By Lyth B. Clark, Jr., P.E., CFEI
Sprinkler systems are very effective for reducing losses of life and property in building fires. A good sprinkler system does not just happen. In designing a sprinkler system, the determination of the hazard classification to be protected is a critical element. The hazard classifications found in National Fire Protection Association (NFPA) 13 include light hazard occupancy, ordinary hazard occupancy, and extra hazard occupancy. These definitions evaluate the contents of the building, or the fire load, and how they are used, trying to gage the possible rate of fire spread.
Not all buildings and contents are created equal.
Case Study I:
An owner asked for a sprinkler needs assessment from a Fire Protection Engineer. The building contained a plastic furniture manufacturing operation with the storage of raw materials on one end, manufacturing in the center, and the storage of finished product on the other end. The sprinkler standards referenced, NFPA 13 - Installation of Sprinkler Systems, NFPA 231C - Rack Storage of Materials, and NFPA 231 - General Storage, were guidelines that were correctly used in designing a sprinkler system for this facility. In determining the sprinkler system design, the following must be considered: type of material to be protected, height and manner of storage of the materials, and the fire risk and hazards of the operation. The Fire Protection Engineer provided the owner with minimum design criteria for water density and area coverage for the three areas. The owner was not required to satisfy the highest design criteria throughout the building but only in the corresponding high hazard area. Sprinkler contractors were provided with the criteria for bidding. Because of the complexities involved in completing retrofit jobs of this nature, only one sprinkler contractor submitted a bid. The owner, comparing the design criteria proposed by the contractor and the criteria supplied by the Fire Protection Engineer, noted that the contractor did not classify the high piled and rack storage areas as NFPA 231 and 231C systems. Neither was the plastics manufacturing processes located in the building center classified as an extra hazard occupancy. The contractor's proposal was to install an ordinary hazard system throughout. This system would not have met code.
Would it have worked? Yes, but not well enough in a serious fire. The owner was not satisfied with this proposal because of the knowledge he had gained from the Fire Protection Engineer's assessment and therefore, put the project out for bid again. This time several contractors bid on the project and a complete set of drawings were provided by a fire protection engineer. The job was completed and a special application sprinkler head was used that provided the same density and area of flow throughout the building. The owner received a system that allowed him flexibility for his operation, ease of maintenance in that different sprinkler heads would not have to be provided for replacements, and economy in the overall design, both of the water required and the pipe sizes needed.
Would an owner unaware of his needs have accepted the earlier submittal by the lone contractor? Yes, and the project would have gone forward through the subsequent design and installation phases. Would the Authority Having Jurisdiction (AHJ), which could have been a state, city or county official, have approved the sprinkler system? Probably yes, because the AHJ is not required to be on the site before or after the installation. The limitations of this system would only become apparent to the responding fire department in the event of a fire or to fire cause investigators after the building has burned down.
Case Study II:
The sprinkler contractor is called out to the facility and escorted by the owner's representatives through the new areas that the building code requires to be sprinklered. The plans are submitted to the Authority Having Jurisdiction who decided to send a Reviewing Plans Examiner to inspect the facility. During the inspection, the plans examiner discovered that the majority of products stored in racks in the new areas are encapsulated, enclosed by a plastic sheet on the sides and over the top of the pallets of goods. The sprinkler contractor had noted non-encapsulated storage. When the contractor was asked about the storage, he stated that he had seen none during his preliminary inspection. When asked what areas he had toured, it became apparent that the sprinkler contractor was "guided" on his tour and did not observe the complete operation. Encapsulated storage requires more water to fight the fire. The plastic covering hinders water from reaching the fire inside individual pallets and from pre-wetting nearby pallets. Any plastic covering on top of a pallet load covering more than fifty percent is considered encapsulated by definition. Regardless of the number of encapsulated pallets, any encapsulation would require a system with a higher water density. The packaging of these products in this way increased the risks and hazards. The contract between the owner and the sprinkler contractor stated that the sprinkler contractor would design a system that met NFPA 13 code. Therefore, the higher density sprinkler system was ultimately installed with the sprinkler contractor absorbing the cost even though the owner may not have been completely forthcoming with the information needed to properly assess the design needs.
The determination of the hazard is not always straightforward, but should be. It is also important to note that hazards can change. A sprinkler system installed when the building occupancy was that of a beverage manufacturer might now contain a solvent cleaning and open oil quenching operation. High roofs may invite storage to creep ever upward increasing the fire loading. As discussed in NFPA 921, Fire Protection Engineers understand the relationship between ignition sources, fire dynamics, fire detection and suppression systems (how they work and fail) and are knowledgeable of building and fire codes, fire test methods, fire performance of materials and failure analysis. Fire Protection Engineers design fire protection systems accordingly.
A simple but valid question to ask when approaching the site of a burned building with sprinkler pipe sticking up through the rubble is "Why did the system fail?" Fire Protection Engineers at The Warren Group have experience in analyzing failed systems and are happy to assist you with fire protection and prevention matters.
Examples of Hazard Classification as noted in Fire Protection Handbook, 8th edition
Light Hazard:
Office Buildings
Schools
Residential occupancies
Public assembly
Ordinary Hazard
Canneries (Group 1)
Electronic plants (Group 1)
Restaurant service areas (Group 1)
Dry cleaners (Group 2)
Libraries (Group 2)
Repair garages (Group 2)
Wood product assembly (Group 2)
Extra Hazard
Combustible fluid use area (Group 1)
Printing (inks with a flash point below 100 F (Group 1)
Upholstering with plastic forms (Group 1)
Flammable liquids spraying (Group 2)
Manufactured home assembly (Group 2)
Plastics Processing (Group 2)
Beyond this basic group, special circumstances must be considered for buildings that contain substantially larger quantities of materials than what is contemplated by these descriptions.
Source: Fire Protection Handbook, 8th edition