Compositions – Fire-extinguishing – Volatile or gas charged liquids containing
Reexamination Certificate
2001-09-18
2002-10-08
Anthony, Joseph D. (Department: 1714)
Compositions
Fire-extinguishing
Volatile or gas charged liquids containing
C252S002000, C252S003000
Reexamination Certificate
active
06461530
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of fire extinguishing compositions and methods for delivering a fire extinguishing composition to or within a protected hazard area.
DESCRIPTION OF THE PRIOR ART
Certain halogenated hydrocarbons have been employed as fire extinguishants since the early 1900's. Prior to 1945, the three most widely employed halogenated extinguishing agents were carbon tetrachloride, methyl bromide and bromochloromethane. For toxicological reasons, however, the use of these agents has been discontinued. Until only recently, the three halogenated fire extinguishing agents in common use were the bromine-containing compounds, Halon 1301 (CF
3
Br), Halon 1211 (CF
2
BrCl) and Halon 2402 (BrCF
2
CF
2
Br). One of the major advantages of these halogenated fire suppression agents over other fire suppression agents such as water or carbon dioxide is the clean nature of their extinguishment. Hence, the halogenated agents have been employed for the protection of computer rooms, electronic data processing facilities, museums and libraries, where the use of water for example can often cause more secondary damage to the property being protected than the fire itself causes.
Although the above named bromine and chlorine-containing compounds are effective fire fighting agents, those agents containing bromine or chlorine are asserted to be capable of the destruction of the earth's protective ozone layer. For example, Halon 1301 has an Ozone Depletion Potential (ODP) rating of 10, and Halon 1211 has an ODP of 3. As a result of concerns over ozone depletion, the production and sale of these agents after Jan. 1, 1994 is prohibited under international and United States policy.
It is therefore an object of the present invention to provide a method for extinguishing fires which does not employ bromine or chlorine-containing agents and which does not lead to the depletion of stratospheric ozone.
The use of hydrofluorocarbons (HFCs), for example 1,1,1,2,3,3,3-heptafluoropropane (CF
3
CHFCF
3
), as fire extinguishing agents has been proposed only recently (see for example, M. Robin, “Halogenated Fire Suppression Agents,” in Halon Replacements, A. W. Miziolek and W. Tsang, eds., ACS Symposium Series 611, ACS, Washington, D.C., 1995). Since the hydrofluorocarbons do not contain bromine or chlorine, the compounds have no effect on the stratospheric ozone layer and their ODP is zero. As a result, hydrofluorofluorocarbons such as 1,1,1,2,3,3,3-heptafluoropropane and pentafluoroethane (CF
3
CF
2
H) are currently being employed as environmentally friendly replacements for the Halons in fire suppression applications.
The hydrofluorocarbon fire suppression agents are not as efficient on a weight basis as the Halon agents and hence increased weights of the hydrofluorocarbon agents are required to protect a given space; in some cases the weight of hydrofluorocarbon agent required is twice that of the Halon agent. A further disadvantage of the hydrofluorocarbon fire suppression agents compared to the Halon agents is their relatively high cost. The relatively high agent cost and lowered efficiency associated with the hydrofluorocarbon fire suppression agents leads to suppression system costs which are much higher compared to systems employing the Halon agents.
It is therefore a further object of the present invention to provide a fire suppression method which reduces the amount of hydrofluorocarbon fire suppression agent required for fire suppression, hence reducing the overall cost of the fire suppression system compared to conventional hydrofluorocarbon fire suppression systems.
When employed for the extinguishment of very large fires, the hydrofluorocarbon fire suppression agents react in the flame to form various amounts of the decomposition product HF, the relative amounts formed depending on the particular fire scenario. In larger quantities, HF can be corrosive to certain equipment and also poses a threat to personnel.
It is therefore a further object of this invention to provide a method for suppression fire which reduces the amount of decomposition products formed from the hydrofluorocarbon fire suppression agents.
In addition to the hydrofluorocarbon agents, inert gases have been recently proposed as replacements for the Halon fire suppression agents (see for example, T. Wysocki, “Inert Gas Fire Suppression Systems Using IG541 (INERGEN): Solving the Hydraulic Calculation Problem,” Proceedings of the 1996 Halon Options Technical Working Conference, Albuquerque, N. Mex., May 7-9, 1996). Pure gases such as nitrogen or argon, and also blends such as a 50:50 blend of argon and nitrogen have been proposed.
The inert gas agents are very inefficient at fire suppression, and as a result vast amounts of the inert gas agent must be employed to provide extinguishment. Typical extinguishing concentrations for inert gas agents range from 45 to over 50% by volume, compared to ranges of 5-10% by volume for hydrofluorocarbon fire suppression agents. The large amounts of agent required in the case of the inert gases results in the need for a much larger number of storage vessels compared to the case of the hydrofluorocarbon agents, and as a result large storage areas are required to contain the inert gas system cylinders. For example, in certain situations requiring a single cylinder of a hydrofluorocarbon agent, up to 50 cylinders of an inert gas agent may be required.
It is therefore a further object of this invention to provide a method for suppression of fires which reduces the amount of inert gas required for the suppression of fires, thereby reducing the number of inert gas cylinders required for the protection of a given hazard and reducing the overall cost of the suppression system.
A further disadvantage of the inert gas systems is the high enclosure pressure developed during discharge due to the large amounts of gas which must be injected into the protected enclosure. This can lead to structural damage if the enclosure is not sufficiently vented to allow for leakage and pressure dissipation.
It is a therefore a further object of this invention to provide a method for the extinguishment of fires which reduces the amount of inert gas required to extinguish a fire, hence reducing the high pressure development.
Due to the large amounts of inert gas required for fire suppression, inert gas systems typically discharge their contents into the protected hazard over a one to two minute period. This compares to the case of the fluorocarbon agents, which, because they require much less gas, employ discharge times of 10 seconds or less. Fire extinguishment will not occur until the extinguishing concentration is achieved within the protected enclosure, and hence due to the long discharge times employed with the inert gas agents the fire burns much longer before extinction compared to the case of the fluorocarbon agents. Because the fire burns longer, increased amounts of combustion products are produced with inert gas systems. This is clearly undesirable as it is well documented that small amounts of combustion products (e.g. smoke) can cause extensive equipment damage, and many combustion products are toxic to humans in low concentrations.
It is a further object of the present invention to provide a method for the suppression of fires which reduces the extinguishment time compared to inert gas systems, resulting in reduced amounts of combustion products.
A further problem associated with the use of inert gas suppression agents is depletion of oxygen within the protected hazard to levels dangerous to humans. The amount of oxygen required to sustain human life, and therefore mammalian life, is well known, see for example, Paul Webb, Bioastronautics Data Book, NASA SP-3006, NASA, 1964, page 5. At normal atmospheric pressures at sea level, the unimpaired performance zone is in the range of about 16 to 36 volume percent oxygen. The discharge of the inert gas agents into an enclosure results in oxygen levels significantly below the level of unimpaired performance. For example,
Register W. Douglas
Robin Mark L.
Rowland Thomas F.
Anthony Joseph D.
Baker & Daniels
PCBU Services, Inc.
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