How do Clean Agent Systems Extinguish Fires?
Article Written by: Steve Nelson, Jr.
Purpose
The purpose of this article is to provide a basic understanding of clean agents and how they extinguish a fire.
Introduction
Have you ever wondered what the best method to extinguish a computer fire would be? I dare say that many would agree that water is not the preferred medium to use in this case. Would you begin to fan your computer with your hands, hoping to blow the fire out? Again, this would not be the best solution. What if you had to put out a fire that contained an entire room full of computers? There are solutions that can suppress and extinguish fires without harm to electronics. These solutions are clean agents.
Clean agent systems have been used in the suppression and extinguishment of computer equipment, as well other items, where water is not the best medium to use.
These systems would not be effective if it were not for the early warning detection systems that actuate them. Decreasing the spacing between smoke detectors or the installation of an aspirating smoke detector are ways in which a clean agent system can detect a fire in its earliest stages.
Clean agent systems are currently broken down into two major groups; Halocarbons and Inert gases. Each type has its own characteristics which ultimately drive the decision as to which one should be used in a given situation.
The History of Clean Agents
An agent by the name of “halon” arrived on the scene in the early 1900s (DiNenno and Taylor, 2008). According to DiNenno and Taylor (2008), halon later became known as Halon 1301, which became the preferred agent for computer room protection in the 1960’s. This agent was very effective in the extinguishment of fires and did not leave a residue on equipment when it discharged (Harrington, 2016).
Although effective, Halon 1301 was found to be harmful the for environment. Specifically, Halon 1301 contains Bromine which is known to damage the stratosphere. On September 16, 1987, the United States and 23 other nations signed the Montreal Protocol on Substances That Deplete Stratospheric Ozone which phased out the production of Halon 1301 according to DiNenno and Taylor (2008). The production of Halon 1301 was to be phased out by December 31, 1993. With the phasing out of Halon 1301, manufacturers began to scramble in order to create fire suppression agents which would be effective in extinguishing fires and not harmful to the environment (DiNenno and Taylor, 2008).
The EPA began a new measure in 1994 to ensure that the Halon alternatives were meeting standards which proved they were not harmful to the environment, which was known as the Significant New Alternatives Policy or SNAP (Harrington, 2016). Hence, all of the new halon alternatives were known as clean agents. The standard which governs clean agents is known as NFPA 2001, Standard on Clean Agent Fire Extinguishing Systems. According to DiNenno and Taylor (2008), this standard was first published in 1994.
Clean Agents Defined
According to NFPA 2001, Standard on Clean Agent Fire Extinguishing Systems (2015), clean agents are defined in chapter 3 section 3.6 as an “electrically nonconducting, volatile, or gaseous fire extinguishant that does not leave a residue upon evaporation”. Due to their nature, clean agents are especially effective for protection of data centers. Other applications are areas such as museum vaults, electronic media storage, precious document storage (the Declaration of Independence), and telecommunication centers (Harrington, 2008).
Actuation
A clean agent system in and of itself is simply a large container full of liquid and/or gas. In order to effectively extinguish fires, the clean agent system must be actuated by some means. The primary means by which a clean agent system is actuated is automatically through a suppression control panel. In many of today’s applications, photoelectric smoke detectors are used to detect smoke. According to the Fire Suppression Systems Association training program (2016), photoelectric detectors work “when visible smoke passes through the chamber, light is reflected off the smoke particles onto the photo-voltaic cell causing a signal to be generated.” This signal is relayed from the detector to a suppression control panel.
In order to verify that an actual event is taking place, photoelectric detectors are often programmed into what are called, “cross-zones” and “count-zones”. In a cross-zone, two detectors in separate zones are required to actuate the clean agent system. In a count-zone system, any number of detectors (more than one) can actuate the system. This configuration lessens the chances of a false alarm, and increases the likelihood that an actual fire has taken place.
Another effective means of detection is the aspirating smoke detector. The aspirating smoke detector uses a pipe network installed throughout the area along with an internal fan which continuously samples the air within the area to be protected. The unit uses light sources to identify particles as they go through a chamber. This type of detector can provide a very early warning of smoke, many times while a fire is in its earliest stages. The aspirating smoke detector is also connected to a fire suppression panel.
The aspirating smoke detector can send multiple warning levels and can then actuate the clean agent system once the smoke concentration has reached a predetermined level.
Clean Agents
As mentioned before, there are two main groups of clean agents; halocarbons and inert gases.
Halocarbons
Hydrofluorocarbons
- HFC-227ea (FM-200)
- HFC-125 (FE-25)
- HFC-23 (FE-13)
Fluoroketones
- FK-5-1-12 (Novec 1230)
(NFPA 2001, 2015)
Halocarbons agents are beneficial in that they do not require a lot of storage space, work at low pressures, and do not require a large amount of venting during discharge. Venting is required when the room can be over or under pressurized, so that the remaining pressure can have a means of being released.
