Before designing and installing any fire sprinkler system, the occupancy and commodity classifications must be determined for the area to be protected. These classifications are critical to ensuring the system design will provide adequate protection in the event of a fire.
Understanding the occupancy and commodity classifications are important not only for fire inspectors, but also for building owners and facility managers. If the use of a building or a space within it changes, the sprinkler system may no longer provide sufficient protection for that new use. This post will provide an overview of these classifications, including why they matter, and will address a few of the more common questions that arise when evaluating whether a sprinkler system is properly designed for the space it is intended to protect.
Occupancy and commodity classifications are addressed in chapter 5 of the National Fire Protection Association (NFPA) 13 Standard for the Installation of Sprinkler Systems. Occupancy classifications pertain to the use or intended use of a space while commodity classifications are based on the types of materials that may be present in the space. Both factors can have a significant impact on the characteristics of a fire, especially in terms of how hot it will burn and how quickly it might spread, which is why they must be considered when designing a sprinkler system.
All the different factors considered together when determining occupancy and commodity classification will determine the type and number of sprinklers needed, their orientation, and their spacing within a building.
OCCUPANCY CLASSIFICATIONS AND WHAT THEY MEAN
For the purposes of sprinkler design, there are five occupancy classifications, which are defined based on the fire hazards that might be expected in the space:
- Light Hazard — This classification applies to spaces where the quantity of combustibles is low and/or the combustibility of contents is low which would result in relatively low rates of heat release if ignited. Examples of spaces with a light hazard classification might include offices, healthcare facilities, churches, schools, etc.
- Ordinary Hazard (Group 1) — This classification applies to spaces in which the combustibility of materials present is low and the quantity is moderate, with no stockpiles of combustible material exceeding 8 feet (2.4 meters). Examples of spaces with this classification might include mechanical plants, laundries, food processing facilities or other manufacturing operations in which a fire would release moderate rates of heat.
- Ordinary Hazard (Group 2) — This classification applies to spaces where the quantity and combustibility of contents are moderate to high, and which may have stockpiles of materials up to 12 feet high (3.7 meters) that could release moderate rates of heat release if ignited. Examples of this occupancy include distilleries, barns and stables, dry cleaners, libraries, machine rooms, and auto repair shops.
- Extra Hazard (Group 1) — This classification applies to spaces where the quantity and combustibility of contents are very high and dust, lint, or other materials are present, which introduce the probability of fires that burn hot and spread fast, such as upholstery shops, sawmills, plywood manufacturers, or textile factories. This classification may include spaces with some small amounts of combustible or flammable liquids, but the classification is primarily based on the presence of highly combustible solids.
- Extra Hazard (Group 2) — This classification applies to spaces in which moderate to substantial amounts of flammable or combustible liquids are routinely present or where there are large amounts of combustibles, such that the extensive use of heat shields are needed to keep them from igniting. Examples of these include plastic manufacturing operations, steel manufacturing, and automobile paint spray booths.
With regard to occupancy classifications, buildings such as warehouses, which are used primarily for storage, have a separate set of requirements in NFPA 13 based more on the type of commodities they store and the way in which they are stored.
A given space may be classified for more than one of these occupancies depending on its use. If different occupancies are separated such that separate sprinkler systems can be installed, each may be designed based on the individual occupancies. However, when a mixed occupancy exists within the same protected space, the sprinkler system must be designed based on the requirements for the highest occupancy classified to ensure adequate protection.
It is important to note that these occupancy classifications pertain specifically to the design, installation and water supply requirements for sprinkler systems and should not be mistaken for the general hazard classifications identified in NFPA 1 Fire Code and NFPA 101 Life Safety Code requirements.
COMMODITY CLASSIFICATIONS AND WHY THEY MATTER
Sprinkler systems are designed to control or suppress fires in their earliest stages and must be designed and installed for the occupancy they protect. While occupancy classifications help to design for the severity of the fire hazard that sprinklers must protect for, commodity classifications provide additional, more specific information regarding the factors that contribute to that fire hazard.
Commodity classifications in NFPA 13 are based on the type and quantity of materials present in a given occupancy, their packaging, and the types of containers they are stored in. There are five classes of commodities identified in NFPA, including plastics which, due to the high speed and temperatures at which they burn, are further subdivided into three groups:
- Class I — This class includes noncombustible products, such as canned foods, and metal items, packaged and stored in single-layer corrugated cartons.
