EXTINGUISHING MECHANISM FOR SOLID PROPELLANT BASED GAS
GENERATOR FIRE SUPPRESSION SYSTEM
William P. Sampson
Steven M. Robbins
Mark E. Ewing
ATK Aerospace Systems
Box 707
Brigham City, UT 84302
435-863-3084
[email protected]
ABSTRACT
ATK completed the development of a solid gas generant-based fire suppression system in 2009.
The project goals were to produce low temperature, low toxicity gases for use in occupied spaces
which had no environmental concerns and were highly effective suppression agents. This effort
required the development of some very unique pyrotechnic chemistry.
The pyrotechnic formulation that was developed generates a combination of nitrogen gas and
water vapor with small amounts of carbon dioxide. This combination works efficiently to
suppress fires by heat absorption in the flame front by means of the heat capacity of the gases
and the latent heat of vaporization of the condensed water. Since the gases generated are
transient in nature, due to the condensing water vapor, it is very difficult to perform standard cup
burner measurements. Therefore, theoretical calculations were pursued to quantify and explain
the extinguishing mechanism.
Calculations based on the approach taken in prior published research using thermodynamics
based calculations provide the basis for a theoretical explanation of the extinguishment
mechanism. By balancing the heat generated during combustion of specific fuels with the heat
absorption capability of the agent from the gas generant and other gases present, agent quantities
required for extinguishment were calculated. The calculated values for extinguishing
concentrations compare well with measured data. The theory predicts that a significant portion of
suppression must be provided by the heat of vaporization of condensed water. This addresses the
question of how much water in the vapor phase verses the liquid phase is involved in
extinguishment.
1
NOMENCLATURE
Cpi
Cpg
Δhfi, Δhfj
Δhcc
Δhvi
Δha, Δhb
t0
tfr
tfc
tex
vi, vj
vg
vair
fwc
Q
XG
MEC
heat capacity at constant pressure for component i, J/mol∙K
heat capacity at constant pressure for agent gases, J/mol∙K
heat of formation for component i or j at 298 K, kJ/mol
heat of combustion at standard conditions, calculated, J/mol
heat of vaporization for component i at standard conditions, J/mol
enthalpy change for component a or b, J/mol
standard temperature, 298 K
adiabatic flame temperature, reported, K
adiabatic flame temperature, calculated, K
extinction limit temperature, K
molar volume of component i or j, mol
stoichiometric coefficient of added inert gases, mol/mol fuel
stoichiometric coefficient of air, mol/mol-fuel
fraction of water in the agent that is in condensed phase
total heat, J
mole fraction in air of added inert gas agent at the MEC
minimum extinguishing concentration
SUMMARY
For many years the fire protection industry has provided effective systems that protect valuable
assets from fire by using chemical-based agents, referred to as special agents, including halon
and hydrofluorocarbons. While effective, there are concerns about the long-term environmental
acceptability of these agents, and alternates are being pursued. One alternate developed by ATK
is the OS-10 system. This system produces a combination of water vapor and nitrogen gas. This
fire suppressing agent is produced by a gas generator. To understand the fire suppression
mechanism and increase confidence in the suppression capability in various applications, a
theoretical model has been developed to provide insight into how the combination of these gases
works to suppress a fire.
The modeling approach taken assumes the extinguishing mechanism operates via heat
absorption. Water vapor and nitrogen gas are mostly inert under the conditions of interest,
eliminating the potential for chemical reaction-based inhibition. Also, other agents have been
successfully modeled in this manner, as described by Senecal.1 The steps taken to build and
validate the model are as follows:
1. Select the fuel to extinguish.
2. Utilize the NASA-Lewis CEA chemical equilibrium code2 to predict the combustion
products.
3. Verify the heat of combustion from the heat of formation for the various chemical
reactants and products involved in the combustion reaction.
4. Verify the adiabatic flame temperature by calculation using the heat capacities of the
combustion products. This exercise develops the relation between the flame temperature,
the heat produced, and the chemistry of the combustion reaction.
5. Then, modify the model to account for the addition of the water vapor and nitrogen gas
fire suppression agents. The flame temperature, heat produced, and heat adsorbed can
2
then be calculated for any given amount of agent added. The calculations are iterated to
find the volume of suppression agent required to absorb the heat produced and cool the
flame temperature to the characteristic extinction limit temperature of the fuel.