These agents require that a room be well sealed. This is required so that the agent can disperse into the room and does not escape through openings within the room. The agent must remain in the room long enough to ensure that the fire does not re-flash and to provide adequate time for emergency forces to respond. Venting may be required for halocarbons. It is necessary that a calculation be performed to determine the size of the vent.
It is best to exit the area immediately upon discharge. A common misconception of these types of systems is that they deplete all of the oxygen out of the room. This is not true. The means by which halocarbons extinguish a fire will be discussed later.
Inert Gases
- IG-55 (Argonite)
- IG-541 (Inergen)
- IG-100 (Nitrogen)
- IG-01 (Argon)
(NFPA 2001, 2015)
Inert gases are stored in Department of Transportation approved cylinders at pressures as high as 4400 psi. The pressure is reduced at either a restriction plate installed in the pipe network or though “flow-control” valves installed on the cylinders. This allows the pressure to be reduced to approximately 600 psi before it enters the room. Inert gas systems typically require more room for cylinder storage than halocarbon systems. The piping requirements for the discharge piping may also warrant thicker pipe due to higher pressures. Inert gas systems require that a vent be installed to relieve the pressure which is created by a system discharge.
Extinguishment
Fire extinguishment is accomplished by removing one of the components which allows fires to exist and continue to grow. A clearer understanding can be made through looking at the fire tetrahedron as shown in Figure 1.
Figure 1. Fire Tetrahedron.
Halon 1301 Extinguishment Method
Halon 1301’s method of extinguishment is to interrupt the chemical reaction of the fire (Jensen and Hughes, 2016). Halon 1301 is released into an enclosure by total flooding. Total flooding is defined in NFPA 2001 (2015) as, “The act and manner of discharging an agent for the purpose of achieving a specified minimum agent concentration throughout a hazard volume.”
This means that a predetermined amount of agent is to be released into the enclosure to achieve a concentration through which a fire can be extinguished in that particular volume.
All clean agents which are being discussed are designed as total flooding systems.
Halocarbon Extinguishment Method
The main method which current halocarbons such as HFC-227ea, HFC-125, and FK-5-1-12 extinguish fires is through heat absorption. The agents have high heat capacities and if the “heat” side of the fire tetrahedron is removed, the fire can no longer exist (Jensen and Hughes, 2016).
Inert Gas Extinguishment Method
The main method by which inert gases extinguish fires is through oxygen displacement. The system will be designed to discharge a given concentration into an enclosure in order to lower the oxygen concentration level to approximately 15% which will extinguish the fire. This particular oxygen concentration level can sustain human life. Higher gas concentrations levels can be achieved but are not safe for human exposure (Jensen and Hughes, 2016).
Conclusion
Halocarbons and Inert gases can be used to effectively extinguish a fire without leaving a residue or interrupting operations. These gases are especially effective for special applications such as computer rooms, museums, and telecommunication centers, to name a few.
The Significant New Alternatives Policy paved the way for new effective fire extinguishing halocarbons and inert gases to be introduced and to phase out the use of Halon 1301 which was found to harm the environment.
Although clean agents can suppress and extinguish a fire, the correct alarm and detection method must be used in order to detect a fire in its earliest stages so the clean agent system can extinguish it and keep it extinguished until fire department personnel can arrive.
There are multiple halocarbons and inert gases currently on the market. Current halocarbons extinguish fires through heat absorption while inert gases lower the oxygen concentration level in an enclosure.
Contact International Fire Protection
At International Fire Protection, we can design and install clean agent fire suppression systems for a variety of facilities. We work with industrial and commercial applications in the Southeastern United States. If you are interested in learning more about clean agents, or if you would like to have a system installed, contact IFP today.
References
- Basic Extinguishing Agents 2 [Slideshow presentation]. Retrieved from:
http://go.flextraining.com/FLC8966/ClassHome.aspx?ClassNumber=18.
- DiNenno, P.J., & Taylor, G.M. (2008). Fire protection handbook (20th ed., Vol. 1). Quincy, MA:
National Fire Protection Association.
- Fike Corporation [Pictures]. (2016). Retrieved with permission from:
http://portal.fike.com/newgraphindex.php?hpg=0.
- Harrington, J.L. (2016). Developments since halon 1301. Fire Protection Engineering, 71, 22-32.
- Introduction to clean agents [Slideshow presentation]. Retrieved from:
https://www.jensenhughesacademy.com/core/course32.php?id=118&eid=30438&review=true.
- NFPA 2001: Standard on clean agent fire extinguishing systems (2015 ed.) (2014). Quincy, MA: National Fire Protection Association.
