13. A “small room” is a space that is classified as light hazard, has unobstructed ceiling construction, and is no greater than 800 sq.ft.  Application of the small room rule will affect two critical system design elements, maximum area of protection and sprinkler spacing.

The normal method for determining the area of protection per sprinkler head is to use the formula:

As = S x L

In this case the distance between sprinklers along a branch line (S) and the distance between branch lines (L) is determined and then multiplied to establish the “maximum allowable protection area of coverage for a sprinkler” (As).  The small room allowances of Section 8.6.2.1.2 permits the sprinkler designer to ignore the rules and requirements of the S x L formula. Instead, an alternate method is allowed. If the space meets the requirements for a small room, then maximum coverage area per sprinkler can be determined by simply dividing the area of the room by the total number of sprinklers in the room.

Sprinkler spacing and distance between individual sprinklers is calculated using the tables and guidance in Section 8.6.3. In these tables, the maximum spacing distance for sprinklers is 15 feet between sprinklers and 7.5 feet from a wall. Utilizing the small room rule requirements, allows sprinklers to be spaced up 9 feet from any single wall.

The small room rule can be stated as:

In a room of 800 sq.ft. or less, having unobstructed ceiling construction, and light hazard contents, sprinklers may be located up to 9’ from any single wall with the maximum area of coverage being determined by dividing the size of the room by the number of sprinklers.

Code summary for small room rule:

NFPA 13:3.3.22 - small room defined

NFPA 13:8.6.2.1 - max. area of coverage

NFPA 13:8.6.3..4 - sprinkler spacing from a wall

Fire Sprinkler Design Guide [for AHJ's]

This interactive guide, and book, will enable the fire plan reviewer or inspector to quickly answer the most important questions for approval and acceptance of a fire sprinkler system.

• Does the structure require a fire sprinkler system?
• Is the occupancy and commodity properly classified?
• Are plastics properly identified and protected?
• Does the rack storage need in-rack sprinklers?
• Will there be any obstructions to the discharge pattern?
• How are the cloud ceilings protected?

Clicking on the title for each section will take you to a full article on the topic. Before you get started, I recommend you download and print my glossary of "Key Terms  for NFPA 13 Storage". This convenient tool eliminates the need to search multiple pages for clarifications by listing the most used terms and definitions on a single page. 

Sprinklers where required…

Reading through the NFPA standards, one consistently comes upon the phrase "sprinklers where required".  However, in order to find where they are, or may be, required, involves some searching through the code book.  

The below is a tool that can be used as a quick guide to what occupancies require fire sprinklers, and where the code can be referenced.

Download the sprinkler requirements guide.

Guide to NFPA 13 Occupancy and Commodity Classifications

Perhaps you are conducting a fire inspection or survey and you notice that the hazard or commodity classification on the hydraulic calculation plate at the riser seems odd for the actual contents of the structure.  Or, you are sitting down to do a plan review, the occupancy hazard and commodity class is listed. Are these classifications correct based on the use of the structure?

NFPA 13, Standard for the Installation of Sprinkler Systems, chapter five defines occupancy hazard and commodities classifications for the design and installation of sprinkler systems. In book form, this information can sometimes be difficult to recall. This slideshow presentation can be utilized as a reference to quickly review and confirm occupancy and commodity classifications.

Download the slideshare cheat sheet.

What kind of plastic is it?

To provide effective fire sprinkler protection within a structure, the hazard classification and commodity must be known. For the protection of rack storage, the storage and shelving configuration must be known. Due to the high speed and temperature of burning plastics, they require special consideration.  NFPA 13, Standard for the Installation of Sprinkler Systems, requires all plastics, elastomers, and rubber, to be classified as Group A, Group B, or Group C.

Fire Protection Requirements for Rack Storage

What are the requirements for rack storage? Are in-rack sprinklers required? How can rack storage sprinkler requirements be determined?

Fire protection requirements for rack storage are addressed in NFPA 13, Standard for the Installation of Sprinkler Systems.  

