Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
20 2 333 3
- 1 -
FIRE EXTINGUISHING METHODS AND BLENDS
UTILIZING HYDROFLUOROCARBONS
BACKGROUND OF THE INVENTION
Field of the Invention.
This invention relates to fire extinguishing
methods and blends utilizing higher fluorinated C2 and C3
saturated hydrofluorocarbons.
Description of the Prior Art.
The use of certain bromine, chlorine and
iodine-containing halogenated chemical agents for the
extinguishment of fires is common. These agents are in
general thought to be effective due to their interference
with the normal chain reactions responsible for flame
propagation. The most widely accepted mechanism far
flame suppression is the radical trap mechanism proposed
by Fryburg in Review of Literature Pertinent to Fire
Extinauishing Aq~ents and to Basic Mechanisms Involved in
Their Action, NACA-TN 2102 (1950). The finding that the
effectiveness of the halogens are on a molar basis in the
order C1<Br<I supports the radical trap mechanism, as
reported by Malcom in Vaporizing Fire Extinctuishinq
Agents, Report 117, Dept. of Army Engineering Research
and Development Laboratories, Fort Bevoir, VA, 1950
(Project- 8-76-04-003). It is thus generally accepted
that compounds containing the halogens C1, Br and I act
by interfering with free radical or ionic species in the
flame and that the effectiveness of these halogens is in
the order I>Br>C1.
In contrast, hydrofluorocarbons (i.e.,
compounds containing only C, H and F atoms) have not
heretofore been recognized to display any chemical action
in the suppression of combustion. Thus, it is generally
A
24 2 333 3
- 2 -
thought that to be effective as a fire extinguishing
agent, a compound must contain C1, Br or I.
The use of iodine-containing compounds as fire
extinguishing agents has been avoided primarily due to
the expense of their manufacture or due to toxicity
considerations. The three fire extinguishing agents
presently in common use are all bromine-containing
compounds, Halon 1301 (CF3Br), Halori 1211 (CF2BrCl) and
Halon 2402 (CFZBrCFZBr). The effectiveness of these
three volatile bromine-containing compounds in
extinguishing fires has been described in U.S. Patent
4,014,799 to Owens. Although not employed commercially,
certain chlorine-containing compounds are also known to
be effective extinguishing agents, for example Halon 251
(CF3CF2C1) as described by Larsen in U.S. Patent
3,844,354.
Although the above named bromine-containing
Halons are effective fire fighting agents, those agents
containing bromine or chlorine are asserted by some to be
capable of the destruction of the earth's protective
ozone layer. Also, because the agents contain no
hydrogen atoms which would permit their destruction in
the troposphere, the agents may also contribute to the
greenhouse warming effect.
It is therefore an object of this invention to
provide a method for extinguishing fires that
extinguishes fires as rapidly and effectively as the
techniques employing presently used Halon agents while
avoiding the above-named drawbacks.
It is a further object of this invention to
provide an agent for the use in a method of the character
described that is efficient, economical to manufacture,
and environmentally safe with regard to ozone depletion
and greenhouse warming effects.
It is a still further object of this invention
to provide blends of hydrofluorocarbons and other fire
extinguishing agents that are effective and
A
- 3 -
environmentally safe.
20 2333 3
- 4 -
SUMMARY OF THE INVENTION
The foregoing and other objects, advantages and
features of the present invention may be achieved by
employing saturated, higher fluorinated
hydrofluorocarbons and blends thereof with other agents
as fire extinguishants for use in fire extinguishing
methods and apparatus. More particularly, the method of
this invention involves introducing to a fire a saturated
CZ or C3 higher fluorinated hydrofluorocarbon in a fire
extinguishing concentration and maintaining such
concentration until the fire is extinguished. Saturated
higher fluorinated hydrofluorocarbons of this invention
include compounds of the formula CxHyFz, where x is 2 or
3; y is 1 or 2; and z is 5, 6 or 7; where y is 1 and z is
5 when x is 2 and where z is 6 or 7 when x is 3.
