【 Weak current College 】 fire system knowledge

Fire protection system is and fire detection and alarm system at the same time settings. In fire detection and alarm system to detect fire danger, will start the fire-fighting system, to achieve the purpose of extinguishing fire. The following describes the principle of fire-fighting system, and to fire fighting systems to illustrate the application of fire-fighting system.

With the development of fire-fighting techniques, fire extinguishing system has been developed, the most common water extinguishing systems, automatic sprinkler systems, carbon dioxide fire suppression systems, foam extinguishing systems, dry powder fire extinguishing systems.

1. water extinguishing systems

(1) the role of water in fire

Water is a natural agent. Water fire extinguishing function has the following four aspects:

? Cooling effect. Because water has a very large heat capacity and latent heat of evaporation, water is very good heat absorbing material. When water injection to combustion material surface, because the water of the thermal, combustion temperature of the material, when the temperature drops below the ignition, the material stop burning.

? Suffocation. Water heating, vaporization of volume expansion, the burning material around a large steam range, which hindered the fresh air into the combustion zone, the combustion of oxygen concentration in the region, the fire.

? Emulsified. When drops of water or spray water in some water-immiscible viscous liquid surface, can produce emulsified. Due to continuous water, forming a imposed emulsion layer, the surface of the liquid is cooled, flammable vapors resulting slowdowns, fire is put out.

Combustible substance? dilution. Many combustible material is easily soluble in water, liquid fire extinguishing with water, with water, flammable substances, flammable vapor concentration reduces production slowdowns, flash point gradually increased. When the combustible substance concentration drops to a value sufficient to then support combustion, the combustion is terminated.

(2) water fire suppression system of hoses

Water fire extinguishing system consists of fire pumps, fire mains, hydrants, fire hoses, water gun, water fog, etc.

In order to ensure the reliability of water extinguishing systems, piping layout has the following 3 ways:

? The ring system. Will fire mains arranged circular, in any one side of the half-ring fails, the water can be passed from the other side. This system enables water fire extinguishing system with high reliability, he is widely used for passenger ships, fishing, processing vessels with a greater scale.

? Linear system. The system will fire mains is divided into two or three main pipe, service on board the first building, and tail lift open deck. This system is widely used in oil and dry cargo vessels, for some auxiliary vessels, fishing boats and tugs, generally not separated into several main pipe.

Joint-system?. This system applies to larger ships, such craft generally in the first set a fire pump, adopt the tail including the superstructure; circular fire mains in the cargo hold regional and first use of linear fire mains.

2. automatic sprinkler system

Automatic sprinkler system is to water as a medium, he is fixed fire-extinguishing system in the history of the longest and widest range of a fire extinguishing system. Automatic sprinkler systems have a closed system and two open system. In passenger ships, cargo ships, tankers, etc of accommodation and service premises, the general use of closed-system. But in serious danger zone, once the fire spread very quickly, often uses open-systems, such as offshore platform technology area, such as LPG ship's deck.

Automatic sprinkler system pressure pipeline network in peacetime by water keep a certain pressure. When a fire occurs, start spray nozzles and the pressure is the pressure inside the tank. When the pressure of water pressure drops to a set value, pressure water tank pressure relays automatically start fresh water pump to the pipeline. Due to the large amounts of water sprinkler, water pump supplied water cannot guarantee the supply of water to water pressure of work, the control valve pressure relays automatically starts the sea water, sea water pump to supply. As the sea water pump displacement is relatively large, can guarantee maximum protection zone sprinkler work flow.

In each section of the pipeline are equipped with pressure relay and flow indicator. When a — partition fire, started sprinkling nozzles in the area, which pipeline in water flow, the flow of water is greater than the set value, the flow meter to send a signal to the control room, the fire, and water spray nozzle has begun. Pressure relays monitor the pressure in the pipe network, when the pressure is lower than the set value, the control room gives a low water pressure alarm, and start the sea water pump.

According to the control valve and nozzle, automatic sprinkler systems can be divided into wet and dry system, system, preaction system, open system.

