While the list may get longer as time goes on, end-users who 15 years ago would have
employed halon 1301 systems to protect their facilities or equipment have four clear
options in fire protection systems today:
1. Use an “in-kind” halon 1301 alternative such as a halocarbon, inert gas or
carbon dioxide based system, …..
2. Use a “not-in-kind” alternative like water mist or pre-action water sprinkler
system, …..
3. Use a very early detection system with no specialized fire suppression or …..
4. Do nothing.
Available Fire Protection System Alternatives to Halons in Fixed Systems
Gaseous Extinguishing Agents for Fixed Systems
During the halon era (late 1960’s to late 1980’s), two halons emerged as the market
leaders: halon 1301 for total flooding systems and halon 1211 for use as a streaming
agent in hand portable and hand hose line extinguishers. The decision about what
agent to use where and when was rather straight forward.
Today there is a proliferation of at least 13 different gaseous
agents in various states of commercialization vying for a place in the markets once served by halon 1301. Indeed, there are even more under review at the US EPA for possible addition to the SNAP 16 list.
For a halon alternative to reach commercial acceptance in the US, there are at least 4
steps in the process and until all four are achieved, the agent will see little or no
success. These steps, in the chronological sequence one would likely approach them,
are:
1. Inclusion in the US EPA’s SNAP 19 list as an acceptable alternative where the
focus is primarily on the health and environmental effects of the agent.
2. Inclusion of the agent in a technical standard of the National Fire Protection
Association which is intended to provide guidelines to the users concerning the
design, installation, operation, testing and maintenance of fire protection systems or
extinguishers employing the agent.
3. Component listing or approval of the agent itself by a nationally recognized
testing laboratory such as Underwriters Laboratories or Factory Mutual.
4. Listing or approval by a nationally recognized testing laboratory of a fire
protection system or hand portable extinguisher incorporating the agent.
Water Mist Systems
To many, water is perceived as a tremendous fire extinguishing agent, it’s readily
available, it’s inexpensive and it’s environmentally non-problematical. Further, the
concept of using it in a mist form makes water even more attractive as a fire
extinguishing agent since:
- The high effective surface area of the water mist “particles” makes it more
capable (than a heavy stream of water) in its process of cooling the fuel and the
surroundings and in readily evaporating (turning into steam) and diluting the
oxygen, thus inhibiting the fuel burning rate and …..
- That increased effectiveness then translates into requiring very small quantities
of water to achieve extinguishment (when compared to more conventional water
application methods) thus minimizing the largest single objection to water
systems - the collateral damage done by the water.
Water mist has made in-roads into 3 major market applications: the protection of turbine
and diesel powered machinery, the protection of machinery spaces aboard ships and the
protection of passenger cabins aboard ships. There are accepted test protocols (Factory Mutual Research 20 for the turbines and the International Maritime Organization (IMO) 21, 22, 23 for shipboard) for these market applications and those who have their
systems successfully tested have achieved the right to participate.
While the technology is certainly developing, there are two things that are really holding
water mist back from gaining wide market acceptance:
- First, the water mist fire protection systems have been found to have difficulty extinguishing small fires in
large volumes even to the point that they fail to extinguish those small fires.
- Second, the water mist industry has been unable to effectively bridge the gap
between theory and practice, thus requiring that applications be limited (in size
and characteristics) to those where fire test protocols have been developed
against which system performance has been determined empirically. The
economics of this approach are unattractive to systems’ manufacturers and end
users.
There is a lot of effort on an international scale going into solving these problems and
many researchers are confident that the solutions are well within reach.
Preaction Automatic Fire Protection Sprinkler Systems
A preaction automatic sprinkler system is generally used where there is special concern
for accidental discharge of water as in areas containing essential electronics. A
preaction valve is placed in the water supply piping and a separate detection system,
most often smoke detection, is used to activate the valve to allow water to flow into the
sprinkler piping. The sprinkler piping is much like that found in a conventional system
with closed head sprinklers that do not open until activated by the heat from a fire.