Specific hydrofluorcarbons useful in accordance with this
invention include heptaf loot opropane ( CF3CHFCF;) ,
1, 1, 1, 3, 3, 3-hFx.afluorapropane (CF3CH~CF3) ,
1, 1, 1,'2, 3, 3-hexafluoropropar_e (CF3CHFCHF2) and
pentafluoroethane (CF3CHF2) . These hydrofluorocarbons
may be used alone, in admixture with each other or as
blends with other fire extinguishing agents. Generally,
the agents of this invention are employed at
concentrations lying in the range of about 3 to 15%,
preferably 5 to 10%, on a v/v basis.
2023333
- 5 -
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In accordance with the present invention,
saturated higher fluorinated C2 and C3 hydrofluorocarbons
have been found to be effective fire extinguishants at
concentrations safe for use. However, because such
hydrofluorocarbons contain no bromine or chlorine, they
have an ozone depletion potential of zero. Furthermore,
since the compounds contain hydrogen atoms, they are
susceptible to breakdown in the lower atmosphere and
hence do not pose a threat as greenhouse warming gasses.
Specific hydrofluorocarbons useful in
accordance with this invention are compounds of the
formula CxHyFz, where x is 2 or 3 ; y is 1 or 2 ; and z is
5, 6 or 7; where y is 1 and z is 5 when x is 2; and where
z is 6 or 7 when x is 3. Specific hydrofluorcarbons
useful in accordance with this invention include
heptafluoropropane (CF3CHFCF3), 1,1,1,3,3,3-hexafluoro-
propane (CF3CHZCF3), 1,1,1,2,3,3-hexafluoropropane
( CF3CHFCHF2 ) , and pentaf luoroethane ( CF3CHFz ) .
These compounds may be used alone or in
admixture with each other or in blends with other fire
extinguishing agents. Among the other agents with which
the hydrofluorocarbons of this invention may be blended
are chlorine and/or bromine containing compounds such as
Halon 1301 (CF3Br), Halon 1211 (CF2BrCl), Halon 2402
(CFZBrCFZBr) , Halon 251 (CF3CFZC1) and CF3CHFBr. Mixtures
of heptafluoropropane and Halon 1201 (CF2HBr) are
especially preferred because the compounds have similar
vapor pressures over a wide range of temperatures and
therefore the composition of the mixture remains
relatively constant during discharge or other
application.
Where the hydrofluorocarbons of this invention
are employed in blends, they are desirably present at a
level of at least about 10 percent by weight of the
blend. The hydrofluorocarbons are preferably employed at
higher levels in such blends so as to minimize the
2023333
- 6 -
adverse environmental effects of chlorine and bromine
containing agents.
The hydrofluorocarbon compounds used in
accordance with this invention are non-toxic and are
economical to manufacture. For example,
heptafluoropropane may be conveniently produced via the
reaction of commercially available hexafluoropropene
(CF3CF=CF2) with anhydrous HF as described in U.K. Patent
902,590. Similarly, 1,1,1,3,3,3-hexafluoropropane may be
synthesized by reacting anhydrous HF with
pentaf luoropropene ( CF3CH=CFz ) .
1,1,1,2,3,3-hexafluoropropane may be obtained by
hydrogenation of hexafluoropropene (CF3CF=CF2).
Pentafluoroethane may be obtained by the addition of
hydrofluoric acid to tetrafluoroethylene (CF2=CFZ) .
The saturated highly fluorinated CZ and C3
hydrofluorocarbons of this invention may be effectively
employed at substantially any minimum concentrations at
which fire may be extinguished, the exact minimum level
being dependent on the particular combustible material,
the particular hydrofluorocarbon and the combustion
conditions. In general, however, best results are
achieved where the hydrofluorocarbons or mixtures and
blends thereof are employed at a level of at least about
3% (v/v). Where hydrofluorocarbons alone are employed,
best results are achieved with agent levels of at least
about 5% (v/v). Likewise, the maximum amount to be
employed will be governed by matters of economics and
potential toxicity to living things. About 15% (v/v)
provides a convenient maximum concentration for use of
hydrofluorocarbons and mixtures and blends thereof in
occupied areas. Concentrations above 15 % (v/v) may be
employed in unoccupied areas, with the exact level being
determined by the the particular combustible material,
the hydrofluorocarbon (or mixture or blend thereof)
chosen and the conditions of combustion. The preferred
concentration of the hydrofluorocarbon agents, mixtures
20 2333 3
and blends in accordance with this invention lies in the
range of about 5 to 10% (v/v).
