The outdoor fire hydrant is a water supply facility installed on the fire water supply pipe network outside the building. It is mainly used for fire trucks to take water from the municipal water supply pipe network or outdoor fire water supply pipe network to put out fires. One of the important fire facilities.
Water pipe network design
High-pressure, temporary high-pressure, and low-pressure pipelines can be used for outdoor fire-fighting water supply pipelines. The outdoor fire-fighting water supply of towns, residential areas, enterprises, and institutions generally adopts a low-pressure water supply system, and it is often used in combination with domestic and production water supply pipelines. However, to ensure the safety of the water supply, high-pressure or temporary high-pressure water supply pipelines should be separated from production and domestic water supply pipelines, and independent fire-fighting water supply pipelines should be set up.
Classification of water supply pipelines
1. Classification according to water pressure requirements
(1) High-pressure water supply pipe network. It means that there is always enough pressure in the pipe network, and there is no need to use fire trucks or other mobile water pumps to pressurize the fire, but directly connect the hose and water gun from the fire hydrant to put out the fire. When the height of the building is less than or equal to 24m, the pressure of the outdoor high-pressure water supply pipeline should ensure that the water consumption for production, living, and fire fighting reaches the maximum, and when the water gun is arranged at the highest point of any building within the protection range, the full water column of the water gun should not be less than 10m. When the height of the building is greater than 24m, the fire shall be extinguished based on indoor fire-fighting equipment.
(2) Temporary high-pressure water supply network. In the temporary high-pressure water supply pipeline, the water pressure is not high at ordinary times, and the high-pressure fire pump is pressurized to make the pressure in the pipe network reach the pressure requirement of the high-pressure water supply pipeline. When there are high-rise buildings in towns, residential areas, or enterprises and institutions, a fire water supply system with high pressure or temporary high pressure both outdoors and indoors can be used, or a fire water supply system with high pressure or temporary high pressure indoors and low pressure outdoors. The pneumatic water supply device can only be regarded as a temporary high-pressure fire water supply system. Generally, petrochemical plants or Class A, B, and C liquid and combustible gas storage tank areas mostly use this kind of pipe network.
(3) Low-pressure water supply pipe network. It means that the water pressure in the pipe network is usually low, and the pressure of the water gun on the fire scene is formed by pressurizing the fire truck or other mobile fire pumps. The fire truck draws water from the fire hydrant of the low-pressure water supply pipe network. One is to directly absorb water from the fire hydrant with a suction pipe; In order to meet the needs of fire trucks to absorb water, the pressure of the fire hydrant at the most unfavorable point of the low-pressure water supply network should not be less than 0.1MPa. Generally, this kind of pipe network is used in towns and residential areas.
2. Classification according to the layout of the pipe network
(1) Ring-shaped fire water supply pipe network. The urban municipal water supply network and the outdoor fire-fighting water supply network of buildings should be arranged in a ring-shaped pipe network. The pipelines form several closed loops, and the water flows in all directions, which is safe and reliable. Its water supply capacity is 1.5-2.0 times that of the branched pipe network. However, when the outdoor fire water consumption is not greater than 15L/s, it can be arranged in a branched pipe network. There should be no less than 2 water inlet pipes from the horizontal pipe to the ring pipe network, and a certain distance should be kept between the water pipes, and connecting pipes should be provided. The pipe diameter of the outdoor fire water supply pipe network should not be less than 100mm, and if conditions permit, the pipe diameter should not be less than 150mm.
(2) Branch fire water supply network. In the initial stage of construction, or phased construction and large projects, or when the outdoor fire water consumption is not large, the outdoor fire water supply pipe network can be arranged as branch pipes. That is to say, the pipe network is set up in a tree-like shape. After the branches, the main lines are not connected with each other. The water flows in a single direction in the pipe network. When the pipe network is overhauled or damaged, the water will be cut off in front of it. Therefore, the scope of use of branched pipe networks should be limited.
Fire Requirements for Outdoor Fire Hydrant Arrangement
1. Basic requirements for setting. The installation of outdoor fire hydrants should be obvious and easy to find, so as to facilitate the operation of water discharge, and underground fire hydrants should also have obvious fixed signs near the ground. The above-ground fire hydrant is installed on the ground in a warm climate, and the underground fire hydrant is installed on the ground in a cold climate.
2. Outdoor firefighting settings in municipal or residential areas. Outdoor fire hydrants should be laid along the road. When the width of the road exceeds 60m, they should be installed on both sides and should be close to the intersection. The layout interval should not be greater than 120m, the distance from the edge of the road should not exceed 2m, the distance from the outer wall of the building should not be less than 5m, the distance from the outer wall of a high-rise building should not be greater than 40m, and the distance from the outer wall of a general building should not be greater than 150m.
