Application of Fluoroprotein Foam Fire Extinguishing Agent in Fighting Oil Tank Fire

【Abstract】Fluoroprotein foam fire extinguishing agent is an important fire extinguishing agent for oil tank fires, and has obvious advantages over protein foam fire extinguishing agent. In the underwater spraying, attention should be paid to the relationship between the amount of oil entrained and the foam expansion multiple, the speed of foam entering the oil and the thickness of the oil; in the oil surface spraying, the quality of foam formation and the efficiency of coverage should be guaranteed, and attention should be paid to the combination with dry powder to enhance the fire extinguishing effect.

With the continuous development of my country's economic construction and the deepening of industrialization, the demand for "industrial blood" - oil and its products has continued to grow, and various oil storage areas have been continuously established and the storage volume has continued to increase. For this kind of flammable and explosive liquid, various fire hazard factors are both numerous and very complex. Once an explosion occurs, a large-scale fire will often form, and the fire will also be extremely fierce. Therefore, extinguishing oil fires has become a difficult problem facing the majority of firefighters. This article puts forward some personal views on the application technology of fluoroprotein foam fire extinguishing agent in extinguishing oil tank fires.

1. Characteristics of fluoroprotein foam liquid

To extinguish oil tank fires, a large amount of fire fighting technology and equipment are often required, and a large amount of manpower and material resources need to be invested. As far as fire extinguishing agents are concerned, in addition to water, foam fire extinguishing agents are also indispensable "ammunition". In many cases of fighting oil tank fires in my country, fluoroprotein foam fire extinguishing agents have played a very important role.

Fluoroprotein foam fire extinguishing agent is a foam fire extinguishing agent developed in the 1960s to overcome the shortcomings of protein foam fire extinguishing agent. It is made of protein foam fire extinguishing agent as the base material and an appropriate amount of "6201" prefabricated liquid added. (Note: "6201" prefabricated liquid is also called FCS solution, which is an aqueous solution prepared by "6201" fluorocarbon surfactant, isopropyl alcohol and water in a mass ratio of 3:3:4) 6% fluoroprotein foam fire extinguishing agent contains 1% "6201" prefabricated liquid, and 3% fluoroprotein foam fire extinguishing agent contains 2% "6201" prefabricated liquid.

The fire extinguishing principle of fluoroprotein foam fire extinguishing agent is basically the same as that of protein foam fire extinguishing agent, but due to the effect of fluorocarbon surfactant, its fire extinguishing performance is greatly improved. Compared with protein foam fire extinguishing agent, fluoroprotein foam fire extinguishing agent has obvious characteristics: first, the surface tension and interfacial tension are significantly reduced; second, the foam has good flowability and fast fire extinguishing speed; third, fluoroprotein foam has strong ability to resist oil pollution and can extinguish large oil tank fires by underwater spraying; fourth, it can be used in combination with dry powder. Therefore, fluoroprotein foam fire extinguishing agent is widely used in the fire fighting of large oil storage tanks.

2. Application of fluoroprotein foam fire extinguishing agent in underwater spraying

Oil storage tanks are generally tall and have a large oil storage capacity. After the explosion and fire, the fire is fierce, the temperature is high, the radiant heat is strong, and it is easy to spread and expand. There may even be continuous explosions, boiling and splashing, and the tank body is deformed and collapsed. It is difficult for personnel, vehicles and equipment to approach the battle, and it is extremely difficult and dangerous to extinguish the fire. In this case, the foam fire extinguishing system attached to the oil tank plays a vital role in controlling the fire in the initial stage and preventing it from spreading and expanding. Due to the high combustion temperature of oil tank fire, the liquid spray fire extinguishing system is vulnerable to damage, so the underwater foam spray fire extinguishing system is safer and more reliable. Since the underwater foam spray fire extinguishing system sprays the foam directly into the oil from the bottom of the tank through a pipe, floats up under the buoyancy of the oil, and covers the burning oil surface for fire extinguishing, the underwater spray has a strong selectivity for the foam liquid, and fluoroprotein foam liquid is generally used. When spraying fluoroprotein foam underwater, the main problem to be solved is how to prevent the foam from entraining too much oil to become a combustible foam and lose its fire extinguishing ability. Experiments have shown that when spraying foam underwater, the amount of oil entrained is mainly related to the foam expansion multiple, the speed at which the foam enters the oil, and the thickness of the oil.

1. Reasonably design the foam expansion multiple of the foam. The relationship between the foam expansion multiple and the foam oil content obtained by cold spraying a gasoline tank with a diameter of 2.7 meters and an oil layer thickness of 9 meters is shown in the figure.

Fluoroprotein foam has both hydrophobicity and strong oleophobicity because the fluorocarbon chain in the fluorocarbon surfactant molecule can form a water film at the junction of foam and oil, and can also wrap oil droplets in the foam to prevent oil evaporation and reduce the flammability of oil-containing foam. According to measurements, the gasoline content in fluoroprotein foam can only burn freely when it is above 17%. In order to control the oil content of the foam within the non-combustible concentration and consider its comprehensive fire extinguishing effect, the foam expansion multiple should be controlled at about 3 times. Therefore, when spraying fluoroprotein foam underwater to extinguish gasoline tank fires, a special high back pressure foam generator must be used, and the working pressure must reach 7×105Pa.

