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.
Unique Challenges
- Multiple factors combine to create a high fire hazard in warehouses.
- Packaging materials, the goods stored are often highly flammable. Plus, the dense packing and high stacking of items can block water flow in a situation where high ceilings already make it harder to deliver water. Together, the features of storage occupancies create a very challenging situation.
Let’s Understand the Terminologies First !!!
Available Height for Storage
Max. Height at which commodities can be stored above the floor and still maintain necessary clearance from structural members and the required clearance below sprinklers
Encapsulation
A method of packaging that either
consists of a plastic sheet completely enclosing the sides and top of a pallet load containing a combustible commodity, a combustible package, or a group of combustible commodities or
combustible packages, or consists of combustible commodities individually wrapped in plastic sheeting and stored exposed in a pallet load.
Expanded Plastics ( Foamed or Cellular)
Those plastics, the density of which is reduced by the presence of numerous small cavities (cells), interconnecting or dispersed throughout their mass.
Unexpanded Plastics
Unexpanded plastics are higher density materials that may be formed into different shapes such as drums, containers, toys etc.
Free-Flowing Plastic Materials
Those plastics that fall out of their containers during a fire, fill flue spaces, and create a smothering effect on the fire.
High-Piled Storage
Solid-piled, palletised, rack storage, bin box, and shelf storage in excess of 12 ft. (3.7 m) in height.
Reinforced plastic pallet(RPP)
A plastic pallet incorporating a secondary reinforcing material (such
as steel or fibreglass) within the pallet.
Types of Storage Arrangements
Bin Box Storage
Storage in five-sided wood, metal, or cardboard boxes with open face on the aisles in which boxes are self-supporting or supported by a structure so designed that little or no horizontal or vertical space exists around boxes.
Pilletized Storage
Storage of commodities on pallets or other storage aids that form horizontal spaces between tiers of storage.
Solid Pile Storage
Storage of commodities stacked on each other.
Shelf Storage
Storage on structures up to and including 30 in. (0.76 m) deep and separated by aisles at least 30 in. (0.76 m) wide.
Back to Back Shelf Storage
Two solid or perforated shelves up to 30 in. (0.76 m) in depth each, not exceeding a total depth of 60 in. (1.52 m), separated by a
longitudinal vertical barrier such as plywood, particleboard, sheet metal, or equivalent, with a maximum 0.25 in. (6.4 mm) diameter penetrations and no longitudinal flue space and a maximum storage height of 15 ft (4.57 m).
Rack Storage
The horizontal dimension between the face of the loads in racks under
consideration.
According to Survey
Fires in storage properties, . . . account for
I. 15.5 percent of nonresidential structure fires,
II. 19.5 percent of associated property damage,
III. 11.4 percent of associated civilian deaths, and
IV. 9.2 percent of associated civilian injuries.
V. In storage properties, the leading occupancies in which these fires occur are agriculture products storage facilities (38%), unclassified storage facilities (23%), and general-item storage facilities (14%)
Design Checklist for Sprinkler System
- Commodity Class
- Type of Pallet
- Storage Arrangement
- Ceiling height, Storage Height, Ceiling Clerance
- If the Storage is miscellaneous ?
- Other Consideration
Commodity Classification
| Class Or Group | Class or Group Materials |
| Class 1 | Essentially non-combustible products in corrugated cartons on combustible pallets |
| Class 2 | Class I products in slatted wooden crates, solid wooden boxes or multiple thickness paperboard cartons with or without pallets |
| Class 3 | Wood, paper, natural fiber cloth or Group C plastics with or without pallets. May contain a limited amount (5% by weight or volume or less) of Group A or Group B plastics |
| Class 4 | Class I, II or III commodities in corrugated cartons with appreciable amounts (5-15% by weight, or 5-25% by volume) of Group A plastics |
| Plastics | Cartoned Unexpanded Group A Plastic Exposed Unexpanded Group A Plastic Cartoned Expanded Group A Plastic Exposed Expanded Group A Plastic |
Commodity Classification
Design Height can be determined by
(1) What the warehouse manager says the storage height will be limited to
(2) The elevation of the bottom of the lowest beam or structural roof member of the building. This is also refer to by those in the commercial real estate business as the building’s “clear height”
(3) The elevation of the bottom of the lowest steel bar-joist web inside the building
(4) 18” below the deflector of the sprinkler-heads
Sprinkler Selection
A precise design approach is necessary to meet the challenges of these occupancies, an effort that includes using storage fire sprinklers.
Limits of Ceiling Only Sprinkler
Table illustrates how the efficiency of ceiling-only sprinkler protection decreases with ceiling height above 30 ft. Increasing the ceiling height by just 5 ft., 17%, from 30 ft. to 35 ft. increases the basic sprinkler water demand by more than 50%. Increasing the ceiling height by 60%, from 30 ft. to 48 ft., increases the basic sprinkler water demand by 140%. Thus, even in buildings that could be protected with ceiling sprinklers, ceiling-only sprinkler protection may not be the most efficient use of water.
- The discussion so far has referenced protection criteria for Cartoned Unexpanded Group A plastics. More hazardous commodities such as tires, Exposed Group A plastics, and aerosols present an increased challenge to a sprinkler system.
- These commodities typically require in-rack sprinklers to be provided at lower storage heights than would be required for a Cartoned Unexpanded Group A plastic commodity.
- For example, NFPA 13 limits storage of rubber tires on racks to 35 ft. of storage under a 40 ft. ceiling with ESFR sprinkler protection at the ceiling. The criterion requires more than 2,600 gpm of basic sprinkler water demand from K25.2 ESFR sprinklers.
- Thus, while ceiling-only criteria are available for storage of Cartoned Unexpanded Group A plastics under ceilings up to 48 ft. tall, other commodities have lower ceiling height limits for ceiling-only protection. Even when ceiling-only protection options are available, the water demand or other required features may make the installation of in-rack
sprinklers preferable.
Ceiling-Level Sprinkler System Design Criteria
The design guidelines for ceiling-level Storage sprinklers are based on five main attributes assigned to a sprinkler. They are:
1) K-Factor (orifice size)
2) Orientation (pendent or upright)
3) Response time index rating (quick-response or standard-response)
4) Nominal temperature rating
5) Sprinkler spacing (standard or extended-coverage)
Once the commodity hazard, storage arrangement, and peak ceiling height for the protected area is known, the protection design options for the sprinkler system can be determined using the appropriate protection table in combination with the five sprinkler attributes
Example
- Type of Commodity : Class 4, Encapsulated
- Storage Height : 18 feet
- Building Height : 23 feet
- Type of Rack Arrangement : Multiple row Rack with Aisle 15 feet deep
- Aisle Width : 6 feet
- Type of Sprinkler System : Wet Type
Determine Requirement of in rack sprinklers
