Clean agent fire suppression for mission critical facilities

Clean agent systems have changed over the years due to a variety of reasons, including safety and product updates. Know the design parameters and codes and standards that dictate the specification of clean agent systems.

05/22/2017


This article is peer-reviewed.Learning objectives:

  • Know the codes and standards that guide fire protection engineers when selecting clean agent fire suppression systems.
  • Understand the reasons clean agent systems might be specified in a building.
  • Learn which mission critical facilities require clean agent fire suppression systems.

In the 30 years since the signing of the Montreal Protocol of 1987 ended the viability of halon 1301 as a fire suppression agent, a concerted effort to develop a replacement clean suppression agent has been underway. The struggle to develop a halon alternative led multiple chemical corporations, such as 3M and DuPont, in many different directions, leaving the codes and standards field to develop guidelines for the use of these newly developed agents.

NFPA 2001: Standard on Clean Agent Fire Extinguishing Systems was first released in 1994 as a response to industry and governmental calls for clean agent selection, usage, and installation guidelines. Rather than develop a standard for each separate type of agent in development, NFPA authored the standard in such a way that it would apply to all clean agents. NFPA 2001 identifies clean agents as “electrically nonconducting, volatile, or gaseous fire extinguishants that do not leave a residue upon evaporation.”

These properties make clean agents especially useful for fire protection of data centers and other mission critical facilities, along with archive-storage and other special-purpose facilities in which water-based fire protection systems could damage room contents or cause major business disruption.

Table 1: Some common clean agents and their chemical makeups. All graphics courtesy: Koffel AssociatesWhile clean agents can be used in local-application scenarios, the vast majority of clean agent systems are total-flooding systems. In a total-flooding system, the agent is dispersed throughout the entire volume of the space being protected to ensure that a minimum agent concentration is achieved throughout that volume, thus extinguishing the flame. Popular from the 1960s until the halt of their production in 1994, halons are extremely efficient at extinguishing fire and relatively cost-effective to produce and employ. However, they have been shown to negatively impact the environment. Thus, the environmental impacts of replacement agents are a primary concern and are measured using three objective criteria:

  • Global warming potential
  • Ozone-depletion potential
  • Atmospheric lifetime.

Due to legislative measures driven largely by these environmental concerns, perfluorocarbons and hydrochlorofluorocarbons are being rapidly phased out of use, leaving halocarbon compounds and inert gases as the current clean agent types of choice. Looking beyond environmental impacts, new clean agents also are judged based on toxicity, their decomposition when released in a fire environment, and extinguishment effectiveness per mass, as well as cost-effectiveness and marketing capabilities. From a safety perspective, any agent included in NFPA 2001 has been evaluated in a manner equivalent to the process used by the U.S. Environmental Protection Agency’s Significant New Alternatives Policy (SNAP) program for total-flooding agents.

As previously noted, halocarbon compounds and inert gases make up the majority of the current total-flooding clean agent market. While they both adhere to the general definition of a clean agent, they achieve flame extinguishment in different ways and have unique benefits and disadvantages. Halocarbons extinguish flames by reducing flame temperature to the point that a flame can no longer be sustained. Common halocarbons include hydrofluorocarbons, such as HFC-125 and HFC-227ea, and perfluoroketones, such as FK-5-1-12. Inert gases and combinations thereof extinguish flames by reducing the ambient air temperature and/or decreasing the oxygen level in the hazard volume below minimum levels required to sustain a flame. Some popular inert gas clean agents include IG-01, IG-55, and IG-541 (see Table 1). Though outside the scope of NFPA 2001, carbon dioxide systems can sometimes be an option in mission critical facilities.

Figure 1: This close-up is of a two-tank FK-5-1-12 manifold system installed in a small data center room. Only one cylinder is active at a time. Note the keyed switch to manually change the active cylinder (in green in the photograph). How to select a clean agent

With the numerous clean agent options available to the consulting engineer, it is prudent to consider a number of different factors when specifying a clean agent for a mission critical facility. One of the most important factors is cost. Most available clean agents and their required nozzles are highly proprietary; therefore, finding reliable pricing information is almost always a matter of contacting a sales representative for the agent in question.

In addition, the quantity of agent required to achieve the desired concentration will differ between agents, such that a price-per-pound analysis is not always a useful comparison. Again, contacting a sales representative is typically the best way to get an accurate estimated cost.

Additional considerations include:

  • The type of hazard being protected
  • Local availability of the agent
  • Available space for agent cylinders
  • Presence of an existing halon system.

Some clean agents are designed with the intent to extinguish deep-seated Class C fires (i.e., electrical), such as those in a server rack, while other agents have been developed to protect Class A fires consuming solid fuels (i.e., paper and plastic). Testing has shown that the discharge of some clean agent systems can have a negative effect on the performance of hard disk drives in data center applications. The probability of hard drive problems is higher in some situations than others, but as a general rule, halocarbon systems tend to cause less interference with disk drives than inert gas systems. If hard drive performance is a primary concern in the facility being protected, further analysis to determine the risks involved may be required.

Availability of the desired clean agent can be a major selection factor in remote locations, such as mission critical facilities on military bases or in climates with extreme weather or security-related access concerns. The ability to replenish agent supplies can also become a major concern if the space is expected to be subject to regular discharges or if regulations prevent a facility from continuing operations until the clean agent suppression system is recharged and active.


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