6. With the model calculating the volume of suppression agent required to extinguish the
flame, the percent oxygen remaining in the room is then calculated and compared to
measurements in actual tests.
The model was applied with heptane as the fuel and the combination of water vapor and nitrogen
gas produced by the OS-10 gas generators as the fire suppression gases. The predicted percent
oxygen in the room, at the point of extinguishment, by the model was 17.0 percent with a 30
percent condensed water fraction. Video shows that some of the gas is produced as a condensed
fog-like vapor during the initial discharge making a 30 percent condensed water fraction
reasonable. To compare with measured data, the extinguishing concentration was determined by
testing the OS-10 in a 100 m3 volume room. Two tests were run and oxygen levels were
measured at approximately 16.8 and 17.1 percent. This compares well to the predicted value and
substantiates that the extinguishing mechanism is via heat absorption.
BACKGROUND
Water vapor and nitrogen gas are well known as good fire suppressants with no threat to the
ozone or global warming. As such, there is an interest in using these gases as a long-term answer
to the need for environmentally sustainable fire suppression. One step in making them viable
candidates is to understand the extinguishing mechanism employed to suppress fires.
One source for these gases is a new technology that produces water vapor and nitrogen gas using
a gas generator. A gas generator contains a material that, when initiated, burns to produce the
effluent gases. Most gas generators burn materials that contain significant amounts of carbon and
have CO or CO2 in the effluent. A new patented gas generant formulation was developed that by
design has very small amounts of carbon in the effluent, which is key to making it usable in areas
that are occupied by people. The development began in the early 2000s when ATK was
exploring new applications for energetic materials developed for the automobile air bag industry.
By 2006, the feasibility of a fire suppression system had proven successful. Final design and
subsequent characterization testing was initiated to support receiving a favorable Department of
Transportation classification, Environmental Protection Agency Significant New Alternatives
Program approval for occupied spaces, and an Underwriters’ Laboratories listing – all three of
which have been accomplished.
As shown in Figure 1, the basic OS-10 system consists of two sections: the gas generator and a
heat management section. The dimensions are approximately 5.5 inches (14 cm) in diameter and
27 inches (68.6 cm) long.
The gas generator weighs approximately 24 lbs (10.9 kg) and, when initiated, produces at high
temperatures the gases shown in Table 1. A very small amount of particulates is also generated,
approximately 150 mg per cubic meter of volume in the protected space. The quantity and make
up of these particulates have been approved by the EPA for occupied space.
The heat management section then reduces the temperature of the gases by absorbing heat in
various media contained within the section. The type and amount of media affect the weight of
the system and the temperature of the gases. The weight of the heat management section varies
from 25 to 47 lbs (11.3 to 21.3 kg) and the gas exit temperatures vary from 140 to 350 °F (60 to
3
177 °C) depending on configuration. This ability to tailor the gas exit temperature allows for
raising or lowering the resulting final room temperature and humidity level after discharge,
depending on the application. The testing supporting this paper was performed using 22 lbs (10
kg) of steel shot as the heat absorption media with a corresponding weight for the heat
management section of 36 lbs (16.3 kg).
Gas Generator
Section
Heat Management
Section
Figure 1. Neptune Water Vapor/Nitrogen Gas Generator
Table 1. Agent Composition and Quantity per Gas Generator
Gas
Moles
Mole Fraction (%)
H2O
81.1
62.0
N2
44.6
34.1
CO2
3.44
2.63
H2
1.65
1.26
CO
0.02
0.01
To ta l
130.8
100
EXTINGUISHING MECHANISM
The extinguishing mechanism model was developed based on the heat absorption capacities of
the atmosphere and the products of combustion surrounding a heptane flame. As heat is absorbed
from the heptane flame, the flame temperature is reduced. When the flame temperature reaches
the extinction limit temperature for heptane, the flame goes out. The quantities and ratios of the
extinguishing environment can then be determined.
We start by calculating heptane thermodynamic flame properties using this theory.
General combustion of a hydrocarbon in air follows the equation:
4
𝐶𝑛 𝐻𝑚 + �𝑛 +
𝑚
𝑚
𝑚
� (𝑂2 + 3.76𝑁2 ) = 3.76 �𝑛 + � 𝑁2 + 𝑛𝐶𝑂2 + 𝐻2 𝑂
4
4
2
(1)
However, in practice, the combustion process always produces other minor products and
incomplete conversion of carbon to CO2. To achieve better fidelity, the NASA-Lewis CEA code2
was used to predict the full range of products. These are included in the model and used to
calculate both the heat of combustion and the combined heat capacity of the gases present at
extinguishment.