• Chapter 13, Protection of Miscellaneous and Low-Piled Storage
• Chapter 14, Protection for Palletized, Solid-Piled, Bin Box, Shelf, or Back-to-Back Shelf Storage of Class I through Class IV Commodities
• Chapter 15, Protection for Palletized, Solid-Piled, Bin Box, Shelf, or Back-to-Back Shelf Storage of Plastic and Rubber Commodities
• Chapter 16, Protection of Rack Storage of Class I through Class IV Commodities
• Chapter 17, Protection of Rack Storage of Plastic and Rubber Commodities

To determine which chapter to go to for fire protection requirements, there are three questions that must be answered:

1. What is stored?
2. How is it stored?
3. How high is it stored?

Sprinkler Obstructions and Discharge Patterns

Important to fire sprinkler effectiveness is sprinkler discharge pattern development. A fire sprinkler system should be designed in a manner that provides full water coverage from the fire sprinkler system. Inherent building construction or design elements can pose potential obstructions to the full coverage or discharge pattern of the sprinkler system.  However, these buildings and elements must still be protected. NFPA 13, Standard for the Installation of Sprinkler Systems, provides sprinkler coverage guidance for these obstructed areas.

To determine the proper application it must first be determined if the construction is obstructed or unobstructed.  Then it must be determined if the obstruction is continuous or noncontinuous.

Protecting the Cloud

Cloud ceiling: a suspended ceiling that covers only a portion of a room or space below

These cloud ceilings present unique challenges to fire sprinkler installation. The solution to these challenges are not always easily found clearly in the pages of NFPA 13. However, by applying the obstruction and clearance principles the solution will make itself clear.

What is the "small room" rule?
In conducting plan reviews or fire sprinkler field inspections you may have heard, or seen, the invocation of the “small room" rule. Though not specifically stated in NFPA 13 as the “small room" rule, it is a combination of several code sections within the standard that can be utilized to provide advantages in hydraulic calculations and flexibility in sprinkler spacing.

BONUS: Doorway to Hell - An Analysis of Potential Fire Sprinkler Performance

In 1984 tragedy struck the Great Adventure theme park when 8 teenagers were killed in the Haunted Castle attraction.  The fire, believed (not proven) to have been started by a an individual playing with a lighter, has seen a great deal of controversy, and differing of opinions, through out the years. The resulting code changes created the special amusement requirements in NFPA 101.  

In this video, Jack Fairchild, a certified fire protection specialist with Ballinger A/E, discusses the history and impact of this fire, and guides us through his analysis of the potential effectiveness of fire sprinkler systems, he answers the question, "Would sprinklers have saved these kids?"

What kind of plastic is it?

To provide effective fire sprinkler protection within a structure, the hazard classification and commodity must be known. For the protection of rack storage, the storage and shelving configuration must be known. Due to the high speed and temperature of burning plastics, they require special consideration.  NFPA 13, Standard for the Installation of Sprinkler Systems, requires all plastics, elastomers, and rubber, to be classified as Group A, Group B, or Group C.

A complete list of Group A plastics is provided in 5.6.4.1 and Table A.5.6.4.1, of NFPA 13. This group of plastics includes rubber, poly(s)-, cellulosics, and nylon. Group A plastics are further divided into expanded or unexpanded. Expanded plastics are “low-density materials” commonly referred to as “foam plastics”. Unexpanded plastics must meet one, of six, criteria listed in listed in section 5.6.4..1.1.2. Group B plastics include chloro-, fluoro-, and silicone products. There are seven materials classified as Group C plastics.  This group include the polyvinyl- products. A complete list is provided in section 5.6.4.3.

Sprinkler design criteria for the protection of plastics is outlined in Chapter 15 and Chapter 17 of NFPA 13. If the plastics are Group A and do not exceed 5 feet in height then the protection requirements of Chapter 13, Protection of Miscellaneous and Low-Piled Storage, can apply. For all plastic or rubber commodities that exceed 5 feet in height, section 15.2.2 outlines the fire protection requirements. For clarity and protection requirements the decision tree provided in figure 15.2.2.1 of this standard should be referenced.