? Wet system

Wet system is a broader application, the structure is simple, automatic sprinkler systems. The system of pipe and nozzle is always full of water, and keep a certain pressure nozzle once started, the water sprays, water spray at once speedy, fire and extinguishing success rate is quite high.

Wet system is mainly composed of closed sprinklers, wet alarm valve equipment, hydraulics, water supply pipelines and control box, etc, the system has an automatic fire detection and alarm and water features.

?-Dry system

In dry system, within the pipes and the nozzles are normally not sufficient water, and filled with compressed air. Dry system by wet or dry valve, closed sprinkler, water alarm, automatic exhaust Accelerator, inflatable devices and water pipelines, the system can independently perform automatic detection, alarm and sprinkler mandates.

Normal, dry, wet or valve is closed valve inlet side and is connected to the water source and full of water, the valve outlet side and is connected to the water distribution and sewer are filled with compressed air. Inflatable's role is to monitor the system piping work, pipeline damage and leaks, but also prevents water loss and pipeline of icing. Compressed air in the dry systemPressure must remain within the scope of the set, if the air pressure drops, the system low pressure pressure relay to control box makes low air pressure alarm signal, remind the person on duty.

When a fire occurs, because of the closed-head, high temperature and open water dry pipe gas pressure dropped rapidly, resulting in wet or dry valve outlet side pressure drops, dry, wet or valve automatically open, water enters the water water supply to the dry pipe sprinkler, water spray nozzle began. In wet or dry, the valve is open at the same time, the alarm will automatically turn on the water, and audible signals.

System monitoring water pressure pressure relays installed in wet or dry, valve inlet side, when this valve opens and the distribution of water sprinkler pipe and dry, water pressure will decrease, the pressure relay sends a signal that the control box to start the fire pump water supply to the system.

Dry-type system in the warm climate, can become wet system.

Preaction system?

Preaction system is the technology of automatic fire alarm and sprinkler systems in organic combination. This system is mainly composed of closed type nozzle, automatic preaction valve, pneumatic, water supply pipelines and automatic fire detection and alarm installations.

In the absence of fire, the system of water distribution system with dry dry pipe full of compressed air as. When a system of fire detectors detect this protected area in the event of a fire, the detector to the alarm control box makes fire alarm signal, control box immediately signals, preaction valve opens to the distribution of water sprinkler pipe and dry, allowing systems to the wet system. At this point, if the fire continues to develop, closed sprinkler temperature sensor element melts or falls off, start sprinkling nozzles. If the watch personnel receive the detector signal, issued by the fire in time to the scene to fight fires, the closed-head does not automatically spraying water, reducing water losses.

In effect, preaction valve opening protected by alarm control box control, and is not affected by water pressure of compressed air in the dry tube size. When distributing dry pipe rupture occurred because of an accident, the air pressure drops in the pipeline, and the minimum pressure set bits, i.e. the issue of fault alarm signal, so you can work on the pipeline state is automatically monitored.

-Open System

Open system mainly by rain valve, open type nozzle, automatic fire detection and alarm equipment, water alarm and water pipelines, etc. Shower valve open, by controlling the automatic fire detection equipment, shower valve once opened, all the sprayer and spray.

In the open-system, when you open sprinkler nozzle selection high-speed, secure area when you like the rain water, known as the deluge system; when open nozzle selection of water sprinkler, water is made up of a curtain, known as the water curtain system; when I turn on the sprinklers for water mist spray water nozzle, the system is formed when water spray, water fog system is called. According to the different protected object selection of different nozzle.

No fire, the deluge valve is closed valve inlet side communicates with water source, valve outlet side and water distribution pipes, water pipes in ATC.

When fire detectors detect protected areas within the fire, the fire detector issued to alert the control box, fire alarm signal alarm control box received the fire signals automatically opens immediately after the shower valve and hydraulic alarms, water enters the water dry pipe sprinkler water supply to the drive, the system to work. By fire detector alarm signal to the sprinkler sprinkling of time can be controlled in a very short period of time, even within a few seconds to complete the head movements.