Hydrofluorocarbons may be applied using
conventional application techniques and methods used for
Halons such as Halon 1301 and Halon 1211. Thus, these
agents may be used in a total flooding fire extinguishing
system in which the agent is introduced to an enclosed
region (e.g., a room or other enclosure) surrounding a
fire at a concentration sufficient to extinguish the
fire. In accordance with a total flooding system
apparatus, equipment or even rooms or enclosures may be
provided with a source of agent and appropriate piping,
valves, and controls so as automatically and/or manually
to be introduced at appropriate concentrations in the
event that fire should break out. Thus, as is known to
those skilled in the art, the fire extinguishant may be
pressurized with nitrogen or other inert gas at up to
about 600 psig at ambient conditions.
Alternatively, the hydrofluorocarbon agents may
be applied to a fire through the use of conventional
portable fire extinguishing equipment. It is usual to
increase the pressure in portable fire extinguishers with
nitrogen or other inert gasses in order to insure that
the agent is completely expelled from the the
extinguisher. Hydrofluorocarbon containing systems in
accordance with this invention may be conveniently
pressurized at any desirable pressure up to about 600
psig at ambient conditions.
Practice of the present invention is
illustrated by the following Examples, which are
presented for purposes of illustration but not of
limitation.
EXAMPLE 1
A 28.3 cubic litre test enclosure was
constructed for static flame extinguishment tests (total
flooding). The enclosure was equipped with a Plexiglas
viewport and an inlet at the top for the agent to be
20 2333 3
_8_
tested and an inlet near the bottom to admit air. To
test the agent, a 90 x 50 mm glass dish was placed in the
center of the enclosure and filled with 10 grams of
cigarette lighter fluid available under the trademark
RONSONOL. The fuel was ignited and allowed a 15 second
preburn before introduction of the agent. During the
preburn, air was admitted to the enclosure through the
lower inlet. After 15 seconds, the air inlet was closed
and the fire extinguishing agent was admitted to the
enclosure. A predetermined amount of agent was delivered
sufficient to provide 6.6% v/v concentration of the
agent. The extinguishment time was measured as the time
between admitting the agent and extinguishment of the
flame. Average extinguishment times for a 6.6% v/v
concentration of heptafluoropropane, Halon 1301, Halon
1211 and CF3CHFBr are given in Table 1.
EXAMPLE 2
The experimental procedure of Example 1 was
carried out employing heptane as the fuel. The average
extinguishment times for 6.6% v/v of the same agents are
also given in Table 1.
Table 1
Extinguishment Time (seconds) for 6.6 % v/v Agent
Agent Lighter fluid n-Heptane
CF3CHFCF3 1. 6 1. 6
CF3Br 0 . 8 1. 4
(Halon 1301)
CFZBrCl 1.3 1.7
(Halon 1211)
CF3CHFBr 1. 0 1. 7
The Table shows the extinguishment time
required for various fuels at 6.6% v/v of the agents
employed. At this level, heptafluoropropane is as
effective as bromine-containing Halons in extinguishing
20 2333 3
_ g -
an n-heptane flame and nearly effective as the other
agents in extinguishing lighter fluid flames.
Levels of about 5-l0% are preferred for general
application of pure hydrofluorocarbons in accordance with
this invention. The use of too little agent results in
failure to extinguish the fire and can result in
excessive smoke and probably release of HF due to
combustion of the agent. The use of excessive amounts is
wasteful and can lead to dilution of the oxygen level of
the air to levels harmful to living things.
EXAMPLE 3
Example 1 was repeated with two white mice
admitted to the chamber. After extinguishment, mice were
exposed to combustion products for a total of 10 minutes
before being removed from the chamber. All mice showed
no ill effects during the exposure and appeared to behave
normally after removal from the apparatus.
