Cryogenic Suppression of Liquid Pool Fires and Wooden Crib Fires
Yiannis A. Levendis
College of Engineering Distinguished Professor
Department of Mechanical and Industrial Engineering
334 SN, Northeastern University
360 Huntington Avenue
Boston, MA 02115, USA
Tel : 617-373-3806
e-mail: y.levendis@neu.edu
Michael A. Delichatsios
Michael A. Delichatsios, Professor
Director of Fire Safety Engineering Research and Technology Centre
Chair and Head of Fire Dynamics and Materials Lab (FML)
University of Ulster, Northern Ireland, UK
Tel: +44 (0) 28 9036 8058
Fax: +44 (0) 28 9036 8726
e-mail: M.Delichatsios@ulster.ac.uk
Abstract
Results on fire suppression by direct application of liquid nitrogen are presented in this manuscript. This
technique targets challenging fires, such as burning hazardous chemicals and fuels, in which cases their
expedient suppression or extinction is paramount to prevent explosions, avoid prolonged release of
toxic fumes and avert environmental catastrophes. Liquid nitrogen is an environmentally-benign fire
suppression agent which does not cause property damage or groundwater contamination. Application
of this cryogen onto a hot pyrolyzing/burning surface induces abrupt vaporization and associated
expansion. The pyrolyzing gases are inerted, the surface is cooled, thus its pyrolysis rate is reduced, air is
separated from the fuel, and the fire extinguishes. This technique was successfully demonstrated in
small-scale experiments of two distinct configurations: (a) pool fires of hydrocarbon fuels and (b)
wooden crib fires.
KEYWORDS: fire extinction, fire suppression, liquid pool fires, wooden crib fires, liquid nitrogen cryogen
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Introduction
Fire is one of the leading causes of loss of property and life around the world. There are
inadequacies with current techniques for extinction of fires in chemical plants, fuel storage
installations, warehouses, etc. Many such fires are difficult to control in a timely fashion and are
often threatening to their surroundings. Some fires have been reported to burn for long times
with dire environmental consequences. Thus, in cases where currently-used extinction agents
and methods are only partially-effective and often problematic, new agents and techniques
may find applications. It is often the case that use of water or chemical fire extinguishers cause
unwanted side effects, such as extensive “water damage”, air pollution, or underground water
contamination.
Hence, along with the continuous development of fire prevention
methodologies and early detection technologies, new fire extinguishing agents and techniques
are also needed. This manuscript discusses the benefits of direct application of liquid nitrogen
in fire suppression and extinguishment.
This cryogen may be applied to many types of fires, both open and closed [1-4]. Certainly, there
are some obvious limitations, i.e., the cryogen should be applied to locations at the absence of
living beings, since it is both a freezing and an asphyxiating agent, especially in closed
compartments. The cryogen should also be handled carefully since skin contact may result in
frostbite. Otherwise, mature technologies exist and installations are in place for the production,
handling, distribution and storage of this cryogen in a large number of locations. The cryogen is
safe for the environment and it is relatively inexpensive (in the order of $1 per gallon). Liquid
nitrogen may provide firefighters with an expertise method for fire extinction in demanding
situations. Various technologies are envisioned for delivering liquid nitrogen to fires, including
delivery by insulated trucks, hoses and unmanned vehicles [5]. Application of liquid nitrogen
may be used alone or in conjunction with other conventional methods, such as those using
water in the form of sprinklers or direct water hose impingement.
Experimental Results and Discussion
This manuscript describes experiments conducted with liquid fuel pool fires and with wooden
crib fires. The experiments were conducted at Northeastern University (NU), at CSIRO's
laboratory in Sydney, Australia; and at the laboratories of Factory Mutual (FM) in Norwood,
Massachussets, USA.
