Selecting a fire protection system
System design, installation standards
Virtually no comprehensive guidance facilitating the decision as to why one type of system should be chosen over another is available as a regulatory document or generic application guide. Instead, each reference standard tends to provide some commentary about the fire hazards that could be protected against using the given system addressed by the standard. Depending on the specific reference standard and system, certain design and installation provisions could also be provided. For instance, NFPA 12: Standard on Carbon Dioxide Extinguishing Systems includes information about the design of the carbon dioxide systems for a specific hazard once a decision has been made to install a carbon dioxide system for that hazard. Such information can include design concentrations, flooding factors, and volume factors specific to these types of systems.
Some standards relay system application information in other forms. NFPA 2001 provides advisory annex language indicating that clean agent fire extinguishing systems are useful within certain limits for extinguishing fires in specific hazards or equipment, and in occupancies where an electrically nonconductive medium is essential or desirable or where cleanup of other media presents a problem. Such total flooding clean agent systems are used primarily to protect hazards that are enclosed or equipment that in itself includes an enclosure to contain the agent. A list of typical hazards that could be suitable for protection by clean agent systems is provided and includes:
- Electrical and electronic hazards
- Subfloors and other concealed spaces
- Flammable and combustible liquids and gases
- High-value assets
- Telecommunications facilities.
NFPA 2001 also states that clean agent systems could be used for explosion prevention and suppression where flammable materials collect in confined areas.
Other reference standards do not directly identify the hazards they are intended to protect, but rather tie the appropriateness of the system to specific listing and testing requirements. For example, NFPA 750: Standard on Water Mist Fire Protection Systems states that water mist protection systems are to be designed and installed for the specific hazards and protection objectives specified in the listing. The characteristics of the specific application, such as compartment variables and hazard classification, are to be consistent with the listing of the system. Furthermore, an evaluation of the compartment geometry, fire hazard, and system variables must be performed to ensure that the system design and installation are consistent with the system listing.
In turn, NFPA 750 requires the listing of water mist fire protection systems to be based on a comprehensive evaluation designed to include fire test protocols, system components, and the contents of the manufacturer's design and installation manual. An annex in NFPA 750 includes a list of fire test protocols and the associated listing organizations. It should be obvious that the consulting design engineer needs to be sufficiently familiar with the application and limits of the listing protocols, as well as the design and installation manual for each type of water mist system that might be under consideration.
It is important to recognize that with many of these “alternative” or “other” systems, not just water mist systems, a generic design approach, such as for automatic sprinkler systems as outlined in NFPA 13: Standard for the Installation of Sprinkler Systems, does not exist. Many of these “alternative” systems are of a proprietary nature and the design and installation provisions are specific to the manufacturer of each type of system. For a given hazard, the design, installation, and operational details of one manufacturer’s water mist system are likely to be significantly different from that of another manufacturer. It is worth noting that even with sprinkler systems, more specialized devices are entering the marketplace.