Know when, where to specify a clean agent system
Fire protection engineers should use NPFA 2001 to direct the specification of clean agent fire extinguishing systems, which are typically used in mission critical facilities.
- Compare and contrast clean agent fire extinguishing systems.
- Evaluate their use and outline the codes and standards used to dictate their specification.
- Assess the pros and cons of various clean agent systems.
Clean agent systems were initially developed to address emerging technologies related to the computer, aircraft, and marine industries. Halon 1301, one of the most common clean agents in its time, was developed in the 1960s. Its primary use was to provide fire protection to sensitive equipment related to computer mainframes and telecommunications equipment on aircraft and marine vessels. It was a very efficient means of fire protection that left no residue after discharge, and was a relatively lightweight means of suppression. As technology advanced and environmental concerns became important, the need for alternative agents became evident.
Modern clean agents were developed to replace earlier gaseous-based systems that had been determined to have a detrimental impact to the environment. Halon 1301 and 1211 were found to deplete ozone when exposed to the atmosphere. There was a clear need to provide alternative fire-extinguishing agents that were safer to the environment, or cleaner. Hence clean agents were developed. They are defined as an electrically nonconducting fire extinguishant that does not leave a residue upon evaporation.
In 1989, the Montreal Protocol determined that halon gases, including those used in fire-extinguishing systems, when exposed to the atmosphere caused a depletion of the ozone layer. As such, a ban was placed on the production and continued use or sale of halon-type fire-extinguishing systems. In the United States, the U.S. Environmental Protection Agency banned the manufacture of halon in the mid-1990s. This caused the need to develop alternative extinguishing agents and systems. The Technical Committee on Halon Protection Options was organized in 1991 and started working to address standards for those systems replacing halon. They cited a need to develop standards on how to design, install, maintain, and operate the newer systems being developed.
As a result of the work performed by the committee and the NFPA, NFPA 2001: Standard on Clean Agent Fire Extinguishing Systems was formed. This standard provides minimum requirements for the design, installation, testing, maintenance, and operation for both total flooding and local-application clean agent systems used to protect property and equipment against fire. The standard was first published in 1994 and was developed to address alternatives to halon extinguishing systems.
Since its initial publication in 1994, the standard has been updated multiple times and 2015 is the current edition. The standard has been updated to reflect changing technologies in the manufacture of clean agents, their use, and application in fire-extinguishing systems. The current edition includes new content to address recycling and disposal of the agents and higher-pressure agents.
NFPA standards provide criteria on how to design, install, test, maintain, and operate the systems they govern. They do not dictate when these systems are required, which is typically left to the governing building and/or fire codes. These codes will require a certain level of protection and the NFPA standards will guide those involved in how to design and install the systems. NFPA 2001 addresses the requirements for system components, system design, local application systems, inspection, testing, maintenance, and training as well as requirements for marine systems. Annex material provide additional explanatory material to support the designers, installers and users of these systems. NFPA 2001 is the standard that dictates how to design and install clean agent systems. By reference within a building or fire code, the standard becomes enforceable, as it is part of the governing codes.
Clean agent systems are typically used to protect sensitive electronic equipment or valuable property and equipment against fire. They can be used in conjunction with, or as a replacement for, water-based systems. Because the agent does not leave a residue after application, it can limit the damage caused by other types of extinguishing systems and is easier to return to normal operations because cleanup time is reduced. Clean agent systems are very common in protecting data-processing centers or rooms where computer equipment and servers are present. Clean agent systems can be a valuable tool in protecting sensitive electronic equipment or valuable property and equipment.
Many of the model building and fire codes require automatic sprinkler systems to protect the building based on the use and size of the building. They do permit alternative extinguishing systems in lieu of sprinklers under certain conditions. The International Building Code (IBC) 2012 edition allows alternative systems under Section 904. This section references NFPA 2001 when clean agent systems are to be provided as part of the protection for the building. The use of these systems requires the approval of the fire code official, as they are considered alternative systems in the code. It also should be noted that their use may not allow other exceptions or reductions permitted by code for sprinkler protection. Therefore, the designer must carefully examine the application of the alternative system and make sure it does not impact other design components.
When complete automatic sprinkler protection is required by code, there are certain options that a designer of clean agent systems can use. One includes the application of only a clean agent system for the room to be protected, and a fire-resistance rating around the room to reduce impact to a fire from this room to the remainder of the building. If the room is relatively small with respect to the overall size of the building, this option could be used to protect the space and still obtain reductions and exceptions for the overall building because limited areas of the building are not protected by sprinklers. This approach should be specifically discussed and agreed upon with the fire code official.
The second option is to use a clean agent system in conjunction with a water-based sprinkler system to protect the space. The water-based system gives a code-compliant approach to providing automatic sprinklers for all areas of the building, or a fully sprinklered building. This option should be explored when full automatic sprinkler protection is required and the use of the clean agent system in lieu of sprinklers is not allowed. The clean agent system gives a first line of defense against a fire that, if extinguished, should not actuate the water-based system. If fire growth continues, the water-based system will provide protection of the building.