- Class II — This class includes noncombustible (Class I) products that are stored in combustible containers such as wooden crates and boxes, corrugated cardboard cartons and boxes, waxed-paper containers, etc.
- Class III — This class includes combustible products such as those made of wood, paper, or natural-fiber textiles. Class III also includes Group C plastics and a limited amount of Group A or B plastics (5 percent or less by weight or volume).
- Class IV — This class includes Class I, II, or III products and packaging containing a significant amount of Group A plastics (5-15 percent by weight or 5-25 percent by volume) stored in ordinary corrugated cartons with or without Group A plastic packing, which may be stored with or without the use of pallets.
- Plastics — Plastics are subcategorized into three groups based on the levels of heat they release and the speed at which they burn:
- Group A is the fastest burning and most common type of plastic and includes many of the plastics commonly used in toys, soda bottles, and household products. This Group of plastics burn very quickly and can release more than twice the heat than ordinary combustibles once ignited.
- Group B plastics are soft and pliable such as that found in plastic tubing and products made of nylon. This Group also includes natural rubber, which has similar characteristics in that it burns more slowly than Group A plastics and produce a moderate amount of heat.
- Group C plastics are slow-burning, high-density plastics, such as that used in CPVC pipes and melamine. While these plastics are more difficult to ignite, when they burn, the heat release rate is far greater than that of ordinary combustibles.
It should be noted that the International Fire Code (IFC), 2015 edition also includes a list of classifications for commodities, which differs somewhat from that in the NFPA 13. However, the American Fire Sprinkler Association has pointed out that the IFC is far broader in scope than the NFPA, and that it is more appropriate when addressing overall fire protection requirements for a building. However, when it comes to the design, installation of sprinkler systems specifically, the requirements in NFPA 13 apply.
Not all materials and products fall neatly into one of these commodity classes, but may still pose a potential fire hazard. If you have questions about materials that you are using or storing in your building, you can contact a Koorsen fire control expert at (888) 456-8038 with any questions you might have.
While the term “storage” is self-explanatory, the subject deserves a somewhat detailed consideration in the design of sprinkler systems. The requirements in NFPA 13 pertaining to storage apply to all materials to be stored in a given occupancy, whether they are raw materials, works in process, or finished goods. Therefore, storage includes spaces that may not be routinely considered storage areas, such as production areas. The requirements apply both to storage within the main occupancy and areas incidental to it.
NFPA 13 includes requirements for a number of different storage arrays, including stockpiles, palletized storage, racks (in single, double or multiple rows), shelf storage, and bin boxes, which are metal, wood, or plastic boxes with an open face on the storage aisle. Aisle width and storage height (specifically, the amount of clearance between the top of the storage to the ceiling) are also considered.
Different commodities can be stored in the same storage area. In spaces with mixed commodities, the highest protection requirements will generally apply unless they are isolated such that each type of commodity can be protected with an individual sprinkler system designed for its classification.
Here are a few of the reasons that storage is such an important consideration when designing a sprinkler system:
- Storing materials and products on racks introduce air space around the unit load, which can help a fire grow more quickly within the storage arrangement.
- Bin boxes can present unique fire control challenges because, in the event of a fire, they can capture water from the sprinklers and prevent its even distribution down through the racks.
- Aisles can help slow the spread of fire from one group of materials to an adjacent group by creating a fire break between storage racks or piles and allowing an open area for the sprinklers to fill with water spray.
The slope of the ceilings in the storage is also an important consideration as they can significantly impact average activation time for sprinklers — the higher the slope, the longer it can take for the heat of the fire to activate the sprinkler. The height of the ceilings also matters because fire spreads faster vertically than horizontally, so the amount of force at which water is released must be sufficient to reach the base of the fire.
DOES YOUR SPRINKLER SYSTEM PROVIDE THE PROTECTION YOU NEED?
Your sprinkler system is an integral part of the fire protection system in your building. A system that is not properly designed can result in a major or total loss of your business in the event of a fire.
If you are a building owner or facility manager, you need to know the occupancy and commodity classifications for your sprinkler system to ensure that they match the current use of your building. This is also important if you have any plans for renovation and/or reuse for your structure because they may result in different classifications than your sprinkler system was designed to protect. Something that you might consider a minor change could have a significant impact on the effectiveness of your sprinkler system.
Koorsen can help. Our highly trained and certified sprinkler system experts can assist you with any questions you might have regarding your current system. Contact Koorsen today to ensure your business is protected.