EXAMPLE 4
Dynamic burn test data for heptafluoropropane
and 1,1,1,2,3,3-hexafluoropropane were obtained using the
cup burner test procedure in which air and n-butane are
continuously supplied to a flame produced in a glass cup
burner. Vapor of the agent to be tested was mixed with
air and introduced to the flame, with the concentration
of agent being slowly increased until the flow was just
sufficient to cause extinction of the flame. Data were
obtained in this manner for heptafluoropropane and
1,1,1,2,3,3-hexafluoropropane and, for comparative
purposes, for the following other Halon agents: Halon
1301 (CF3Br) ; Halon 1211 (CFZBrCl) ; Halon 251 (CF3CFZC1) ;
Halon 25 (CF3CFZH); and Halon 14 (CF4). The percent of
each agent in air (v/v) required to extinguish the flame
is given in Table 2.
2023333
- 10 -
TABLE 2
Extinguishment n-Butane Diffusion
of Flames
Air flow Agent Required Agent In
Air
Agent cc/min cc/min
o v/v
Halon 1301 16,200 396 2.4
( CF3Br )
Halon 1211 16,200 437 2.7
( CFZBrCl
)
Halon 251 16,200 963 5.9
( CF3CF2C1
)
CF3CHFCF3 16, 200 976 6. 0
CF3CHFCHFZ 16,200 1312 8.1
Halon 25 16,200 1409 8.7
( CF3CFZH
)
Halon 14 16,200 2291 14.1
(CF4)
EXAMPLE 5
Heptafluoropropane Halon 1211
and Halon
1301,
and Halon were used extinguish n-heptane
251 to diffusion
flames using the method Example 4. Test data are
of
reported in able 3.
T
2023333
- 11 -
TABLE 3
Extinguishment of n-Heptane Diffusion Flames
Air flow Agent Required Agent In
Air
Agent cc/min cc/min
v/v
Halon 1301 16,200 510 3.1
( CF3Br )
Halon 1211 16,200 546 3.4
( CFZBrC 1 )
Halon 251 16,200 1,006 6.2
( CF3CFZC1 )
CF3CHFCF3 16, 200 1, 033 6. 4
Halon 25 16,200 1,506 9.3
( CF3CFZH )
The dynamic test data reported in Tables 2 and
3 demonstrate that use of heptafluoropropane,
1,1,1,2,3,3-hexafluoropropane and pentafluoroethane in
accordance with this invention is significantly more
effective than other known non-bromine or chlorine
containing Halons such as Halon 14 (CF4). Moreover,
heptafluoropropane is comparable in effectiveness to
Halon 251, a chlorine containing chlorofluorocarbon. The
latter relationship is shown with respect to n-heptane as
well as n-butane fuels. While bromine and
chlorine-containing agents such as Halon 1301 and Halon
1211 are somewhat more effective than the hydrofluoro-
carbon agents under the cup burner test, the use of the
agents in accordance with this invention remains highly
effective and their use avoids the significant
environmental handicaps encountered with chlorine and
bromine containing Halons such as Halon 1301, Halon 1211,
and Halon 251.
20 2333 3
- 12 -
EXAMPLE 6
Static box flame extinguishment data were
obtained for 1,1,1,3,3,3-hexafluoropropane with a 35.2
litre test enclosure using the procedure of Example 1.
In addition to 1,1,1,3,3,3-hexafluoropropane, for
comparative purposes, Halon 1301, Halon 1211 and
Halon 251 were also tested. All agents were delivered at
a test concentration of 5.5% (v/v).
TABLE 4
Extinguishment Time (Seconds) for 5.5% (v/v) Agent
Aaent Extinction Times)
Halon 1301 1.02
(CF3Br)
15 Halon 1211 1.76
( CFZBrCl )
Halon 251 2.15
( CF3CF2C1 )
CF3CHZCF3 2 . 9 8
The data of Table 4 demonstrates that
1,1,1,3,3,3-hexafluoropropane is a highly effective fire
extinguishant. It is nearly as effective as Halon 251, a
chlorofluorocarbon, and it is sufficiently effective,
25 when compared to bromine containing Halons such as
Halon 1301 and Halon 1211, that it is preferable by
reason of the absence of ozone depletion and other
environmental effects of the chlorine and bromine
containing Halons.