Heptane is used as a standard in the fire suppression industry where:
𝑛 = 7 𝑚𝑜𝑙
𝑚 = 16 𝑚𝑜𝑙
The heat of combustion is calculated by:
∆ℎ𝑐𝑐 =
𝑎
�
𝑖=𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠
�𝑣𝑖 ∆ℎ𝑓𝑖 � −
𝑏
�
𝑗=𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠
(𝑣𝑗 ∆ℎ𝑓𝑗 )
(2)
where the following subscripts are used throughout this document (Table 2):
Table 2. Subscripts Used in Equations for Reactants and Products
Subscript
Component
1
H2O
2
CO2
3
N2
4
C7H16
5
O2
6
CO
7
Ar
8
H2
9
OH
10
NO
11
H
12
O
The NASA-Lewis thermochemical code was run at stoichiometric oxygen levels and standard
conditions. The resulting volumetric combustion products predicted are shown in Table 3. The
heats of formations for the reactants and products were obtained from the NASA-Lewis database
and are also included in Table 3.
5
Table 3. NASA-Lewis Combustion Product Prediction and Heats of Formation
Component
1
2
3
4
5
6
7
8
9
10
11
12
Heat of Formation Δhf (KJ/mol)
-24.8
-393.5
0
-187.9
0
-110.5
0
0
39.3
91.3
218.0
249.2
Volume/Mole of Heptane (mol)
7.703
6.182
40.837
1
0.353
0.816
0.490
0.186
0.192
0.146
0.029
0.020
Substituting the output into the combustion equation (2):
∆ℎ𝑐𝑐 = (𝑣1 ∆ℎ𝑓1 + 𝑣2 ∆ℎ𝑓2 + 𝑣3 ∆ℎ𝑓3 + 𝑣5 ∆ℎ𝑓5 + 𝑣6 ∆ℎ𝑓6 + 𝑣7 ∆ℎ𝑓7 + 𝑣8 ∆ℎ𝑓8
+ 𝑣9 ∆ℎ𝑓9 + 𝑣10 ∆ℎ𝑓10 + 𝑣11 ∆ℎ𝑓11 + 𝑣12 ∆ℎ𝑓12 ) − [𝑣4 ∆ℎ𝑓4
𝑚
+ �𝑛 + � (∆ℎ𝑓5 + 3.76∆ℎ𝑓3 )]
4
based on 1 mol of heptane reacted.
(3)
∆ℎ𝑐𝑐 = −4139000 𝐽
The adiabatic flame temperature for heptane is calculated by the following equation:
𝐼
𝑄 = � �𝑣𝑖 �
𝑖=1
𝑡𝑓𝑐
𝑡0
𝐶𝑝𝑖 𝑑𝑡�
(4)
where:
𝑄 = −∆ℎ𝑐𝑐
Since gas heat capacities are a function of temperature, the Cp versus T coefficients were
obtained in polynomial form from the NASA-Lewis thermochemical database. The following
factors are divided into low-temperature LCp (<1,000 °K) (Table 4) and high-temperature HCp
(> =1,000 °K) (Table 5) regimes where the general heat capacity equation is in the form of:
𝐶𝑝 = 𝑅(𝐴 + 𝐵𝑇 + 𝐶𝑇 2 + 𝐷𝑇 3 + 𝐸𝑇 4 )
𝐽
𝑅 = 8.31451
𝑚𝑜𝑙 ∗ 𝐾
(5)
6
Table 4. Heat Capacity Coefficients for T<1,000 °K (LCp )
1
𝑨
4.1986
𝑩 𝒙 𝟏𝟎−𝟑
𝑪 𝒙 𝟏𝟎−𝟔
𝑫 𝒙 𝟏𝟎−𝟗
𝑬 𝒙 𝟏𝟎−𝟏𝟐
2
2.3568
8.9846
-7.1236
2.4592
-0.14370
3
3.5310
-0.12366
-0.50300
2.4353
-1.4088
5
3.7825
-2.9967
9.8473
-9.6813
3.2437
6
3.5795
-0.61035