It is not uncommon for a pre-action sprinkler system to meet the automatic sprinkler system code requirements and then supplement a clean agent system for protection of the equipment. The pre-action system does not have water in the system prior to activation, thus mitigating the potential for water damage. The pre-action system can be designed to require two detection components to operate before the water is released into the room. This can be a combination of smoke detection and sprinkler actuation. If only one actuates, water is not released. The clean agent system can be designed to use the smoke-detection system to release the agent and provide a first line of protection, thereby protecting the equipment or valuable property before the water-based system releases to protect the overall building.
There are many detection arrangements available for clean agent systems. Within areas with sensitive electronic equipment, such as data rooms, often the choice is an aspiration-type detection system. This type of system uses a series of pipes with sampling ports in the protected area that are connected to a detector housing that draws the air from the space through the detector piping network. These detectors can detect minute particles of smoke and can detect fires at the very early stages, often before the fire or smoke is even visible. They provide an extra line of defense for the operators because the presence of a fire can be detected well before the clean agent system is needed and provides alert levels to notify operators.
The design of clean agent systems will be dependent upon the type of system chosen and the criteria set forth in NFPA 2001. For most applications, a total flooding system is chosen where the agent is released into the entire room or enclosure. Local application systems are available; the most common system applications are those designed for total flooding. A total flooding system uses a detection system to detect the fire, such as a smoke-detection system discussed above, which is monitored by a control panel that in turn releases the clean agent into the room when required. The control panel serves as the releasing panel as well. The agent is released into the room or enclosure through a network of piping and nozzles designed to convert the agent into a gas at discharge. This gas will then disperse throughout the room to extinguish a fire. The amount of gas is determined by calculations based on the percent concentration needed to extinguish the fire. This is also dependent upon the type of agent being used.
Storage and dispersal
The clean agent is stored in tanks or cylinders near or adjacent to the area being protected. The clean agent is typically stored under pressure to propel the agent through the piping network. The amount of storage tanks required is dependent upon the type of agent being used. Some agents can use more or less than other agents and this needs to be factored into the design so that adequate storage is provided. Consideration also should be given to the need for installed backup or reserve cylinders connected to the piping network. This allows the room or enclosure to remain protected after discharge without the need to immediately refill the tanks. This can save downtime in restoring operations, but will require extra storage space. Otherwise, before protection can be restored, the tanks would need to be replaced or refilled by the suppression system supplier.
As noted above, the design of the clean agent system will depend partly on which type of agent is used. NFPA 2001 identifies two types of clean agents: clean halocarbon agents and inert gas agents. There are several manufacturers of each; the more common is the clean halocarbon agents that were first developed as replacements to Halon 1301. The goal was to find a drop-in replacement for these systems, but the physical properties of the alternative agents did not allow for this. Clean halocarbon agents will typically contain compounds of one or more of the following elements: fluorine, chlorine, bromine, or iodine. An inert gas agent contains one or more of the following gases: helium, neon, argon, or nitrogen. In general, an inert gas will require higher concentrations to extinguish a fire than a clean halocarbon will. This results in more agent to extinguish the fire and, therefore, more containers to store the agent.
There are many design considerations to any fire protection scheme, including those associated with clean agent systems. Clean halocarbon agents will use less agent and, therefore, have fewer storage requirements. They are more common in the marketplace and can be used for a variety of protection schemes. Inert gases are considered by some as more environmentally friendly than halocarbons but use more agent, requiring more storage cylinders. They also discharge at higher pressures and require relief vents to avoid damage to the room or building. Venting direct to the exterior is ideal, but is not always practical.
Safety and environmental concerns
Inert gases are comprised of gases found in the air we breathe. Some people say this lends to them being less harmful than halocarbon agents. That is not to say halocarbons are not safe, it is just that inert gases comprise gases found in the air, whereas halocarbons are chemical compounds. Inert gases do not have a global warming potential (GWP) impact, whereas halocarbons do. There are some who believe that the GWP impact of clean halocarbon agents will cause them to be banned in the future. However, there do not appear to be any plans to ban the current halocarbons for fire-extinguishing systems because they would have limited impact to the environment due to the amount being used. The EPA currently approves several clean halocarbon agents for fire-extinguishment use.
Modern clean agent systems were developed to allow the continued use of a gaseous-type suppression system while addressing environmental concerns. They are considered clean agents as they do not leave a residue, so they are well-suited to protect sensitive electronic equipment and valuable property. When considering the application of a clean agent fire extinguishing system, NFPA 2001 provides specific guidance on how to design and install them.
Allyn Vaughn is the president of JBA Consulting Engineers. He has been involved in the fire protection industry for more than 30 years, designing fire protection suppression and detection systems on a variety of projects. He designs clean agents systems, including server rooms, data rooms, and other highly sensitive areas.