30 In addition to being a highly effective agent
for extinguishing fires, 1.1.1.2.3.3-hexafluoropropane at
concentrations in accordance with the method of this
invention is well within the range of toxicological
safety.
35 The following Examples demonstrate the
effective use of hydrofluorocarbon agents in accordance
2023333
- 13 -
with this invention in mixtures or blends including
bromine-containing Halon fire extinguishants.
EXAMPLE 7
Dynamic test data using the cup burner
procedure of Example 4 were obtained for various mixtures
of heptafluoropropane and Halon 1201 (CF2HBr). Air and a
mixture of the agents were continuously supplied to an
n-heptane diffusion flame produced in a glass cup burner.
For a given heptafluoropropane flow, the flow of CFZHBr
was slowly increased until the flow was just sufficient
to cause extinction of the flame. The experiment was
repeated at various heptafluoropropane flow rates, and
the results are reported in Table 6.
Table 6 reports the actual volume percent in
air as observed. Table 6 also reports the calculated
weight percent heptafluoropropane in the mixture. In
addition, Table 6 also reports the ozone depletion
potential ("ODP") for each agent. ODP data for Halon 1201
was calculated in the following manner. ODP's for pure
compounds were calculated by the following formula:
ODP = A E P [(#C1)B + C(#Br)] D(#C-1)
In this expression, P is the photolysis factor. P=1.0 if
there are no special structural features which make the
molecule subject to tropospheric photolysis. Otherwise,
P=F, G, or H, as indicated in the table of constants,
Table 5 below.
TABLE 5
CONSTANT NAME VALUE
F Photolysis factor for geminal Br-C-C1 0.180
G Photolysis factor for geminal Br-C-Br 0.015
H Photolysis factor for adjacent BR-C-C-Br0.370
A Normalizing constant 0.446
B Exponent for chlorine term 0.740
C Multiplier for bromine 32.000
term
D Constant for carbon term 1.120
E Hydrogen factor [=1.0 for no H's] .0625
2023333
- 14 -
ODP's for the mixtures were obtained by
multiplying the weight percent of the Halon 1201 by the
ODP of pure Halon 1201.
TABLE 6
Extinguishment of n-Heptane Diffusion Flames
CF3CHFCF3 / CF2HBr Mixtures
Flow at
Extinguishment
cc/min Volume % in Air
Total Weight %
CF3CHFCF3 CF2HBr CF3CHFCF3 CF2HBr Vol % CF3CHFCF3 ODP
0 1380 0 4.0 4.0 0 0.89
164 489 1.0 3.0 4.0 30.1 0.62
353 357 2.2 2.2 4.4 56.5 0.39
533 216 3.3 1.3 4.6 76.6 0.21
705 122 4.3 0.8 5.1 87.4 0.11
869 39 5.4 0.2 5.6 97.2 0.02
1042 0 6.4 0 6.4 100.0 0.00
These data demonstrate that effective flame
extinguishment may be obtained with mixtures of
heptafluoropropane and Halon 1201 and that the ODP of
Halon 1201 can be materially reduced by providing
heptafluoropropane therewith.
20 2333 3
- 15 -
EXAMPLES 8-11
Tables 7, 8, 9 and 10 report diffusion flame
extinguishment data obtained using the method of Example
7 for the following agent mixtures:
Table 7 - heptafluoropropane and Halon 1211
( CF2BrC1 )
( CF3Br )
Table 8 - heptafluoropropane and Halon 1301
Table 9 - pentafluoroethane and Halon 1201
( CFZHBr )
Table 10- 1,1,1,2,3,3-hexafluoropropane and
Halon 1201 (CFZHBr)
These Tables also contain ODP data for pure
Halons 1211 and 1301 as reported by the Lawrence
Livermore Research Laboratories. ODP's for Halon 1201
were calculated using the method given above, and ODP's
for the mixtures were obtained by multiplying the weight
percent of the Halon agent by the ODP of the pure Halon.
