For over half a century from 1910 to the late 1960s, when a clean,
dry, gaseous fire-extinguishing agent was required, carbon dioxide was
the choice, usually the only available choice. In the late 1960s, the
"halons" became commercially viable alternatives to carbon dioxide for
applications where the life safety risks posed by carbon dioxide were
considered unacceptable. In particular, halon 1301 became popular as a
fire protection agent for total flooding spaces where personnel might be
For nearly two decades, halon 1301 was the gaseous agent of choice
for protection of areas containing high-value electronic equipment.
Halon 1301 also made inroads to the marine fire protection market for
total flooding machinery spaces where flammable liquids presented the
primary risk. Halon 1301 was also widely used in aerospace and military
By the mid-1980s, a growing body of scientific data indicated that
halons were contributing to depletion of the stratospheric ozone layer.
In 1987, the Montreal Protocol was adopted requiring a phase-out of
halon 1301 production in developed countries. The U.S. Clean Air Act
Amendments of 1990 banned new production and import of halons into the
United Stated as of 1994. These regulatory actions triggered an
accelerated search for gaseous fire extinguishing agents to replace the
popular halon 1301. In the U.S., existing halon systems are still
permitted and the use of recycled halon is allowed. However, in recent
years, new installations have become very rare.
Next year marks the 20th anniversary of the Montreal
Protocol. During the last two decades, a number of gases have gained
acceptance as halon replacements --- "life-safe" alternatives to
traditional carbon dioxide fire protection for total flooding
applications. NFPA 20011 covers the use of "halon alternatives." The current Standard 2001 lists over a dozen "halon alternatives."
Some of the halocarbon agents currently included in NFPA 2001 are
HFC227ea (FM-200™, FE-227™), HFC-125 (FE-25™), HFC-23 (FE-13™), and
FK-5-1-12 (Novec 1230™) as well as a number of "blends," that is,
combinations of various chemical agents. The inert gases identified in NFPA 2001 are
nitrogen (IG-100) and argon (IG-01) and mixtures of 50 percent nitrogen
and 50 percent argon (IG-55). There is also a mixture of nitrogen and
argon with a small amount of carbon dioxide (IG-541, trade name
Choosing a Gaseous Agent
If the fire protection engineer determines that a space would best be
protected by total flooding with a gaseous agent, the choice of the
many available agents should be given careful consideration. The
engineer may consider whether traditional carbon dioxide protection is a
desirable or viable option. If people will normally be present in a
space, carbon dioxide should generally be eliminated as an option.
(There may exist specialized applications where people are normally
present that are best protected by total flooding carbon dioxide. NFPA 122 covers the considerations for such hazards.)
When a clean agent is required, halocarbon and inert gas clean agents each have advantages and disadvantages.
"Clean Agent" Considerations
When floor space for the agent storage is limited, halocarbon clean
agents often have an advantage. If the clean agent storage must be
located some distance from a protected space, inert gases may sometimes
have an advantage. When flammable liquid hazards are to be protected
with a clean agent, availability of data for inerting concentrations
using the agent/fuel combination must be considered. Availability of
listings or approvals for specific hazards, such as Marine hazards, can
affect the choice of agent. Other considerations may include cost, local
availability of the agent for recharge, and operating temperature
Jurisdictions within the United States generally accept agents that are included in NFPA 2001.
If the system is to be installed outside the United States, the
engineer should check local regulations for possible restrictions on the
use of the agent of choice.
"Class A" and "Class C"
If the fuel is electrical equipment, such as computer or telecommunications equipment, virtually all of the clean agents in NFPA 2001 are
listed and approved for such hazards when electric power to the
equipment is shut down upon discharge of the clean agent. All clean
agents listed by UL or approved by FM per NFPA 2001 guidelines
have been tested to determine their "Class A" fire-extinguishing
concentrations. The "Class A" fire tests include not only the
traditional "wood crib" fire but also arrays of plastic materials
simulating the fuels in computer and telecommunications equipment.
Although the "Class A" fire tests use fuels simulating those found in
electrical equipment, they are not representative of fire scenarios
where electrical energy is continuously supplied to the fuel array.
Limited testing with clean agents on fuel arrays where electrical power
is maintained after application of the clean agent indicates that higher
concentrations of clean agent than the "Class A" concentrations may be
needed to extinguish the fire. As of this writing, the NFPA 2001 technical
committee continues to study this issue. Electric power to the
protected equipment should be shut down upon discharge of a clean agent
unless issues related to possible reflash and continued agent
decomposition (in the case of halocarbons) are adequately addressed.
Presently, the designer should seek advice from the system manufacturer
for such hazards where electrical power shutdown has untenable
If the space to be protected contains quantities of flammable liquids
and gases, the engineer must select an agent for which the
flame-extinguishing and possibly the inerting concentrations for the
specific flammable fuels have been determined. Alternatively, the
engineer could arrange for determination of the required concentration
by laboratory testing.
A notable difference between the fire protection using carbon dioxide and the "clean agent" alternatives to CO2 is the consideration of inerting versus flame-extinguishing. All total-flood carbon dioxide systems designed with CO2 concentrations per NFPA 12 produce
an "inert" atmosphere --- precluding fire or explosion of even
stochiometric mixtures of fuel and air with a persistent ignition source
for as long as the specified CO2 concentration remains.
NFPA 2001 recognizes two levels of protection for flammable liquids and gases --- flame-extinguishment and inerting. NFPA 2001 requires
inerting concentrations to be used for hazards involving Class B fuels
if "conditions for subsequent reflash or explosion could exist." 1 Annex A of NFPA 2001 describes such "conditions."
Practically speaking, nearly all hazards where flammable liquids are
the primary fuel load would best be protected by systems employing an
Although many alternatives have been developed, no single alternative
has emerged with all of the desirable characteristics of halon 1301.
There are, however, some fine alternatives that provide excellent fire
protection. "Clean agent" development is now focusing on developing
design criteria for hazards involving electrical equipment where
equipment cannot be de-energized, standardizing the cup burner test used
to determine flame-extinguishing concentrations for Class B fuels,
refining requirements for room pressure venting during clean agent
discharges, and expanding the database of inerting concentrations.
Tom Wysocki is with Guardian Services, Inc.
1NFPA 2001, Clean Agent Fire Extinguishing Systems, National Fire Protection Association, Quincy, MA, 2004. 2NFPA 12, Standard on Carbon Dioxide Extinguishing Systems, National Fire Protection Association, Quincy, MA, 2005.
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