(i) Two-dimensional fuel pool fires – manual application
The investigation at CSIRO involved pool fires of two different fuels (propanol and diesel oil)
with dimensions of 1 m2, 2.5 cm deep. The pan containing the fuel was placed inside a bigger
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pan containing water. The propanol flames were of bright orange color, whereas those of diesel
oil were darker orange and very sooty. Small quantities of gasoline were added to facilitate the
ignition of diesel oil. Half-litter quantities of the cryogen were manually poured from a small
height (15 cm above the fire), either inside the pan containing the burning fuel or outside the
pan, close to its periphery. Direct application of the cryogen inside the pan (at one corner or
along a side) was remarkably successful in suppressing and extinguishing both the propanol and
the diesel oil fires. As soon as the cryogen was poured at one corner of the fuel pool it flashvaporized, its vapors spread over the entire pool, and extinguished the fire expediently (in the
order of a few seconds), see Fig. 1. The cloud of nitrogen then spread over the outside water
pool and, subsequently, over the laboratory floor, covering an area of approximately 3 meters
in diameter. The height of the cloud was only 15-20 cm, because of gravity. The coverage of
that area by the nitrogen vapors, upon extinguishment of the flame, lasted for a few minutes.
This technique was also successful at the presence of wind, generated by a fan, the cryogen
been poured at a corner of the fuel pool upstream of the flame. Thus, this experimental series
revealed that flames of 1 square meter can be successfully and expediently extinguished with
half-liter of cryogen poured at one corner of the flame. It should be mentioned here that the
gentle pouring of the cryogen, as well as the existence of the pan’s side walls confined the
fuel inside the pan and prevented, or at least minimized spillage outside, i.e., in the water
pool.
Application of the cryogen outside the burning fuel pan was successful in suppressing the fire,
but not in completely extinguishing it, with one notable exception. Extinguishment was
accomplished when the cryogen was poured outside of the fuel pool, at the presence of a
constant speed and constant direction wind. In that case, the cryogen was poured upstream of
the fire. The cryogen vapors were then effectively carried by the wind over the fire, where they
mixed with and inerted the burning gases. Otherwise, when the cryogen was poured outside of
the fuel pool, i.e., in regions much cooler than the flame such as the pool of water or the
surrounding floor, it experienced slower vaporization/expansion rates. Liquid nitrogen was
often seen slowly boiling in the pool of water, creating chunks of ice in the process. Nitrogen
vapors were sucked in by the flame, often in a swirling motion and gradually suppressed the
flame for a while (1-2 min) until the nitrogen vapors dispersed; subsequently the flame
rejuvenated.
(i) Two-dimensional fuel pool fires – application by hose
As large-scale fire extinction by application of liquid nitrogen cannot be done manually, a
handling and delivery system is needed. A proposed system would consist primarily of a
transport vehicle, a pumping system, a phase separator and an insulated delivery hose
terminated by the custom nozzle. Most of the components are commercially available, see Fig.
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2, but to date they have not been combined into a mobile fire extinction system. The feasibility
of this concept was first shown at NU with a home-made deliver system [7]. This system
consisted of a pressure vessel wrapped in foam insulation with an inlet valve on top and a
manual vent on its side. The outlet was located at the bottom of the tank and was controlled by
a manual ball valve. This valve allowed liquid nitrogen to flow in an insulated copper pipe that
was adjusted to a 25º launch angle. The vessel was filled with liquid nitrogen with vents open to
allow for the gaseous expansion, taking place as the tank cooled down. Once the tank was
filled, the vents were closed and pressure was allowed to build. Although the conversion of
nitrogen from liquid to gas built sufficient pressure in the tank for the tests, a compressed air
line was connected in order to maintain a steady pressure throughout the emptying of the tank.
The system also incorporated two separate pressure relief valves and a pressure gauge to
ensure safe operation.
Initial tests were performed using water to check for leaks and to determine expected spray
patterns. From preliminary findings, a target of 7 m was decided upon for the delivery of liquid
nitrogen. A 30 cm diameter pan, containing a 1 cm layer of isopropyl alcohol, was placed at the
target zone and was ignited. Results were positive with the cryogen extinguishing the fire in
seconds, and with its vapors blanketing the pan for a while (minutes), see Fig. 3. The test was
performed several times with repeatable results. The test results have validated the idea of
projecting a stream of liquid nitrogen from a hose and nozzle in order to extinguish a Class B
fire.