3. The number of outdoor fire hydrants in the building. The number of outdoor fire hydrants should be determined according to the comprehensive calculation of their protection radius, flow rate, and outdoor firefighting consumption, and the flow rate of each hydrant should be 10-15L/S. For high-rise buildings, municipal fire hydrants within 40m can be included in the number of outdoor fire hydrants of the building; for multi-story buildings, municipal fire hydrants within a protection radius of 150m, if the fire water consumption is not greater than 15L/s, the building may not be equipped with outdoor fire hydrants.
4. Requirements for the setting of outdoor fire hydrants in industrial enterprises. For places such as process areas that use high-pressure or temporary high-pressure fire-fighting water supply systems, outdoor fire hydrants should be installed around them. The number should be confirmed according to calculations, and the distance should not exceed 60 meters. When the width of the process equipment area is greater than 120 meters, it is advisable to set up outdoor fire hydrants on the roadside in the process area. When structures such as process areas, storage tanks, storage yards, combustible gas, and liquid docks have large areas or high heights, and the flushing columns of outdoor fire hydrants cannot cover them, fire water cannons should be installed in appropriate places. When the financial high pressure or temporary high-pressure water supply system of the process area, storage tank area, storage yard, and other structures, the outdoor fire hydrants should be equipped with fire hoses and fire nozzles. In places where indoor fire hydrants need to be installed, such as the process unit area, they should be set at the rest platform of the process area.
5. The outdoor fire hydrants of structures such as Class A, B, and C liquid storage tanks and liquefied hydrocarbon storage tank areas shall be installed outside the fireproof lifts or protective walls. Fire hydrants within the range of 100 meters should not be counted in the usable quantity of the storage tank but can be used for cooling.
Design of outdoor fire hydrant protection radius and maximum layout spacing
1. The protection radius of the outdoor fire hydrant. The water protection radius of the outdoor low-pressure fire hydrant is generally considered as 9 hoses connected in series by fire trucks. The water gunners leave 10m motorized hoses on the fire scene. If the hoses are laid along the ground with a coefficient of 0.9, then the water supply distance of the fire trucks is (9× 20-10)×0.9=153m. Therefore, the protection radius of the outdoor low-pressure fire hydrant is 150m. The water supply protection radius of the outdoor high-pressure fire hydrant is considered as 6 water belts in series, and the same calculation, the protection radius is (6×20-10)×0.9=99m. Therefore, the protection radius of the outdoor high-pressure fire hydrant is 100m.
2. The maximum layout spacing of outdoor fire hydrants. The principle of outdoor fire hydrant spacing is to ensure that any part of the urban area is within the protection radius of two fire hydrants. According to the construction of urban roads, the maximum distance between municipal fire hydrants is X=√R2-(L/z)2, R is the maximum protection radius of fire hydrants, and L is the distance between street centerlines, which is about 160m according to urban planning requirements. It is calculated that the distance between outdoor low-pressure fire hydrants is X=127m, and the distance between outdoor high-pressure fire hydrants is X=60m. Considering the water supply needs of the fire scene, the maximum layout spacing of outdoor low-pressure fire hydrants should not be greater than 120m, and the maximum layout spacing of high-pressure fire hydrants should not be greater than 60m.
Flow and pressure design of outdoor fire hydrants
1. The flow rate of the outdoor fire hydrant. Talking about the flow of water supplied by the outdoor low-pressure fire hydrant. It depends on the number of water nozzles on the fire scene. Generally, each low-pressure fire hydrant only supplies water for one fire truck, and often two DC water guns with a caliber of 19mm are required. The fire site requires the water gun to be filled with a water column of 10-15m, so the flow rate of each water gun is 5-6.5L/S, 2 The flow rate of the water gun is 10-13L/S. Considering the leakage of the interface and the hose, the flow rate of each low-pressure fire hydrant is calculated as 10-15L/S. The water supply of each outdoor high-pressure fire hydrant is generally considered as a DC water gun with an outlet diameter of 19mm, and the full water column of the water gun is 10-15m, so the flow rate of each high-pressure fire hydrant is required to be not less than 5L/S.
2. The pressure of the outdoor fire hydrant. The flow rate of an outdoor fire hydrant is closely related to the pressure. If the outlet pressure is high, the flow rate will be large. The outlet pressure of the outdoor low-pressure fire hydrant is considered according to the water supply to the water tank of the fire truck. To ensure the flow of two water guns, the outlet pressure of the fire hydrant at the most unfavorable point should not be less than 0.1Mpa after calculation. The outlet pressure of the outdoor high-pressure fire hydrant water supply should meet the maximum water consumption. The water gun with a nozzle diameter of 19mm should be arranged at the highest point of the building. The calculated flow rate of each water gun should not be less than 5L/S. And the full water column should not be less than 10m. , 120m long hose water supply requirements. The outlet pressure of the fire hydrant at the most unfavorable point should be the sum of the required water pressure at the water column nozzle, the head loss of the water belt, and the elevation pressure difference between the outlet of the water gun and the outlet of the fire hydrant.