If the stored items are plastic or rubber commodities and on rack storage the protection requirements of Chapter 17 shall be enforced. This section has a decision tree that must be followed based on the group of plastics being protected, as well as alternate provisions for systems that do not meet minimum design requirements. If plastic or rubber commodities on rack storage is encountered, this chapter should be closely examined.  

Fire Protection Requirements for Rack Storage

What are the requirements for rack storage? Are in-rack sprinklers required? How can rack storage sprinkler requirements be determined?

Fire protection requirements for rack storage are addressed in NFPA 13, Standard for the Installation of Sprinkler Systems.  

• Chapter 13, Protection of Miscellaneous and Low-Piled Storage
• Chapter 14, Protection for Palletized, Solid-Piled, Bin Box, Shelf, or Back-to-Back Shelf Storage of Class I through Class IV Commodities
• Chapter 15, Protection for Palletized, Solid-Piled, Bin Box, Shelf, or Back-to-Back Shelf Storage of Plastic and Rubber Commodities
• Chapter 16, Protection of Rack Storage of Class I through Class IV Commodities
• Chapter 17, Protection of Rack Storage of Plastic and Rubber Commodities

To determine which chapter to go to for fire protection requirements, there are three questions that must be answered:

1. What is stored?
2. How is it stored?
3. How high is it stored?

“What is stored” refers to the items hazard and commodity classification. “How is it stored” refers to the storage method, or medium (pallets, bins, etc.), and container type (wood, plastic, etc.).  “How high is it stored” refers to the height of stored items.

If the stored items are classified as miscellaneous or low-piled, refer to Chapter 13 for fire protection requirements. “Miscellaneous storage”  does not exceed 12 feet and is incidental to the occupancy (see, 13:3.9.1.18 for additional requirements). “Low-piled storage” is storage that is up to 12 feet in height.  Storage medium for low-piled storage can include, solid-piled, palletized, rack storage, bin box, and shelf storage. Fire sprinkler design requirements are outlined in section 13.2.

If the stored items are classified as a Class I through Class IV commodity, and palletized, solid-piled, bin box, shelf, or back-to-back shelf storage Chapter 14 requirements apply. Fire protection requirements will vary based on height of stored items. Sprinkler design requirements for storage up to 12 feet is outlined in section 14.2.3. Storage over 12 feet is defined in section 14.2.4. It is in Chapter 14 that we first see “encapsulated” storage. This refers to items that are wrapped in plastic sheeting, or pallets that are covered with plastic sheeting. If encapsulated storage is utilized and it is between 15-20 feet, the sprinkler design requirements of section 14.2.5 should be followed.

If the stored items and rack shelving are classified as plastic or rubber commodities, and palletized, solid-piled, bin box, shelf, or back-to-back shelf storage Chapter 15 requirements apply. If the plastics are Group A and do not exceed 5 feet in height then the protection requirements of Chapter 13 can apply. For all plastic or rubber commodities that exceed 5 feet in height, section 15.2.2 outlines the fire protection requirements. For clarity and protection requirements the decision tree provided in figure 15.2.2.1 of this standard should be referenced.

If the stored items are a Class I through Class IV commodity and on rack storage the protection criteria of Chapter 16 shall be met. If these commodities are stored up to 25 feet in height the sprinkler requirements or section 16.2 are to be met.  If the they are stored over 25 feet high, section 16.3 should be followed for protection requirements and design criteria.  If the overhead sprinkler system does not meet the minimum design requirements for protection of the commodity alternate provisions and options are provided in section 16.1.2.4.

If the stored items are plastic or rubber commodities and on rack storage the protection requirements of Chapter 17 shall be enforced. This section has a decision tree that must be followed based on the group of plastics being protected, as well as alternate provisions for systems that do not meet minimum design requirements. If plastic or rubber commodities on rack storage is encountered, this chapter should be closely examined.  The plastic or rubber commodity should be further broken down by answering the original three questions: what type of plastic is stored? How is this plastic or rubber stored? How high is the plastic or rubber stored?  Fire protection requirements and design criteria will differ based on the answers to these questions.

