As a new alternative technology, the water mist automatic fire extinguishing system has shown very superior characteristics and has attracted extensive attention from the international fire protection community.
The water mist fire extinguishing system refers to the fire extinguishing system used to extinguish class A, B, and electrical fires. The water mist fire extinguishing system uses water as the fire extinguishing medium, and uses the fine water mist nozzle to work under a specific pressure (usually the nozzle pressure is 10MPa) is a fixed fire extinguishing system that decomposes the water flow into small water droplets for fire extinguishing. It has the characteristics of economy and a wide application range.
Definition of water mist fire extinguishing system
Fine water mist: Under the minimum design working pressure, the water mist droplets with a diameter of Dv0.50≤200μm and Dv0.99≤400μm are sprayed out from the nozzle and formed on a plane 1m downward from the axis of the nozzle.
Classification of water mist fire extinguishing system
- Classified by water supply method:
① Bottle group type water mist fire extinguishing device;
②Pump type water mist fire extinguishing device;
③Other water supply methods: fine water mist fire extinguishing device. - Classified by flow medium type:
①Single-fluid water mist fire extinguishing device;
② Two-fluid water mist fire extinguishing device. - Classified according to the working pressure of the device:
①High pressure water mist fire extinguishing device (P≥3.50MPa);
②Medium pressure water mist fire extinguishing device (1.20MPa≤P<3.50MPa);
③Low pressure water mist fire extinguishing device (P<1.20MPa).
Note: P is the pressure of the flowing medium in the distribution pipe network. - Classified according to the type of fine water mist nozzle used:
①Closed water mist fire extinguishing device;
② Open water mist fire extinguishing device.
Technical parameters of water mist fire extinguishing system
- Working temperature:
The working temperature range of the fine water mist fire extinguishing device (hereinafter referred to as the device) is 4°C~50°C. - Working pressure:
①The manufacturer shall specify and indicate the maximum working pressure and storage pressure of the device and the allowable working pressure range of the fine water mist nozzle.
②The gas storage pressure of the bottle group device and the maximum working pressure of the device shall meet the requirements in the table below (when the storage gas is nitrogen).
| Gas storage pressure/MPa | Max working pressure(@50℃)/MPa |
| 15 | 17.2 |
| 20 | 23.2 |
③The minimum working pressure of the single-fluid fine water mist nozzle should be selected from the series of 1.2MPa, 1.5MPa, 2.0MPa, 3.0MPa, 3.5MPa, 4.0MPa, 5.0MPa, 6.0MPa, 8.0MPa, and 10.0MPa.
- Flow coefficient:
The nominal flow coefficient of the fine water mist nozzle should be selected from the series of 0.3, 0.5, 0.7, 0.9, 1.0, 1.2, 1.5, 1.7, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5.
Water mist system fire extinguishing requirements
- Fire extinguishing requirements for open water mist nozzles
Carry out the fire extinguishing test for Class B fire according to the prescribed method. The local application of a fine water mist nozzle should extinguish the fire within 5 minutes after the spraying starts, and there should be fuel remaining in the oil pan after the test.
Carry out the fire extinguishing test of Class B fire according to the specified method. The fully submerged fine water mist nozzle should extinguish the fire within 15 minutes after the start of spraying. The average temperature measured after spraying for 3 minutes should be less than 100 ° C. After the test, there should be fuel remaining in the oil pan. - Closed water mist nozzle fire extinguishing requirements
The corner fire extinguishing test shall be carried out according to the prescribed method, and the following requirements shall be met:
① The water mist nozzle located directly above the door should not be activated;
②The highest temperature at the ceiling directly above the igniter is less than or equal to 265°C;
③The highest temperature at 76mm below the ceiling directly above the igniter is less than or equal to 315°C.