3. carbon dioxide extinguishing systems

Carbon dioxide fire extinguishing system is via the protection of its fire fighting equipment to regional cast — quantitative CO2 extinguishing agent, thus reducing the protection area of oxygen in the air, the combustion is not required by the oxygen concentration. Experiments show that when the air carbon dioxide levels reach 30% ~ 50%, you can make the most of the combustible material is burning. When the carbon dioxide content in the air reaches 44%, gasoline vapors and other inflammable gas explosion.

Carbon dioxide is used as the extinguishing agent, and water compared with no stain, no water loss and non-conductive characteristics, so CO2 extinguishing system is widely used.

Carbon dioxide fire extinguishing system is mainly used for the following ship premises protection: cabin, an oil tanker cargo tanks, engine room, engine room control room, Purifier, oil separation equipment, air compressor room, cargo compartments, transmission gear, low speed diesel engine of depuration, generator room, the cargo control room, painting rooms, the emergency generator room. If the premises are the same, can be used as a premises.

? High pressure CO2 system

Usually ship with high-pressure carbon dioxide fire extinguishing system is mainly composed of carbon dioxide cylinders, pneumatic/manual bottle head valves, control valves, cast, cast time delay valves, pneumatic and cast pipe, valves and nozzles, etc.

Currently, internationally is the carbon dioxide cylinder 68L/45kg, steel cylinders with pneumatic/manual bottle valve, can be pneumatic remote control from a distance, you can also manually cast on site. When a large number of steel bottle bottle head valve with pneumatic hose to connect, you can be in long distance remote control cast many cylinders, the cylinders of carbon dioxide gas pipeline through emitting into the specified protection area.

Remote control cast box by selecting Start cylinder and control valve. Starting cylinder storage of carbon dioxide or nitrogen, as the starting cylinder head valve gas bottles. Control to select the main cast of the pneumatic valve valve and cylinder bottle valve order selection control.

Time delay unit's role is to ensure that pneumatic cast valve to release carbon dioxide carbon dioxide cylinders, General before opening the delay time for 30s and 60s.

For different types of vessels, fixed CO2 fire-extinguishing system configurations vary, but the principle is similar.

Low pressure CO2 system?R>
In recent years, with the large tankers, container ships and a large number of applications of liquid packing, protection zone space increases, CO2 requirements sometimes 10t above. If used at normal temperature and pressure storage method, you need more than 200 bottles, a lot of pressure vessel fillers and complex control systems, but also to manage difficult, thus developed low pressure CO2 system.

Carbon dioxide storage pressure and temperature, the higher the temperature, the larger the memory pressure. Low pressure CO2 systems and high-pressure carbon dioxide system, only carbon dioxide storage in different ways, its cast method is the same.

In low pressure CO2 system, carbon dioxide storage for steel class pressure vessel, he can withstand the 2.0MPa at-20 ° c temperature. Carbon dioxide shall be composed of at least two refrigeration unit in the desired temperature, each refrigeration appliance can stay alone stipulate the conditions of storage. Storage container should include a solid insulation, refrigeration equipment failure stops to the carbon dioxide pressure increases the safety function will be a long delay. Safety valve once opened, carbon dioxide vapor to escape, so that the surface of the liquid evaporates again out of gas, resulting in a cooling effect, causing the temperature in the storage containers, pressure will decrease, even at high temperatures in summer, after 24h won't have a lot of gas escape. When stored at 2% escaping gases should be automatic alarm.

Usually in CO2 requirements meet the 10t above that uses low pressure CO2 system. The larger, low pressure CO2 requirement CO2, the more significant of superiority. The advantages of low pressure CO2 systems are:

? Total weight reduction of 50% or more;

The device structure is simple and tube;

? Container pressure stability, low pressure is not easy to leak.

4. foam extinguishing systems

Foam applicable to fight oil fire, which includes combustible liquids or combustible solid fire. Early foam is produced through a chemical reaction to the current majority has been replaced by mechanical foam.

