The dry powder fire extinguishing system is one of the four traditional fixed fire extinguishing systems (water, gas, foam, dry powder) and is widely used. It has attracted the attention of industrially developed countries, such as the United States, Japan, Germany, and the United Kingdom, which have successively formulated dry powder fire extinguishing system specifications. In recent years, due to the damaging effect of halon on the atmospheric ozone layer, the fire protection community is exploring alternative technologies for halon fire extinguishing systems, and the dry powder fire extinguishing system is one of the more mature technologies.
Applicable and non-applicable scope of dry powder fire extinguishing system
Application:
- Gas fires where the gas source can be cut off before extinguishing the fire.
Flammable, combustible liquid, and meltable solid fires.
Combustible solid surface fire. - Fire caused by live equipment.
Not applicable: - Nitrocellulose, explosives, and other chemical substances and strong oxidants that can be oxidized rapidly without air.
- Potassium, sodium, magnesium, titanium, zirconium, and other active metals and their hydrides.
Some regulations on the design of dry powder fire extinguishing system
Dry powder fire extinguishing systems can be divided into total flooding fire extinguishing systems and local application fire extinguishing systems according to the application mode. The total flooding fire extinguishing system should be used to extinguish the fire in the closed space; the local application fire extinguishing system should be used to extinguish the fire of the specific protected object.
The protection area using the total flooding fire extinguishing system shall meet the following requirements:
- The total area of the openings in the protection zone that cannot be automatically closed when spraying dry powder should not exceed 15% of the total internal surface area of the protection zone, and the openings should not be located on the bottom surface.
- The fire resistance rating of the enclosure structure, doors, and windows in the protected area should not be less than 0.50h, and the fire resistance rating of the suspended ceiling should not be less than 0.25h; the allowable pressure of the enclosure structure, doors, and windows should not be less than 1200Pa.
The protected objects using a local application fire extinguishing system shall meet the following requirements: - The air velocity around the protected object should not exceed 2m/s. When necessary, wind protection measures should be taken.
- Between the nozzle and the object to be protected, there should be no obstructions within the range of the spray angle of the nozzle.
- When the protected object is a flammable liquid, the distance from the liquid surface to the edge of the container shall not be less than 150mm.
When there are combustible gas, flammable, and combustible liquid supply sources in the protected area or protected objects, the gas and liquid supply sources must be cut off before or at the same time as the dry powder fire extinguishing system is activated.
Sodium bicarbonate dry powder fire extinguishing agent should be used for combustible gas, flammable, flammable liquid, and meltable solid fire; ammonium phosphate dry powder fire extinguishing agent should be used for combustible solid surface fire.
Total flooding fire extinguishing system
The design concentration of the fire extinguishing agent for the total flooding fire extinguishing system shall not be less than 0.65kg/m³.
The dry powder injection time of the total flooding fire extinguishing system shall not be greater than the 30s.
The nozzle layout of the total flooding fire extinguishing system shall make the fire extinguishing agent evenly distributed in the protected area.
Local Application Fire Suppression Systems
The design of local application fire extinguishing systems can adopt the area method or volume method. When the burning part of the protected object is a plane, the area method should be used; when the area method cannot be used to completely cover all surfaces, the volume method should be used.
The dry powder injection time of the locally applied fire extinguishing system indoors shall not be less than the 30s; the dry powder injection time of the locally applied fire extinguishing system outdoors or indoors where there is a risk of re-ignition shall not be less than 60s.
When using the area method for design, the following requirements shall be met:
- The calculated area of the protected object shall be the vertical projected area of the protected surface.
- The dry powder delivery rate and corresponding protection area of the overhead sprinkler head should be determined by the distance from the outlet of the sprinkler head to the surface of the protected object; the protection area of the slot-side sprinkler head should be determined by the dry powder delivery rate selected by the design.
Prefabricated fire extinguishing device
Prefabricated fire extinguishing devices shall meet the following requirements:
- The storage capacity of fire extinguishing agent shall not exceed 150kg.
- The length of the pipeline shall not exceed 20m.
- The working pressure shall not be greater than 2.5 MPa.
A protected area or protected object should be protected with a set of prefabricated fire extinguishing devices.
The maximum number of prefabricated fire extinguishing devices used in a protected area or protected object shall not exceed 4 sets, and they shall be activated at the same time, and the action response time difference shall not be greater than 2s.
Components of dry powder fire extinguishing system
Storage device
The storage device should be composed of a dry powder storage container, container valve, safety pressure relief device, driving gas storage bottle, bottle head valve, collecting pipe, pressure reducing valve, pressure alarm, control device, etc. And should meet the following requirements:
- The dry powder storage container should comply with the current national standard “Pressure Vessel Safety Technical Supervision Regulations”; the driving gas storage bottle and its filling coefficient should comply with the current national standard “Gas Cylinder Safety Supervision Regulations”.
- The design pressure of the dry powder storage container can be 1.6 MPa or 2.5 MPa; the filling coefficient of the dry powder fire extinguishing agent should not be greater than 0.85; the pressurization time should not be greater than the 30s.
- The dry powder storage container should meet the requirements of driving gas coefficient, dry powder storage capacity, dry powder delivery rate, and pressure at the outlet of the output container valve.