2. Reasonably control the speed at which foam enters the oil product. The speed at which foam enters the oil product is an important technical parameter. From the test, it is known that as the speed at which foam enters the oil product increases, the oil content in the foam also increases accordingly. This is because, as the flow rate increases, the agitation of the foam and the oil product and the turbulence formed by the oil product in the oil tank also increase, resulting in an increase in the oil content of the foam. In order to reduce the oil content in the foam and ensure the fire extinguishing effect, it is necessary to limit the speed at which the foam enters the oil. Tests show that the entry speed of fluoroprotein foam with a foaming multiple of 3 times for Class A and B flammable liquids such as gasoline and low flash point crude oil cannot exceed 3m/s; for Class C flammable liquids with high flash point or low volatility, such as kerosene and diesel, the foam entry speed can be slightly higher, but generally cannot exceed 6m/s. In addition, when spraying underwater, there are certain restrictions on the thickness of the oil in the storage tank. For example, the thickness of the oil in the gasoline tank generally does not exceed 9 meters.

3. Application of fluoroprotein foam fire extinguishing agent in oil surface spraying

In the fire fighting of oil tanks, in addition to using the fixed fire extinguishing facilities attached to the oil tanks, the operation of fire fighting technical equipment such as foam guns, cannons, hook pipes, etc. for fire fighting is the main aspect of the entire combat operation. There are two main aspects of the technology of spraying oil surface with fluoroprotein foam fire extinguishing agent: one is to ensure the quality of foam formation, that is, the water and foam liquid are mixed well and the foaming multiple is high. Specifically, the foaming multiple is not less than 6 times of the mixed liquid; the second is to ensure the efficiency of foam coverage, that is, the foam can be sprayed on the oil surface as much as possible without causing artificial mechanical damage and waste to the foam.

In terms of ensuring the quality of foam formation, it mainly involves the following links:

1. The adjustment of various pointers and valves should be coordinated and consistent. When using foam guns, cannons, and hook tubes to spray foam, the position of the pointer on the foam mixer should be consistent with the model of the foam gun, cannon, and hook tube used. For example, when using a 25L foam tube gun, the position of the pointer on the foam mixer should be adjusted to 25 (PH4); if using a 50L, the position of the pointer should also be adjusted to 50 (PH8), and so on. Do not mistakenly believe that the pointer on the foam mixer is used to adjust the foam generation multiple. When the foam is not formed well, the pointer is adjusted randomly, and the result is worse and worse. The valve at the pump outlet and the closing and opening valves on the foam gun should be completely opened. In addition, pay attention to opening the top cover of the foam tank to let air in, so as to avoid the formation of a vacuum in the foam tank and the inability to transport the foam liquid out.

2. Ensure the working pressure of various guns, cannons, and hooks so that the mixed liquid and air can be fully mixed. The air mechanical foam currently used by the fire brigade is mainly formed by the mixed liquid and air being fully mixed under the action of the machine. In order to fully mix the mixed liquid and air, there must be sufficient mechanical action, and various guns, cannons, and hooks must have sufficient inlet working pressure. According to the needs of the inlet working pressure of various foam guns, cannons, and hooks, the working pressure of the pump should be adjusted so that the mixed liquid and air can be fully mixed.

In terms of ensuring the efficiency of foam coverage, there are mainly the following issues that need to be paid attention to:

1. Minimize mechanical impact as much as possible. Due to strong mechanical impact, a large amount of foam will burst, thereby destroying the foam. Therefore, when spraying foam, it should be sprayed directly on the tank wall or other objects, not on the oil surface. It should be sprayed along the tank wall and close to the oil surface as much as possible, so as to minimize the damage caused by mechanical action.

2. Avoid high temperature damage as much as possible. Because high temperature will have a certain destructive effect on foam, when spraying foam, try to prevent the foam from flowing too much through the high-temperature tank wall, and pay attention to avoid flames.

3. Try to speed up the flow rate. The use of foam to extinguish oil fires mainly relies on the flow of the foam itself to cover, so as to achieve the fire extinguishing effect. In order to speed up the flow of foam, the spray gun can be waved appropriately to make the foam fire extinguishing effect better.

A large number of fire extinguishing tests have shown that the reasonable selection of two or more fire extinguishing agents for joint fire extinguishing can combine the advantages of each fire extinguishing agent, which is better than using one fire extinguishing agent alone. The technology of using fluoroprotein foam fire extinguishing agent and dry powder fire extinguishing agent to extinguish oil tank fires is a fast, reliable and efficient fire extinguishing method for extinguishing large-scale oil fires, which can minimize fire losses and obtain the best social and economic benefits. The fire extinguishing technology of fluoroprotein foam combined with dry powder can not only give full play to the advantages of the thoroughness of foam fire extinguishing and the rapidity of dry powder fire extinguishing, but also overcome the defects of the slowness of foam fire extinguishing and the easy re-ignition of dry powder fire extinguishing, and achieve better fire extinguishing effect. This is because the surface tension of fluoroprotein foam is lower than that of fuel, which can not only resist the rupture caused by fuel, but also resist the pollution and damage of dry powder, so it can achieve the best fire extinguishing effect.

Of course, when fluoroprotein foam is used in combination with dry powder, only by choosing a better combination method can the advantages of each fire extinguishing agent be brought into play and a better fire extinguishing effect be achieved. When foam and dry powder are sprayed at the same time, the fire extinguishing effect is not ideal, which may be caused by the mutual interference between foam and dry powder when passing through the flame zone. When a certain fire extinguishing agent is used for a period of time and then sprayed at the same time, the effect is better than using fluoroprotein foam alone. The test shows that when the foam is sprayed for 5 seconds first, the foam and dry powder are sprayed at the same time when the fire is basically controlled by half, the best effect can be achieved. This combination method achieves the purpose of using the least amount of fire extinguishing agent to extinguish the fire.