When the system is in a standby mode with the preaction valve closed, the sprinkler
piping downstream of the valve is often pressurized with air and that pressure is
monitored as a continuous supervision of the integrity of the piping.
In the event of smoke detection, the preaction valve will be opened but water will not
flow into the sprinkler piping until a sprinkler head is operated by the heat of a fire.
When the sprinkler head operates, any supervisory air in the system vents through that
open head followed by the water allowed into the piping by the opened preaction valve.
Much of the damage reported over the years caused by water to essential electronic
equipment has been as the result of some form of failure of the wet pipe sprinkler
system, either in the piping itself or some sort of failure of the sprinkler head itself. In the
preaction fire protection system, two separate events consisting of the (1) detection of smoke adequate
to cause the opening of the preaction valve and (2) the development of enough heat to
open a sprinkler head are necessary before any water would be discharged. Thus the
accidental discharge of water from this type of system is highly unlikely.
Other Types of Agents for Fixed Fire Protection Systems
In addition to the gaseous agents listed in Table 14 and the water based systems, there
are several other types of agents being promoted as halon replacements in fixed
systems, including inert gas generators, aerosols and some special halocarbon based
compositions.
Inert Gas Generators
Inert gas generators utilize a solid material which oxidizes rapidly, producing large
quantities of CO2 and/or nitrogen. The use of this technology to date has been limited to
specialized applications such as dry bays on military aircraft. This technology has
demonstrated excellent performance in these applications with space and weight
requirements equivalent to those of halon 1301 and is currently being deployed in the
Navy’s F/A-18E/F "Super Hornet" and the Marine Corps’ MV-22 “Osprey.”
Aerosols
Another technology being developed is the use of aerosols as extinguishing agents.
These take advantage of the well established fire suppression capability of solid
particulates – as demonstrated with dry chemicals - with the possibility of significantly
reducing the amount of residue associated with the current dry chemical agents. The
NFPA is in the process of forming a technical committee to write a standard for “Fine
Aerosol Extinguishing Technology” which will ultimately provide the guidance to
assure these types of systems are employed in a manner that is safe and beneficial to
society.
Halocarbon Based Compositions
There are two compositions that are receiving attention for some specialized fire protection systems
applications. Both consist of halocarbon and dry chemical components although neither
uses the same halocarbon or dry chemical.
a. HFC-227ea and Sodium Bicarbonate. The US Army has done work to develop
a new agent for the protection of the crew compartment in new models of armored
combat vehicles to take on the role that is being filled by halon 1301 in current vehicles.
The composition consists of 95% by weight HFC-227ea halocarbon agent together with
5% by weight sodium bicarbonate dry chemical. They have reported 26 that the sodium
bicarbonate additive significantly reduces the generation of hydrogen fluoride normally
found with the exposure of halocarbon agents to flames. They attribute this to the quick
flame knockdown provided by the sodium bicarbonate. The Army has indicated that it
has achieved a 40% increase in performance of the HFC-227ea with the addition of this
small amount of sodium bicarbonate. The US EPA is reviewing this composition for
addition to the SNAP list as an agent suitable for use in occupied areas.
b. Gelled Halocarbon and Dry Chemical Suspension. Similar to the earlier
composition, the dry chemical component in this composition enhances the fire
suppression capability of the HFC-236fa halocarbon component and reduces the
generation of HF during fire suppression. This product is marketed under the name
Envirogel. There are various compositions but one reported 27 is made up of 40% by
weight of the gelled ammonium polyphosphate and 60% by weight HFC-236fa. The
agent is on the US EPA SNAP list for use in occupied areas. It is not listed in National
Fire Protection Association Standard 2001, Standard on Clean agent Fire Extinguishing
Systems. Interest has been shown in several applications for this type of material, most
notably in aircraft lavatory bottles and aircraft portable extinguishers.
