Fire extinguishers – Processes – Of extinguishing fire
Reexamination Certificate
2000-09-18
2002-07-16
Doerrler, William (Department: 3752)
Fire extinguishers
Processes
Of extinguishing fire
C169S045000, C169S047000, C169S043000
Reexamination Certificate
active
06419027
ABSTRACT:
FIELD OF THE INVENTION
The invention described and claimed herein is generally related to chemical agents used for fire extinguishment, explosion suppression, explosion inertion, and fire inertion and more particularly, to extinguishing, suppressing, and inerting fluoroalkylphosphorus agents that are replacements for halon fire and explosion suppressants and extinguishants. The production of halons has been eliminated or curtailed in many nations due to their impact on stratospheric ozone.
BACKGROUND OF THE INVENTION AND PRIOR ART
The broad class of halocarbons consists of all molecules containing carbon and one or more of the following halogen atoms: fluorine, chlorine, bromine, and/or iodine. Halocarbons may also contain other chemical features such as hydrogen atoms, carbon-to-carbon multiple bonds, or aromatic rings. Haloalkanes, a subset of halocarbons, contain only single bonds between the carbon atoms. The use of certain haloalkanes as fire extinguishing agents has been known for many years.
For example, fire extinguishers containing carbon tetrachloride and methyl bromide were used in aircraft applications as early as the 1920s. Over a period of years the high toxicity of these compounds was recognized and they were replaced with less toxic compounds. Chlorobromomethane was used in aircraft applications from the 1 950s to the 1 970s. A major study of haloalkanes as fire extinguishing agents was conducted by the Purdue Research Foundation for the U.S. Army from 1947 to 1950 (FIRE EXTINGUISHING AGENTS, Final Report, Purdue University, 1950). Haloalkanes used for fire protection are often designated by the “halon numbering system.” This system gives in order the number of atoms of carbon, fluorine, chlorine, and bromine in the molecule. Thus, for example, CBrCIF2, whose chemical name is bromochlorodifluoromethane, is often referred to as Halon 1211.
The term “extinguishment” is usually used to denote complete elimination of a fire; whereas, “suppression” is often used to denote reduction, but not necessarily total elimination, of a fire or explosion. These two terms are sometimes used interchangeably. There are four general types of halocarbon fire and explosion protection applications. (1) In total-flood fire extinguishment and/or suppression applications, the agent is discharged into a space to achieve a concentration sufficient to extinguish or suppress an existing fire. This is often, though not always, done by an automatic system, which detects the fire and then automatically discharges the extinguishing agent to fill the space with the concentration of a gaseous or an evaporated volatile liquid agent to the concentration needed to suppress or extinguish the contained fire. Total flooding use includes protection of enclosed, potentially occupied spaces such as computer rooms as well as specialized, often unoccupied spaces such as aircraft engine nacelles and engine compartments in vehicles. Note that the term “total flood” does not necessarily mean that the extinguishing or suppressing agent is uniformly dispersed throughout the space protected. (2) In streaming applications, the agent is applied directly onto a fire or into the region of a fire. This is usually accomplished using manually operated wheeled or portable units. A second method, which we have chosen to include as a streaming application, uses a “localized” system, which discharges agent toward a fire from one or more fixed nozzles. Localized systems may be activated either manually or automatically. (3) In explosion suppression, a halocarbon is discharged to suppress an explosion that has already been initiated. The term “suppression” is normally used in this application since the explosion is usually self-limiting. However, the use of this term does not necessarily imply that the explosion is not extinguished by the agent. In this application, a detector is usually used to detect an expanding fireball from an explosion, and the agent is discharged rapidly to suppress the explosion. Explosion suppression is used primarily, but not solely, in defense applications. (4) In inertion, a halocarbon is discharged into a space to prevent an explosion or a fire from being initiated. Often, a system similar or identical to that used for total-flood fire extinguishment or suppression is used. Inertion is widely used for protection of oil production facilities at the North Slope of Alaska and in other areas where flammable gases or explosive dusts may build up. Usually, the presence of a dangerous condition (for example, dangerous concentrations of flammable or explosive gases) is detected, and the halocarbon is then discharged to prevent the explosion or fire from occurring until the condition can be remedied.
Thus, there are four fire and explosion protection applications covered by this disclosure:
1. Total-Flood Fire Extinguishment and Suppression
2. Streaming Fire Extinguishment and Suppression
3. Explosion Suppression
4. Explosion and Fire Inertion
The halogenated chemical agents currently in use for fire extinguishment (by total flooding or streaming), explosion suppression, explosion inertion, and fire inertion are generally bromine-containing haloalkanes. Such chemicals contain bromine, fluorine, and carbon (and, in at least one case, chlorine), contain no hydrogen atoms, and have only single bonds between atoms. These chemicals include Halon 1202 (CBr
2
F
2
), Halon 1211 (CBrCIF
2
), Halon 1301 (CBrF
3
), and Halon 2402 (CBrF
2
CBrF
2
). Information on the most important of the existing halons are shown in Table I. The “CAS No.” is the number assigned by the Chemical Abstract Services of the American Chemical Society to aid in identifying chemical compounds. Halon 1301 (bromotrifluoromethane) and Halon 1211 (bromochlorodifluoromethane) are the most widely used haloalkane fire extinguishing agents. Halon 1301 is widely used for total-flood fire extinguishment, explosion suppression, and inertion. Due to its higher boiling point and higher toxicity, Halon 1211 is usually not used in total-flood applications, but, it is widely used in streaming.
TABLE I
EXISTING HALONS.
Hal-
Boiling
on
Point,
Name
Formula
No.
CAS No.
° C.
dibromodifluoromethane
CBr
2
F
2
1202
75-61-6
24.5
bromochlorodifluoromethane
CBrClF
2
1211
353-59-3
−4
bromotrifluoromethane
CBrF
3
1301
75-63-8
−58
1,2-dibromotetrafluoroethane
CBrF
2
CBrF
2
2402
124-73-2
47
Bromine-containing haloalkanes such as the existing halons operate as fire extinguishing agents by a complex chemical reaction mechanism involving the disruption of free-radical chain reactions, which are essential for continuing combustion. The existing halons are desirable as fire extinguishing agents because they are effective, because they leave no residue (i.e., they are liquids that evaporate completely or they are gases), and because they do not damage equipment or facilities to which they are applied.
Recently, however, halons, have come to be recognized as serious environmental threats due to their ability to cause stratospheric ozone depletion. In the United States, production of the existing halons (Halon 1201, Halon 1301, Halon 121 1, and Halon 2402) stopped at the end of 1993.
Much research has gone on to find replacements for the existing halons for protection against fires and explosions; however, the search for halon replacements has been less than totally successful (“Pressure Mounts As Search for Halon Replacements Reaches Critical Phase,” Chemical and Engineering News, Sep. 19,1994, pp. 29-32). Most of the agents now being promoted as halon replacements are hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), and perfluorocarbons (FCs or PFCs). HCFCs, HFCs, and FCs (PFCs) appear to operate primarily by heat absorption, which is a less effective mechanism for most fire and explosion protection applications than the free radical chain disruption mechanism used by the existing halons. Thus, HCFCs, HFCs, and FCs (a family that we refer to as “first-generation” halon replacements) have a significantly decreased effectiveness compared to the halons now
Becker R W
Doerrler William
GlobeTech Inc.
Hwu Davis
R W Becker & Associates
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