The sofa fire extinguishing test shall be carried out according to the prescribed method, and the following requirements shall be met:
① The number of activated water mist nozzles is less than or equal to 5;
②The volume or weight loss of the combustibles is less than or equal to 50%;
③The temperature of the ceiling directly above the igniter is not greater than 260°C;
④ The highest temperature at the place 76mm below the ceiling directly above the igniter is not greater than 315°C.
Fire Extinguishing Mechanism of High-Pressure Water Mist Fire Extinguishing System
- High-efficiency cooling effect: Since the droplet diameter of the fine water mist is very small, the diameter of the mist particle in the ordinary water mist system is 10-100 μm. During the process of vaporization, it absorbs a large amount of heat from the surface of the burning object or the fire area. Based on the latent heat of evaporation of water at 100°C as 2257kJ/kg, the heat absorption power of water mist sprayed by each nozzle (water spray speed 0.133L/s) is about 300KW. Experiments have shown that the smaller the diameter, the greater the heat absorption per unit area of the water mist, the faster the droplet velocity, the smaller the diameter, and the higher the heat transfer rate.
- Suffocation effect: After the fine water mist is sprayed into the fire site, it evaporates rapidly to form steam, and the volume expands sharply by 1700-5800 times, reducing the oxygen volume fraction and forming a barrier around the burning material to prevent the inhalation of fresh air. With the rapid vaporization of water, the water vapor content will increase rapidly, and at the same time, when the oxygen content decreases to 16% to 18% in the space around the fire source, the flame will be suffocated. In addition, the fog droplets in the non-combustion area outside the fire site will not vaporize, the oxygen content in the air will not change, and it will not endanger the lives of personnel.
- Block radiant heat: After the high-pressure water mist is sprayed into the fire site, the steam formed by evaporation quickly covers the combustion, flame, and smoke, and has an excellent ability to block the radiant heat of the flame, which can effectively inhibit the radiant heat from igniting the surrounding area. Other items to achieve the effect of preventing the spread of flames. The attenuation effect of water mist on radiation can also be used to protect the lives of firefighters. Dilution, emulsification, and wetting: the droplets with large particles and large impulse will impact the surface of the burning material so that the burning material can be soaked, and the further generation of solid volatile combustible gas can be prevented, to achieve the purpose of extinguishing the fire and preventing the spread of the fire. In addition, the high-pressure water mist also has the functions of washing smoke and exhaust gas, emulsifying and diluting liquids, etc.
Features of high-pressure water mist fire extinguishing system:
Safety and environmental protection – the physical fire extinguishing with water as the fire extinguishing agent has no damage or pollution to the environment, protected objects, and personnel in the protected area.
Efficient fire extinguishing – the cooling rate is 100 times faster than that of the general sprinkler system. The high-pressure water mist is also penetrating, which can solve the problems of total submersion and occlusion, and can also prevent the resurgence of fires.
Purification function – it can purify smoke and exhaust gas, which is conducive to the safe evacuation of personnel and the fire fighting and rescue work of firefighters.
Shielding radiant heat–it has a good shielding effect on heat radiation, so as to prevent the spread of fire and quickly control the fire.
Small water loss – the water consumption is only 1-5% of the water sprinkler system, avoiding damage to the equipment and secondary pollution to the environment caused by a large amount of drainage.
Good electrical insulation – it can effectively extinguish fires of live equipment.
High reliability – after the system installation is completed, the system can be simulated and tested to increase the reliability of the system action.
Long system life–The pumps, valves, and pipe fittings are all made of corrosion-resistant materials, and the system life can be as long as 30 (60) years.
Flexible configuration – it can be used locally to protect an independent facility or a part of the facility; as a total submerged system, it can protect the entire space.
Easy installation – Compared with the traditional fire extinguishing system, the pipe diameter is small, only 10-32mm, which reduces the installation cost accordingly.
Easy maintenance – only water is used as the fire extinguishing agent, and the normal pressure is in the standby state, which greatly reduces the workload and cost of daily maintenance.