1.0168
0.90701
-0.90442
7
2.5
0
0
0
0
8
2.3443
7.9805
-19.478
20.157
-7.3761
9
3.9920
-2.4013
4.6179
-3.8811
1.3641
10
4.2186
-4.6399
11.044
-9.3406
2.8055
11
2.5
0
0
0
0
12
3.1683
-3.2793
6.6431
-6.1281
2.1127
Component
-2.0364
6.5204
-5.4880
1.7720
Table 5. Heat Capacity Coefficients for T>=1,000 °K (HCp )
1
𝑨
2.6770
𝑩 𝒙 𝟏𝟎−𝟑
𝑪 𝒙 𝟏𝟎−𝟕
𝑫 𝒙 𝟏𝟎−𝟏𝟏
𝑬 𝒙 𝟏𝟎−𝟏𝟓
2
4.6366
2.7413
-9.9583
16.037
-9.1610
3
2.9526
1.3969
-4.9263
7.8601
-4.6076
5
3.6610
0.65637
-1.4115
2.0580
-1.2991
6
3.0485
1.3517
-4.8579
7.8854
-4.6908
7
2.5
0
0
0
0
8
2.9329
0.82661
-1.4640
1.5410
-0.68880
9
2.8386
1.1073
-2.9391
4.2052
-2.4217
10
3.2607
1.1910
Component
2.9732
-7.7377
9.4434
-4.2912
-9
11
2.5
-5.6533x10
12
2.5436
-0.027316
6.9448
-12
3.6325x10
-9.1995x10
-0.041903
0.49548
-4.2690
-4.0330
-16
-20
7.9526x10
-0.47955
Using the following heat capacity equation for the product gases:
∆ℎ𝑎 = �
1000
𝑡0
𝐿𝐶𝑝𝑎 𝑑𝑡 + �
𝑡𝑓𝑐
𝐻𝐶𝑝𝑎 𝑑𝑡
(6)
1000
where: a = component number
and the enthalpy equation (4) from above:
12
𝑄 = � 𝑣𝑎 ∆ℎ𝑎
𝑎=1
(7)
7
H
we can then conduct an iterative solution for tfc until Q agrees with -Δhcc.
𝑄 = 4139000 𝐽
𝑡𝑓𝑐 = 2264 °𝐾
which compares well with the reported value of 𝑡𝑓𝑟 = 2265 °𝐾.1
Now that the equations and variables have been validated, the additional inert gas (suppression
agent) is added using the following equation:
𝐼
𝑄 = � �𝑣𝑖 �
𝑡𝑒𝑥
𝑡0
𝑖=1
𝐶𝑝𝑖 𝑑𝑡� + 𝑣𝑔 �
𝑡𝑒𝑥
𝑡0
𝐶𝑝𝑔 𝑑𝑡
(8)
where again
𝑄 = −∆ℎ𝑐𝑐
and vg is the molar quantity of inert gas added per mol of heptane at the flame extinction limit
temperature.
The reported flame extinction limit temperature for heptane is1:
𝑡𝑒𝑥 = 1846 𝐾
Note that the actual tex under these exact conditions was not measured for the purpose of this
model.
Another factor that enters into the model at this point is room temperature. When this system
discharges, the room temperature is raised to ~60 °C. Therefore, combustion air and agent now
enter the reaction zone at this elevated temperature and therefore have slightly less heat
absorption capacity. This is taken into account by integrating the Cp terms for these components
from 333 K instead of standard conditions.
We now set t = t ex and use the following equations to calculate the new heat capacity for each
gas.
