October 18 2021 0Comment
Storage warehouse fire protection

Factors of Fire Protection – Storage Occupancy

Storage Racks

Businesses of nearly every type store some kind of product or stock material in their buildings. The materials in these storage spaces range depending on your particular business and could include everything from raw materials and finished goods to paper files. Storage areas can be considered small designated areas inside a building or they can be large warehouse facilities solely dedicated for storage and retrieval of goods and materials.  

According to NFPA 101 Chapter 42; Storage Occupancies shall include all buildings or structures used primary for the storage or sheltering of goods, merchandise, products or vehicles.

Regardless of what is being stored, traditional storage spaces such as warehouses or even the most unassuming storage room can present a unique fire control challenge.  For most situations, fire control would consist of a fire sprinkler system. A fire sprinkler system in its basic terms is a system designed to control or suppress a fire in its earliest stages, utilizing a limited number of operating sprinklers. However, it is critical that these fire sprinkler systems are properly designed and installed for the storage they are protecting.  Storage occupancies, the type of commodity being stored and the manner in which they are stored are vital factors to unveiling the demands required for each particular system.

Three Critical Factors should be taken into consideration when evaluating your fire prevention methods:

  1. Commodity Classification — classification based on the type of product stored, including container and packaging materials.
  2. Storage Arrangement — whether the product is stored in racks or piles or on pallets, the type of shelving, clearance to the roof, aisle width, etc.
  3. Storage Height — maximum height of storage in relation to the height of your building.

Commodity Classification

There are five basic commodity classes. These classes range from metals to plastics, with plastics being the most difficult to protect. The basic commodity classes are:

  • Class I: noncombustible products in single-layer corrugated cartons such as noncombustible liquids in glass containers, canned food, ice cream and metal parts
  • Class II: Class I products in slatted wood crates, wood boxes, multiple layered corrugated cartons, waxed-paper containers or equivalent packaging
  • Class III: wood, paper, natural-fiber cloth or Group C plastics and a limited amount of Group A or B plastics (5 percent or less by weight or volume)
  • Class IV: Class I, II or III products containing a significant amount of Group A plastics (5 to 15 percent by weight or 5 to 25 percent by volume) in ordinary corrugated cartons; Class I, II and III products in corrugated cartons with Group A plastic packing, with or without pallets
  • Plastics: This commodity class is subcategorized into three main groups which helps to assess the rate at which the plastic commodity would burn.    
  • Group A — the fastest burning and the most common; includes many of the plastics commonly used in toys and household products.
    • Group B — burns moderately and is less common; includes nylon and natural rubber.
    • Group C — the slowest burning; products such as CPVC and melamine.

There are many types of materials and products, some of which that may not fall into one of the above commodity classifications that also pose severe fire hazards. If you are uncertain as which classification and group your particular storage commodity falls into, it is best to discuss with your local fire official or trusted fire prevention expert.

Warehouse storage1

Storage Arrangements

Product can be stored in a variety of arrangements also known as arrays. Each array has specific protection requirements that are affected by physical characteristics such as aisle and flue space as well as the location of shelving and obstructions to water penetration.  Some of these common storage arrays are:

  • Solid Pile Storage

Stacked commodity stored directly on the floor.

  • Palletized Storage

Stacked commodity stored on pallets, on the floor, or on other pallet loads.

  • Single Racks

No more than 6 feet deep with a minimum aisle width of 3.5 feet.

  • Double Row Racks

No more than 12 feet deep with a minimum aisle width of 3.5 feet.

  • Multiple Row Racks

Greater than 12 feet deep or are single and double row racks with aisle spaces less than 3.5 feet wide.

  • Shelf Storage

Up to 2.5 feet deep with shelves usually 2 feet apart vertically; separated by approximately 2.5-foot-wide aisles.

  • Bin Box

Five-sided wood, metal, cardboard or plastic boxes with the open face on the aisle. Bin box storage arrays create unique fire control challenges, collecting the water from sprinklers and preventing even distribution down through the racks.

Storage Height

The height in which your material is allowed to be stored presents a unique host of circumstances in the evaluation of fire control. As storage height increases, a sprinkler system must be designed to accommodate the increased fire potential associated with it. Because a fire spreads faster vertically than horizontally, a greater force of water from the sprinklers is necessary to reach the base of the fire. If the storage height exceeds the system’s design criteria, in-rack sprinklers may be necessary to control the fire. In this instance, another option to consider is an early-suppression fast-response (ESFR) system. It will typically allow an increase in storage height for some commodities without requiring in-rack sprinklers.

Clearances and Obstructions

It is important to understand that when designing for proper fire protection of stored products, fire sprinklers must adhere to proper clearances and remain free from any obstructions that could impede the flow of water. Too little or even too much clearance can affect the water’s ability to penetrate to the base of the fire, reducing its ability to slow fire growth. Additionally, fire sprinkler system designs assume for a storage area to remain clear and unobstructed in the aisles. Storage in the aisles could allow a fire to spread horizontally across an aisle to an adjacent rack system putting more demand on the fire suppression system. Therefore, aisles must be kept free of storage to maintain the integrity of the fire sprinkler system designed.

Remember that when making any modifications to your facility’s commodity class, storage height and storage array, this could severely impact your fire sprinkler systems effectiveness in controlling a fire.  Please be sure to consult with your local fire prevention experts before making these changes to receive an analysis of the impact. 

For other valuable information related to occupancies and storage:

SprinklerAge: https://sprinklerage.com/protecting-storage-occupancies/

NFPA: https://www.nfpa.org/News-and-Research/Publications-and-media/Blogs-Landing-Page/NFPA-Today/Blog-Posts/2021/05/07/Occupancy-Classifications-and-Model-Codes

Source: https://www.ryanfp.com/fire-protection-storage-occupancies/