(ii) Three-dimensional wood crib fires:
Two different tests were performed with standard wood cribs (crates) at FM. The only
difference was in the pre-burn time, i.e., for how long was the crib allowed to burn before the
cryogen was applied. In these tests a 30×30×30 cm (1’×1’×1’) wood crib was placed on a
30×30×7.5 cm high inner pan centered in another 75×75×5 cm high outer pan; 200 ml of
heptane was evenly distributed in the inner pan for ignition; the crib consisted of thirty two
3.25×3.25×30 cm long pine sticks stacked up in 8 layers (4 sticks per layer); the crib weighed
about 7 kg. The cryogen was poured from a height of 77 cm above the wood crib.
In the first test the fire was ignited and the crib was allowed to burn for 2 min. One litter of
liquid nitrogen was slowly (~5 s) distributed above the wood crib. The fire was suppressed and
extinguished instantly. No embers were observed.
In the second test the fire was ignited and the crib was allowed to burn for a longer period, this
time 3 min. The extra time (1 min) allowed this fire to be deeper-seated in the wood structure,
which made it more difficult to extinguish. This time, a quantity of one liter of liquid nitrogen
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was poured manually in the larger pan, 30 cm diagonally from a corner of the wood crib. The
flame in the lower 1/4 section of the crib was suppressed after this application of liquid
nitrogen, see Fig. 4a. Two minutes later the fire re-grew to full strength. Then a second liter of
liquid nitrogen was slowly (~5 s) distributed above the crib, see Fig. 4b. The flame was totally
suppressed but the embers remained, see Figs 4c and 4d. The fire re-established a few minutes
later and a third liter of the cryogen was manually poured to the top of the crib. The flame was
again readily suppressed, but the embers still remained. The same result was obtained for
subsequent manual applications of liquid nitrogen. Each time the fire slowly transitioned from
smoldering to flaming, it was never completely extinguished. Smoldering is defined as a nonflaming, self sustaining, propagating process, deriving its principal heat from heterogeneous
fuel oxidation [8,9]. The embers were eventually extinguished by spraying water when the fire
was smoldering. A subsequent test showed that much smaller quantities of water were needed
to extinguish the crib fire during its smoldering period than during its flaming period.
Conclusions
An experimental study was conducted to assess the fire extinction effectiveness of liquid
nitrogen. The cryogen was directly applied to fires as a liquid. Both two-dimensional liquid-fuel
confined pool fires and three-dimensional wood crib fires were examined.
Liquid pool fire experiments showed that as soon as small quantities of liquid nitrogen reach a
burning surface they change phase and expand, forming a cylindrical cloud spreading over and
near the surface. The following major fire extinction mechanisms apply simultaneously: (i)
surface cooling because of the very low temperature of this cryogen (77 K) and effective heat
transfer by boiling; (ii) inerting of the surrounding atmosphere, which starves the fire from
oxygen; (iii) rapid expansion followed by gravity spread that results in blanketing of the surface
with a cloud of condensed water, and possibly some fuel, vapors. This cloud also blocks
radiation from adjacent flames to the pyrolyzing surface. As the temperature of liquid nitrogen
is very low, and the expansion at high temperatures is very large, these sequential processes
are exceedingly fast. Systematic experiments showed that there is a minimum amount of
cryogen needed for a given fire size, there is a maximum height from which the cryogen may be
delivered, and that a good distribution of the cryogen over the fire may not be always
necessary. In deep pool fires abrupt dumping of cryogen in bulk may induce splashing/spilling
of burning fuel to a larger area. The specific gravity of the liquid fuel appears to be an
important parameter. The existence of constant direction wind may be used to an advantage if
the cryogen is applied upstream of the fire. Then the wind may carry and spread the nitrogen
vapors over the fire and blanket it. In summary, whereas this technique appeared to be
exceptionally effective in the extinction of certain fires, issues still remain to be resolved to
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determine the effects of the characteristics fuel, the pool depth the mode of application, the
burning liquid density, etc.
The experiments involving the wood cribs (crates) revealed that porous solid materials pose
additional challenges. If such materials are left to burn for a sufficiently long period of time,
fires become deeply-seated in the pores and crevices of the solids. Whereas liquid nitrogen
applications suppress the flaming combustion of solids, smoldering combustion in the pores
may take place and the embers are likely to reignite. Application of water is still needed to
extinguish smoldering combustion, albeit in much smaller quantities than had its application
occurred during the flaming combustion of the same solids. Smaller quantities of water are
easier to procure and minimize “water damage”.