∆ℎ𝑎 = �
1000
𝑡0
𝐿𝐶𝑝𝑎 𝑑𝑡 + �
𝑡𝑒𝑥
𝐻𝐶𝑝𝑎 𝑑𝑡
(9)
1000
where: a = component numbers of heptane’s combustion products
8
∆ℎ𝑏 = �
1000
333
𝐿𝐶𝑝𝑏 𝑑𝑡 + �
𝑡𝑒𝑥
𝐻𝐶𝑝𝑏 𝑑𝑡
(10)
1000
where: b = component numbers of air and added agent
Our agent composition was described in Table 1. Using the mole fractions of each of the effluent
gases results in this final equation for Q:
𝑄 = � 𝑣𝑎 ∆ℎ𝑎 + � 𝑣𝑏 ∆ℎ𝑏
+ 𝑣𝑔 [0.620∆ℎ1 + 0.341∆ℎ3 + 0.0263∆ℎ2 + 0.0126∆ℎ8
+ 0.001∆ℎ6 ]
(11)
Now we conduct an iterative solution for vg until Q agrees with -Δhcr
𝑄 = 4139000 𝐽
𝑣𝐺 = 17.02𝑚𝑜𝑙
To calculate the gas fraction of agent in the room, we use the following equations:
𝑣𝑎𝑖𝑟 = 4.76(𝑛 + 𝑚/4)
(12)
this is 3.76 mol N2 plus 1.00 mol O2 for standard air
𝑋𝐺 =
𝑣𝐺
𝑣𝑎𝑖𝑟 + 𝑣𝐺
𝑋𝐺 = 0.245
(13)
which represents the fraction of our agent added to the room.
To calculate oxygen levels at extinction with this amount of agent:
𝑂2 = 20.9%(1 − 𝑋𝐺 ) 𝑂2 = 15.77%
(14)
𝑂2 = 20.9%(1 − 1.3𝑋𝐺 ) 𝑂2 = 14.24%
(15)
To calculate oxygen levels when an excess of agent is added to attain a safety factor of 1.3:
Test results from our 100 m3 National Fire Protection Association heptane pan fires show that
the OS-10 extinguishes at oxygen levels ranging from 16.8 to 17.1 percent. The difference in the
predicted oxygen level versus measured oxygen level must be accounted for.
9
The above model is based on inert gas heat capacity only. It is evident from visual observations
that the water component in our agent is in a partially condensed state. The condensed water has
not been accurately accounted for in the inert gas-based model.
Water mist fire suppression modeling involves several complex mechanisms. However, one of
the main mechanisms involves heat removal through the vaporization of the fine water droplets
by utilizing the latent heat of vaporization. This is the portion of the mechanism we now add to
this model to account for the differences between the pure inert gas model predictions and our
measured data.
To account for a portion of the water component of our agent being in the condensed phase, we
add an additional factor (fwc) to equation (11).
Where fwc is the condensed fraction of the water component, the equation for Q now becomes:
12
𝑄 = � 𝑣𝑎 ∆ℎ𝑎 + � 𝑣𝑏 ∆ℎ𝑏
𝑎=1
+ 𝑣𝑔 [0.620[(1 − 𝑓𝑤𝑐 )∆ℎ1 + 𝑓𝑤𝑐 (∆ℎ1 + 𝛥ℎ𝑣1 )] + 0.341∆ℎ3
+ 0.0263∆ℎ2 + 0.0126∆ℎ8 + 0.001∆ℎ6 ]
(16)
where the heat of vaporization of water is now included as:
∆ℎ𝑣1 = 41.1 𝑘𝐽/𝑚𝑜𝑙
If the equation is now solved for vg at various condensed water fractions fwc, the following set of
solutions for oxygen levels result as shown in Figure 2. The oxygen levels were calculated on a
gas only basis by using the following modified equation for XG
𝑋𝐺 =
�𝑣𝑔 (1 − 0.620𝑓𝑤𝑐 )�
𝑣𝑎𝑖𝑟 + �𝑣𝑔 (1 − 0.620𝑓𝑤𝑐 )�
(17)
In Figure 2, the green lines indicate the measured data. The modified model predicts that a
condensed water fraction of ~30 percent is required to obtain our measured oxygen levels. The
humidity levels in the room would confirm this. However, an instrument for rapid humidity
measurement has not been employed at this time, but is planned for future studies.
The OS-10 produces a combination of water vapor and very fine water particulates. During the
initial moments of gas generation (approximately 1second) the effluents of the gas generator pass
though a heat transfer bed that is at room temperature. The effluents are cooled below the
condensation temperature and a water fog is produced. As discharge continues, the temperature
of the cooling bed increases to the point where the water passing through does not condense and
remains a gas. This is witnessed in open air tests of the gas generator.
For the tests used in these studies, the cooling bed was sized to retain sufficient heat to limit the
room temperature to 60 °C. At 60 °C, the water in the air at the MEC is insufficient to achieve
saturation. However, for several minutes, the water that exits the gas generator in the liquid
phase (fog) persists and has been measured using a light meter. How much is in the condensed
10
phase has not been quantified but the prediction of 30% condensed phased is reasonable based
on the visual observations of fog during the discharge and subsequent light obscuration measured
(~23 percent over 1 m.)