TABLE 7
Extinguishment of n-Heptane Diffusion Flames
CF3CHFCF3 / CFZBrCl Mixtures
Flow at
2 5 Extinguishment
cc/min Volume ~ in
Air
Total Weight
CF3CHFCF3 CFZBrClCF3CHFCF3 CFZBrClVol $ CF3CHFCF3 ODP
0 546 0 3.4 3.4 0 2.64
164 437 1.0 2.7 3.7 27.5 1.91
262 378 1.6 . 2.3 3.9 41.7 1.54
353 328 2.2 2.0 4.2 53.1 1.24
533 210 3.3 1.3 4.6 72.5 0.73
705 109 4.3 0.7 5.0 86.3 0.36
869 44 5.4 0.2 5.6 94.9 0.13
1042 0 6.4 0 6.4 100.0 0.00
20 2333 3
- 16 -
TABLE 8
Extinguishment of n-Heptane Diffusion Flames
CF3CHFCF3 / CF3Br Mixtures
Flow at
Extinguishment
cc/min Volume % in Air
Total Weight
%
CF3CHFCF3CF3Br CF3CHFCF3 CF3Br Vol % CF3CHFCF3 ODP
0 510 0 3.1 3.1 0 14.28
164 422 1.0 2.6 3.6 30.4 9.93
262 334 1.6 2.1 3.7 46.4 7.65
353 317 2.2 1.9 4.1 57.1 6.13
533 246 3.3 1.5 4.8 71.6 4.06
705 98 4.3 0.6 4.9 89.2 1.54
869 51 5.4 0.3 5.7 95.4 0.66
943 24 5.8 0.1 6.0 98.5 0.21
1042 0 6.4 0 6.4 100.0 0.00
20 2333 3
- 17 -
TABLE 9
Extinguishment of n-Heptane Diffusion Flames
CF3CFZH / CF2HBr Mixtures
Flow at
Extinguishment
cc/min Volume % in Air
Total Weight %
CF,CF.,H CF,.HBr CF_CF..H CF_HBr Vol ~: CF_CF_H OnP
0 1380 0 4.0 4.0 0 0.89
196 526 1.2 3.2 4.4 25.6 0.66
314 470 1.9 2.9 4.8 37.5 0.56
421 423 2.6 2.6 5.2 47.7 0.46
637 338 3.9 2.1 6.0 63.0 0.33
1039 109 6.4 0.7 7.1 89.4 0.09
1509 0 9.3 0 9.3 100.0 0.00
TABLE 10
Extinguishment of n-Heptane Diffusion Flames
CF3CHFCFZH / CFZHBr Mixtures
Flow at
Extinguishment
cc/min Volume % in Air
Total Weight
%
CF3CHFCFZH CFZHBrCF3CHFCFZH CFZHBr Vol CF3CHFCF2HODP
%
0 1380 0 4.0 4.0 0 0.89
196 508 1.2 3.1 4.3 30.8 0.62
421 423 2.6 2.6 5.2 53.7 0.41
637 367 3.9 2.3 6.2 66.3 0.30
843 207 5.2 1.3 6.5 82.1 0.16
2023333 --
- 18 -
The data of Tables 7 through 10 demonstrate
that various mixtures of hydrofluorocarbons in accordance
with this invention with chlorine and/or
bromine-containing Halons are effective flame
extinguishment agents and that significant reductions in
ODP of the chlorine and/or bromine containing materials
can be obtained by admixture thereof with
hydrofluorocarbons in accordance with this invention.
Saturated higher fluorinated CZ and~C3 hydrofluorocarbons
such as heptafluoropropane,
1,1,1,2,3,3-hexafluoropropane,
1,1,1,3,3,3-hexafluoropropane and pentafluoroethane, like
the presently employed chlorine and bromine-containing
Halons, are nondestructive agents, and are especially
useful where cleanup of other media poses a problem.
Some of the applications of the hydrofluorocarbons of
this invention are the extinguishing of liquid and
gaseous fueled fires, the protection of electrical
equipment, ordinary combustibles such as wood, paper and
textiles, hazardous solids, and the protection of
computer facilities, data processing equipment and
control rooms.