Sprinkler Obstructions and Discharge Patterns

photo source: pmengineer.com

Important to fire sprinkler effectiveness is sprinkler discharge pattern development. A fire sprinkler system should be designed in a manner that provides full water coverage from the fire sprinkler system. Inherent building construction or design elements can pose potential obstructions to the full coverage or discharge pattern of the sprinkler system.  However, these buildings and elements must still be protected. NFPA 13, Standard for the Installation of Sprinkler Systems, provides sprinkler coverage guidance for these obstructed areas.

To determine the proper application it must first be determined if the construction is obstructed or unobstructed.  Then it must be determined if the obstruction is continuous or noncontinuous.

Is this obstructed or unobstructed construction?

To be considered obstructed, the construction elements must be composed of “beams, trusses, or other members” that will impede heat flow, water distribution, or otherwise affect the ability of the sprinkler to control or suppress the fire. [13:3.7.1]

Construction types that may create obstructions, include:

• Beam and girder
• Concrete Tee
• Composite wood joist
• Panel construction
• Bar joist with fireproofing
• Steel purlin

Unobstructed construction includes any “beams, trusses, or other members” that do not impede heat flow, water distribution or the ability of the fire sprinkler to control or suppress fire. This generally consists of construction members that are not solid.[13:3.7.2]

Unobstructed construction elements may include:

• Bar joist
• Open-grid ceilings
• Smooth ceilings
• Standard mill (heavy timber)

Is the obstruction continuous or noncontinuous?

If the obstruction affects the sprinkler discharge pattern of two or more adjacent sprinklers then the obstruction is considered to be continuous. However, if only one sprinkler discharge pattern is affected then the obstruction is noncontinuous.

Different sprinkler head types and orientations have different requirements for designing to protect obstructed areas.  These are addressed in the following sections of NFPA 13.

• General guidance: 13:8.5.5
• Pendant and upright sprinklers: 13:8.6.5
• Sidewall sprinklers: 13:8.7.5
• ESFR sprinklers: 13:8.12.5

A great reference tool for quickly determining the design criteria and requirements for obstructed areas is this ceiling obstructions reference tool/calculator provided by Meyer Fire.

13 Changes to NFPA 13

As the newest edition of NFPA 13 is set to be presented next month, NFPA has published some of the notable changes to this document:

1. CPVC compatibility - where corrosion inhibitors are used in combination systems that include coated steel pipe and CPVC pipe, the coating must be tested for compatibility with CPVC.
2. Freeze protection requirements - tentative interim amendments regarding antifreeze solution to prevent the freezing of water in sprinkler pipes has been formally adopted into the standard
3. Sprinkler requirements for elevator spaces and hoistways - allows fire sprinklers to be omitted from elevator machine rooms, elevator machinery spaces, control spaces, or hoistways of traction elevators where a number of conditions are met, and brings the standard in alignment with other model building codes
4. Title change to NFPA 13R - Standard for the Installation of Sprinkler Systems in Low-Rise Residential Occupancies
5. Sprinkler protection in small bathrooms - Apartment buildings with bathrooms less than 55 square feet (5 square meters) must now have sprinkler protection where they were not  previously required to do so.
6. Shadow areas -  shadow areas are permitted in the protection area of a sprinkler as long as they do not exceed 15 square feet per sprinkler.
7. 
   "Sprinkler system" definition - modified to describe a system as an integrated network of piping that includes a water supply source, a water control valve, a water flow alarm, and a drain; this largely effects the requirements of NFPA 25.
8. Backflow preventer requirements - a forward flow test will now be required on all NFPA 13/13R installations.
9. Storage chapter - newly added; allows for an alternative design approach.
10. Sloped ceilings - provides five common ceiling arrangements that allow for hydraulic calculations
11. Water mist systems - refers users to NFPA 750.
12. Cloud ceilings - protection to follow the use of obstruction rules.
13. ESFR and CMSA sprinklers - these will now be permitted to protect light and ordinary hazard areas.