CAFS compressed air foam system application

In the early 1980s, due to the scarcity of water in the surrounding area of ​​Texas and the extreme lack of water, the fire department developed CAFS (Compressed Air Foam System) to cope with this dilemma . In 1996 , CAFS began to enter China. At present, most fire stations in China are used as main vehicles.

CAFS is a kind of high energy storage foam. It contains a lot of high pressure air. In CAFS , water is still the most important part. It is mainly pre-mixed with foam, compressed air and water to fully refine and foam the aqueous foam solution. This greatly enhances the ability to penetrate into the interior of the combustor and adhere to the surface of the combustor.

Seven-bubble theory: A small drop of water turns into many bubbles, and the surface area of ​​the water expands by a factor of seven. This greatly increases the adhesion and penetration of the combustion material and improves the coverage and cooling. Seven bubble theory is also known as the CAFS design basis.

Problems with water in extinguishing fires:

1. Low fire extinguishing efficiency ( 15 - 20 %);

2. The scope of fire fighting is limited;

3. High renewability;

4. Large water loss;

5. Large water demand;

6. The delivery height is limited;

7. Fire trucks and hoses require high input.

CAFS advantages:

1. The fire extinguishing speed is fast, the re-ignitability is small, and the fire extinguishing efficiency is increased by 5 - 8 times;

2. Small water loss, easy to protect the scene and fire investigation and evidence collection;

3. The foam has a long holding time, good fireproof effect, good smoke coverage and barrier property ;

4. Loss along the way is small, the weight of the water belt is light, the firefighters consume less energy, and their mobility is stronger;

5. Under the same flow and pressure conditions, the range is farther and the vertical liquid supply can reach about 350 meters .

The compressed air foam can be divided into:

Wet foam, medium foam (medium wet foam and medium dry foam), dry foam.

The degree of wet and dry foam depends mainly on the ratio of water to air. Under normal circumstances, the air flow of the system is set (air flow is constant). When the flow of water increases, the foam becomes relatively wet, and vice versa. In addition, when the water flow is constant, the air flow increases the foam to dry, reducing the foam to become wet.

Dry foam moisture content: 8%-10% ;

Wet foam moisture content: 30%-50% .

Medium foam adjusts between the two as needed.

 

The specific application of CAFS :

1 Save A and B fires, such as tires, smoldering, and vehicle burning. Such fires produce a lot of smoke and heat when they are burned. Medium foam can be used with CAFS . The fire extinguishing efficiency is 5-8 times that of water .

2 Fire in special places such as museums, libraries, archives, precious ancient buildings, and laboratories. Such fires use water to extinguish fire, and buildings and interior valuables will be damaged. Water stains will even exceed the burning loss. The use of CAFS allows the use of dry foam to isolate flames, prevent the spread of fire, and use medium foam or dry foam to extinguish fires , thereby achieving the dual purpose of extinguishing and protecting buildings and precious objects.

3 Large-scale landfills or yard fires. The use of medium-foam coverage, long residence time, and low re-ignition property can be used to fight against the fire because the amount of water used is small and the amount of dirt removed is small, reducing secondary pollution.

4 Cover a lot of smoke and dust while extinguishing the fire. Since no direct impact on the water, and dry with medium foam or foam cover, reduce dust and water vapor, so characteristic of CAFS in 911 incidents, played a key role.

5 high-level fire.

( 1 ) Foam transport. The dry foam can be delivered to difficult heights when water is saved. The foam ratio is adjusted to between 0.5% and 0.7% . The dry foam is set because the dry foam contains less moisture and contains a large amount of air, which effectively reduces the weight of the water belt. Therefore, the dry foam can be transported to a sufficiently high height. .

( 2 ) Pressure control. When the compressed air foam system is working, the pump water outlet pressure is generally set at about 0.86 MPa , and the maximum working pressure is not easy to exceed 1 MPa , because the air pressure and water pressure in the CAFS system are automatically controlled by the pressure balance device in the system, so work here. Under pressure, a vertical distance of about 350 meters can be achieved . Therefore, there is no need for a higher outlet pressure of the water pump. If the water pump pressure is too high, due to the speed limit of the air compressor, it will affect the normal operation of the air compressor.

6 underground, tunnel fire fighting. Such fire CAFS uses medium-foam generators for medium-dry foam to quickly isolate air and drive out smoke. In times of suppression, the double-bubble generator should be used as much as possible. When using the double-bubble generator, the compressed air outlet valve should be closed because the generator adopts natural suction foaming method. If compressed air is added, it will affect Foam quality, and adjust the foam ratio to 0.5 to 1.0 according to fire conditions .

7 When the air compressor is working independently, it can be an independent source of emergency rescue equipment (such as rescue air cushions, etc.). It can also inject compressed air to disperse smoke and toxic gases. When using the air compressor independently, it should be noted that the pump must be operated to ensure the cooling of the air compressor.

This article is reproduced from the micro signal: burst rescue.