U-FUEL IONITION SUPPRESSION SYSTEM
(PATENT #5,562,162)

The U-Fuel Intornal Ignition Suppression System(IS²)is a result of an effort to logically study the factors necessary for ignition in an abooveground storage tank engulfed in fire and deternine the
most effective way to negate the potcndal for combustion．
Some fire jurlsdietions, concerned with the potential for ignition in aboveground tanks, require tanks be insulated to prevent the steel from reaching an average temperature of 260^。abeve ambient, or a maximum temperature of 400^。F, which is the ignition temperature of heptane, for a period of two hours. The problem with this approach is that it disregards the ASTME D 4814-92c composition of gasoline, the ignition requirements of gasoline and similar fuels, the impact of atmospheric pressure on ignition of fuels and the dynamics involved in heating gasoline in an aboveground tank involved in a fire.

GASOLIBE IS A MIXTURE OF LIQUID HYDROCARBONS WITH MULTIPLE BOILING POINTS.^1,2
A．ASTM D 4814-92c sets forth the distillation specifications for gasoline and provides five volatility clahses ranging from "A" for hot weather to "E" for cold weather．The "E" class is the most volatile, with a maximum 10％ distillation at 158。F. The maximum end point for all volatility classes is 437^。F.¹
B．For gasoline vapor to ignite there must be a supply of oxygen, in most cases air.³ The alr/vapor mixture must be proportioned accurately within the limits of flammabillty or ignition will not occur.^4.5 Ignition requires gasotine vapor be in the range of 1.4％ to 7.4% of the air.^6.7 Below 1.4% the mixture is too lean and will not ignite. Above 7.6% the mixture is too rich.³ Those who have tried to start a engine which is "flooded" have experienced a gasoline/air mixture abore 7.6%．too rich to ignite.
C．Aboveground tanks are now required to have vents that are normally closed, restricting the free flow of air into the tank.⁹ This restriction of air flow creates an environment in the tank that is difficult to ignite due to the higher molecular weight and density of gasoline vapors.^7,8,10
D．If an aboveground tank is involved in a fire, regardless of design. whether a single wall or a double wall, the gasoline jnside will absorb heat. Just as water can only be heated to its boiling point of 212^。F unlil it is boiled off, each hydrocarbon contained in gasoline can only be heated to its boiling point. As the temperature of gasoline increases to the boiling point of the first liquid fraction, the gasoline temperature stabilizes at that boiling point, say 122^。F, until that fraction is boiled off. Then the temperature of the gasoline increases to the boiling point of the next fraction where it stabilizes until that fraction is boiled off.^11,12 As long as heat is applied to the tank, this process continues to repeat itself until all the fractions are boiled off and there is no gasoline left in the tank at a maximum of 437^。F.^11,1 while this process is happening the vipors of the different fractions are being vented and burned due to the pressnre inside the tank. Any remaining gasoline vapors become more concentrated causing their ignition temperature to increase beyond the range of auto ignition.^4,13

E．In an atteanpt to create a scenario in which ignition could occur in aboveground tank due to rapid heat rise, the possibility of inducting air into a tank after a fire, during the cooling phase, was studied. Using Charles Law on the proportional expansion of gases with temperature.¹⁴ the percentage of air that can enter a tank when cooled was calculatcd：

Beginning Temperature	Ending Temperature	Percent Air Entering (After Cool Down)	Percent Difference
800 1,000 2,000	70 70 70	58 64 79	42 36 21

The worst possible condition is heating a tank to 2,000^。F，then cooling it to 70^。F, allowing 79 percent Of air to enter the tank on cool down. Danger occurs as air is unevely disbursed while entering the tank, creating pockets where the air/gasoline mixture is in the flammability range, auto ignitable due to intemal heat．

The U-Fuel Ignition Suppression System was developed to limit the potential for ignition. It works by. injecting an inert vapor into the tank, which duc to its chemical and diffusion properties, limits possible ignition of gasoline vapors. This process also decreases the heat inside the tank.

The inert material used by U-FueI expands 1.673 times its volume when it vaporizes. It only takes 7.2 gallons to protect a 12,000 gallon tank. As the liquid vaporizes, it absorbs a large amount of heat, 970.4 BTU/Ib.¹⁶

In actual tests of the U-Fuel Therrmo Tank with Ignition Suppression System. vapor Was rapidly generated and dispersed throughout the tank. causing a significant drop in all thermal couple sensors monitoring the intermal tank temperature.¹⁷

The Internal lgnition Suppression System vapor displaces gascs in the tank and limits possible ignition. IS² vapor is widely recognlzed as an effective inert gas extinguishing agent that will prevent the combustion of almost anything including hydrocarbons.^18,19

REFERENCES

l. 1993 Annual book of ASTM Standards, ASTM 4814-92c, Standard Specification for Automotive Spark-Ignition Engine Fuel, (Philadelphia: ASTM,1993). Vol 5.03, p 116, Tablel.
2．Ibid, para 3.1.2.
3．Warren E. Isman and Gne P. Carlson, Hazardous Materials, (New York：MacMillian Publishing, 1980), P 34.
4．Arthur E. Cote et al. Fire Protection Handbook (Batterymarch Park: National Fire Protecion Association(NFPA), 1991), p 1-45, Chemistry and Physics of Fire.
5．Isman and Carlson, p 35.
6．Coward, H.F. and Jones, G.W. "Limits of Flammability of Gases and Vapors" Bulletin 503, 1952, Bureau of Mines, U.S. Department of Interior, Table 45.
7. Insman and Carlson, p 36, Table 2-3.
8．Ibid. p 36.
9．NFPA-30, Flammable and Combustible Liquids Code, 1993 ED. (Batterymarch Park：NFPA,
1993), p 15, para 2-3, 5.6 and p 18, para 2-4.5.).
10．Jbid, p 55, Table B-2.
11．James E.Brady and Joha R.Holum, Fundamentals of Chemistry, (New York：John Wiley＆Sons, 1988), p 368＆1,015.
12．ASIM D 4814-92c, p 134.
13．Brady and Holum p 315.
14. Ibid., p 320.
15．RJ. Dossat, Principles of Refrigeration. (New York：John Wiley＆Sons, Inc. 1961),p 25, para 3-4.
16．Ibid., p 31.
17．Southwest Research Instltute Project 01-5330-604, May 1994.