No matter what type of foam concentrate, with water at a ratio to mix, usually take 3% or 6%. And water mixture of foam mixed fluid in the hydraulic field into the foam gun, foam gun or other foaming device. On these devices, foam mixture produced turbulence and inhalation of air, air and foam mixture in foaming equipment within the bubble filled with air bubbles, and spray into the protection zone.

Jet in the surface of the combustion of liquid, foam forms a continuous foam layer, and the adoption of the following physical role to complete the fire:

» Cooling

When the surface temperature of fuel combustion is relatively high, at 90 ~ 350 ° c range, the first arrival of foam on the surface of the fuel is heated, the foam in the water is vaporized, thereby absorbing surface contact with some of the fuel heat, reducing fuel surface temperature. Because of the foam on the surface of the fuel flow diffusion, foam layer of an area of widening, cooling the surface of the fuel was also growing until the entire combustion surfaces are covered with foam layer. When the foam layer thickness is increased to a certain extent, and fuel surface is cooled to the vapor is insufficient to sustain combustion, flame is extinguished, the fire was put out.

? Suffocation

Foam thermal effect of the surface of the fuel and the flame of thermal radiation effects, where the surface water in the fuel, the vaporization of water vapour generated by the fuel oxygen concentration near the surface, has weakened the flame burning intensity, this helps foam in the accumulation of fuel and the foam on the surface layer of thick, while the foam layer thickness is increased to a sufficient thickness, completely suppress the evaporation of fuel and the fuel and air completely separated, and thus lead to flame out.

? Trip effect

In foam, foam will enable has been overridden by fuel surface and has not been foam-covered fuel the flames from the surface, prevents the flame and has been covered by foam on the surface of the fuel and direct contact with the flame on the part of the trip fuel surface radiation helps foam cooling role and contribute to the strengthening of suffocation.

Type of foam concentrate for more. From foaming ratio, can be divided into power, the times, low foam concentrate. From use, can be divided into ordinary foam concentrate and multifunctional foam concentrate.

In the late 1970s, developed a new type of foam extinguishing systems, fixed fire-extinguishing foam spray-type. This system is mainly used in the ship's cargo oil tanks, aircraft libraries and garage, etc. This system when the foam injection is finished, you can also spray water continuously. Foam spray system operation principle and dry sprinkler systems are the same, as long as the open-water spray systems plus bubble bath Cabinet, foam concentrate and proportioner, open nozzle into foam spray head, dry sprinkler system becomes a foam spray system.

5. dry powder fire extinguishing system
According to the International Maritime Organization issued in 1975, the IGC must be equipped with a dry powder fire extinguishing system, so that in the cargo area of deck fire.

Due to the dry powder of relative density is relatively large, the role of the air flow can cover the fire will not be dispatched on the air. Use extinguishing, dense clouds of smoke and flame powder, can reduce residual flame on combustion of surface heat radiation. The basic material of extinguishing agent in the heat of the flame will be subjected to a series of decomposition reaction, the reaction is generally is endothermic reaction, can absorb the heat of the flame component. These decomposition reaction of some inert gases such as carbon dioxide, water vapor, oxygen concentration in the region has a dilution effect. Ammonium salts and other chemical compounds also has the lead role of carbide, he attached to the burning of solid surface, enable the formation of solid surface, carbide layer of carbonation is poor conductor of heat, the combustion process temporarily become slow, the temperature of the flame. But the main fire effect for powder chemical inhibition, in maintaining combustion chain counterShould the free radicals in the key is OH and H. When the dry powder into the combustion zone and flame mixed, can simultaneously capture OH and H, lots of dry powder injection into the combustion zone, OH and H soon be depleted, chain-type combustion reaction is stopped, the flame will be extinguished.

Fixed fire extinguishing system is mainly divided into two types, namely, manual fire extinguishing system and automatic fire extinguishing system. Regardless of the system, devices launch after the action steps are roughly the same.