Care must be exercised to apply liquid nitrogen in well ventilated areas or at the absence of
living beings. Liquid nitrogen has certain advantages, as it completely vaporizes and dissipates
in the atmosphere leaving no residue, no additional damage of materials (such as “waterdamage”), no contamination of the ground waters, no atmospheric pollution.
Acknowledgements
Technical assistance is acknowledged from Drs. Hong-Zheng Yu and Hsiang-Cheng Kung at
Factory Mutual Research in Norwood, Massachusetts, as well as Justin Leonard, Fire Science
and Technology Laboratory, CSIRO, North Ryde, NSW, Australia. The experimental results
shown in Fig. 3 were obtained by the Northeastern University students Christopher Breen, Ruy
Ferreira, Sam Hinckley, David Walazek and Blake Wilcox during their “capstone” design course
[7].
References
[1] Y. A. Levendis, M.A. Delichatsios, J. Leonard, H-Z Yu, H-C Kung, “Extinction of Fires by Direct
Dumping of Liquid Nitrogen.” Proceedings of the 9th International Fire Science & Engineering
Conference (InterFlam 2001), pp. 279-290, Edinburgh, Scotland, September 17-19, 2001.
[2] Y.A. Levendis, “Liquid Nitrogen as a Fire Extinction Agent.” Proceedings of the First Joint
Meeting of the Italian and Greek Sections of the Combustion Institute, Corfu, Greece, June 1720, 2004.
[3] Y.A. Levendis, M.A. Delichatsios, “Pool Fire Extinction by Direct Application of Liquid
Nitrogen.” Proceedings of the 5th US Combustion Meeting of the Combustion Institute, San
Diego, March 25-28, 2007.
6
[4] Y. A. Levendis, M.A. Delichatsios, “Liquid Assets” Yiannis A. Levendis and Michel A.
Delichatsios. Fire Prevention Fire Engineers Journal of the British Fire Protection Association.
September 2007, pp. 54-56.
[5] Y. A. Levendis, A. Ergut and M.A. Delichatsios “Cryogenic Extinguishment of Liquid Pool
Fires.” AIChE Journal of Process Safety Progress, 29, 79-86, 2010.
[6] Y. A. Levendis and M.A. Delichatsios “Cryogenic Extinguishment of Liquid Pool Fires.” AIChE
Journal of Process Safety Progress, accepted for publication 2010.
[7] C. Breen, Breen, R. Ferreira, S. Hinckley, D. Walazek, LN2 Cryogenic Fire Extinction, technical
design report, College of Engineering, Northeastern University, Boston 2005.
[8] A.P. Aldushin, A. Bayliss, B.J. Matkowsky, On the Transition from Smoldering to Flaming.
Combustion and Flame, 154, 579-606, 2006.
[9] T.J. Ohlemiller, Progress in Engineering Combustion Science 11, 277, 1985.
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Figures
Application of the cryogen
Figure 1. Photographic sequence from an experiment where a 1 m2 diesel oil pool fire was manually
extinguished by ½ liter of liquid nitrogen, applied to its upper left corner, see arrow.
b
c
Figure 2. Photographs of (a) a commercial liquid nitrogen truck, (b) cryogenic pump and (c) vacuuminsulated hose.
Figure 3. Photographs of fire extinction of a small (30 cm in diameter) alcohol-pool fire, set at a distance of
7 meters away from a liquid nitrogen hose/nozzle that sprayed the cryogen. Liquid nitrogen “rained” on the
liquid pool and the fire was extinguished in a few seconds [6].
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a aa
b
c
d
Figure 4. A 30×30×30 cm (1’×1’×1’) wood crib was placed on a 30×30×7.5 cm high inner pan centered in another
75×75×5 cm outer high pan; 200 ml of heptane was evenly distributed in the inner pan for ignition The fire was
ignited and the crib was allowed to burn for 3 min. (a) A quantity of one liter of liquid nitrogen was poured
manually in the larger pan, 30 cm diagonally from a corner of the wood crib. The flame in the lower 1/4
section of the crib was suppressed after this application of liquid nitrogen. (b) Two minutes later the fire regrew to full strength. Then a second liter of liquid nitrogen was slowly (~5 s) distributed above the crib. (c)
the flame was totally suppressed but (d) the embers remained. The flame was later re-established.
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