The driving gas should be an inert gas, preferably nitrogen; the moisture content of carbon dioxide should not exceed 0.015% (m/m), and the moisture content of other gases should not exceed 0.006% (m/m); the driving pressure should not exceed the maximum working pressure of the dry powder storage container.
The arrangement of storage devices should be convenient for inspection and maintenance and should avoid direct sunlight. The ambient temperature should be -20~50°C.
Select Valves and Sprinklers
In the combined distribution system, each protection area or protection object should be equipped with a selection valve. The position of the selector valve should be close to the dry powder storage container, and it is convenient for manual operation,China fire fighting equipment manufacturer inspection, and maintenance. The selector valve shall be provided with a permanent nameplate indicating the protected area.
The selection valve should be a quick-opening valve, and its nominal diameter should be equal to the nominal diameter of the connecting pipe.
The selector valve can be driven by electric, pneumatic, or hydraulic, and should have a mechanical emergency operation method. The nominal pressure of the valve should not be less than the design pressure of the dry powder storage container.
When the system is started, the selector valve should be opened before the valve of the output container is actuated.
The sprinkler head should have a protective device to prevent dust or foreign matter from clogging the spray hole, and the protective device should be automatically blown off or opened when the fire extinguishing agent is sprayed.
The single-hole diameter of the nozzle shall not be less than 6mm.
Pipes and accessories
Pipes and accessories should be able to withstand the working pressure at the highest ambient temperature, and should meet the following requirements:
- Pipes should be made of seamless steel pipes, and their quality should meet the current industry standards; pipes and accessories should be treated with anti-corrosion treatment on the inner and outer surfaces, and anti-corrosion methods that meet environmental protection requirements should be adopted.
- In an environment that is corrosive to the anti-corrosion layer, the pipes, and accessories can be made of stainless steel, copper pipes, or other corrosion-resistant non-combustible materials.
- The pipeline for conveying the start-up gas should be made of copper pipe, and its quality should meet the industry standard.
- The pipe network should have a purge port.
- Reducer pipes should be used when changing the diameter of the pipe.
- The turning of the main pipe should not be immediately connected to the branch pipe; the turning of the pipeline should meet the requirements of Appendix B.
- Four-way pipe fittings should not be used for pipe branches.
- When the pipeline turns, it is advisable to choose a bent pipe.
- Pipeline accessories should pass the inspection and approval of professional testing institutions.
Pipelines can be threaded, grooved (clamped), flanged, or welded. Pipes with a nominal diameter equal to or less than 80mm should be threaded; pipes with a nominal diameter greater than 80mm should be connected with grooves (clamps) or flanges.
The closed pipe section between the valves in the pipe network shall be provided with a pressure relief device. The pressure of the pressure relief action is taken as (115±5)% of the working pressure
On the main pipeline of the fire extinguishing system leading to the protected area or protected object, a pressure signal or flow signal should be installed.
Dry powder fire extinguishing system control and operation
- The dry powder fire extinguishing system should be equipped with three starting modes: automatic control, manual control, and mechanical emergency operation. When the locally applied fire extinguishing system is used in a protective place where people are often present, the automatic control start mode may not be provided.
- When an automatic fire alarm system is installed, the automatic control of the fire extinguishing system shall be activated only after receiving two independent fire detection signals, and the spraying shall be delayed, and the delay time shall not be greater than the 30s, and shall not be less than the increase pressure time.
- The manual starting device of the total flooding fire extinguishing system should be set in a place outside the protection zone adjacent to the exit or evacuation passage for easy operation; the manual starting device of the local application fire extinguishing system should be set in a safe place near the protected object. The installation height of the manual starting device should be such that its center is 1.5m above the ground. All manually activated devices should be marked with the name of the corresponding protection zone or protection object.
- A manual emergency stop device should be installed close to the manual start device, and its installation height should be the same as that of the manual start device. The manual emergency stop device shall ensure that the fire extinguishing system can be stopped during the delay period after activation and before the discharge of the fire extinguishing agent. After using the manual emergency stop device, it should be ensured that the manual start device can be started again.
- The power supply and automatic control of the dry powder fire extinguishing system shall comply with the relevant provisions of the current national standard “Code for Design of Automatic Fire Alarm System” GB 50116. When a pneumatic power source is used, the gas pressure and gas consumption required for system operation and control should be guaranteed.
- The prefabricated fire extinguishing device may not be equipped with a mechanical emergency operation starting method.
Safety requirements for dry powder fire extinguishing system
- Sound and light fire alarms should be installed in the protected area and at the entrance, and dry powder fire extinguishing agent spray indicator door lights and permanent signs of the dry powder fire extinguishing system should be installed at the entrance of the protected area.
- The aisles and exits of the protection zone must ensure that people can evacuate safely within 30 seconds.
- The door of the protected area should be opened in the direction of evacuation, and it should be able to close automatically. In any case, it should be able to be opened in the protected area.
- An automatic and manual switch should be installed at the entrance of the protection zone. The installation height of the transfer switch should be such that the center position is 1.5m from the ground.
- For the underground protection zone and the above-ground protection zone without windows or with fixed windows, an independent mechanical exhaust device should be installed, and the exhaust outlet should lead to the outside.
- For the local application of the fire extinguishing system, fire sound and light alarms should be installed.
- When the system pipeline is set in a place with an explosion hazard, the metal parts such as the pipe network should be grounded against static electricity, and the antistatic grounding design should comply with the current relevant national standards.