Additional water mist mechanisms are also in play, such as oxygen depletion in the flame due to
expansion of the water from liquid to gas. These mechanisms have not been included in the
current model.
Figure 2. Calculated Room Oxygen Levels Versus Measured Data
for Various Condensed Fractions of Water
FIRE SUPPRESSION TESTING
Testing of the gas generator fire suppression system was conducted in a standard 100 m3
chamber with the UL2775 Class B heptane pan fire arrangement. Initial test protocol utilized the
Bruceton methodology to obtain a 50 percent extinguishing concentration of this agent. The
Bruceton method was used due to the inherent feature of gas generator sizing. The agent
concentration cannot be continuously adjusted; it can only be incrementally adjusted by
increasing or decreasing the number of generators deployed. The Bruceton method uses an
up/down philosophy where if a test is positive, the number of generators is decremented and
when a test is negative, the number of generators is incremented. This method is used until a
statistical probability is obtained around the extinguishing point.
A complicating factor is that there is no easy method of directly measuring the agent
concentration in the chamber due to the dynamic nature of the water vapor. The best method for
11
measuring agent concentration for this technology is chamber oxygen level. In order to achieve a
reliable oxygen measurement in the chamber, an O2 analyzer was purchased that had a built-in
water compensation ability. Most O2 analyzers are affected by high water content, which this
extinguishing agent creates. The manufacturers reported accuracy of this analyzer including
noise, linearity and repeatability is +/- 0.2% O2. Another factor that prohibits a reliable agent
concentration calculation from the gas generator effluents is that venting is required during
deployment. This venting allows an unknown portion of the discharged agent to exit the
chamber.
The test parameters for the gas generators are described as follows.
Each gas generator discharges in approximately 2.5 seconds. The system is initiated with a 1.2
amp signal for ~2 ms. This is generally provided by a sequencer developed by ATK to stage the
discharge of four gas generators, one every 2.5 seconds. Once the sequencer has received the
signal to discharge, the first gas generator is initiated immediately. The next gas generator is
discharged every 2.5 seconds until all gas generators in a four pack are discharged. Total
discharge time is 10 seconds for the four gas generators. Testing in the 100 m3 room was
conducted using three quad packs to reach the extinguishing concentration for Class B.
The results of the testing show that 12 gas generators are required for a statistically reliable
extinguishing concentration. Whenever the test was conducted with 11 generators, the fire was
not extinguished. Videos of an 11- and a 12-gas generator test are included in the final
presentation.
The oxygen measurements for two of the 12-generator Class B tests are shown in Figure 3. The
oxygen levels in the chamber ranged from ~16.8 to ~17.1 percent. This is in excellent agreement
with the model for the minimum extinguishing concentration (MEC) for this agent.
12
Figure 3. Measured Room Oxygen Levels for the MEC for Class B Heptane Fires
CONCLUSIONS
A model was developed following the successful approach also taken by J. Senecal.1 It is based
on the concept that when a fire suppressant is added to the gases surrounding a fire, the fire will
be extinguished when the heat absorbed by the gases present is equal to the heat produced by the
combustion process. The model predicts a combination of conditions that will extinguish a
heptane fire. The conditions include the volume of agent gas from the OS-10 gas generator, the
percent of the agent water in the condensed phase and the percent oxygen level.
Two full-scale tests in a 100 m3 volume demonstrated that the heptane fire is extinguished at
approximately 16.8 to 17.1 percent oxygen using the OS-10 gas generators. The model predicts
extinguishment at approximately 16.8 percent oxygen when 26 percent of the water is in the
room in the condensed phase and 17.1 percent oxygen when 32 percent of the water is in the
condensed phase. These data are in good agreement with each other and the amount of water in
the condensed phase is reasonable for the observed conditions.
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REFERENCES
1. Senecal, Joseph A., “Flame Extinguishing in the Cup-burner by Inert Gases”, Fire Safety
Journal, Volume 40, Issue 6, pp 579- 591, September 2005
2. Gordon, Sanford and McBride, Bonnie J., “Computer Program for Calculation of Complex
Chemical Equilibrium Compositions and Applications”, NASA Reference Publication 1311,
October 1994
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