Dry powder fire extinguishing systems use dry powder fire extinguishing agents. Dry powder fire extinguishing agent is a fine powder capable of extinguishing fires. When discharged, it forms a mist and is widely used to fight specific types of fires. Dry powder fire extinguishing agents belong to solid particles. Even ultra-fine dry powder fire extinguishing agents are only solid powders with a particle size of no more than 15μm. After being discharged, they cannot be effectively cleaned and are prone to absorbing moisture. Dry powder fire extinguishing agents tend to settle after being discharged, have poor dispersion performance, and are easily obscured, making it difficult to meet the requirements of uniform and consistent fire extinguishing concentration, let alone the immersion time requirements. The current standards do not support the application of dry powder fire extinguishing systems. In automatic fire extinguishing systems, dry powder fire extinguishing systems are mainly applied in specific places that are sensitive to dry powder fire extinguishing agents, such as certain petrochemical fires, metal fires and other places.

1） After the dry powder fire extinguishing agent is sprayed, it is difficult to meet the requirement of uniform and consistent fire extinguishing concentration. Dry powder fire extinguishing agents belong to solid powders, and even ultrafine dry powder fire extinguishing agents are only solid powders with a particle size of no more than 15 μ m. Dry powder fire extinguishing agent settles quickly after spraying, has poor dispersion performance, is easily blocked, and is difficult to meet the requirements of uniform and consistent fire extinguishing concentration, especially difficult to penetrate into the interior of equipment and gaps in wires and cables, making it impossible to effectively extinguish internal fires and wire and cable fires.  
 
2） After the dry powder fire extinguishing agent is sprayed, it cannot effectively meet the requirements of fire extinguishing immersion time. To ensure effective fire extinguishing, automatic fire extinguishing systems typically require a certain duration of operation or fire extinguishing immersion time to ensure effective fire extinguishing and prevent the recurrence of fires. The automatic fire extinguishing system using water, foam and other extinguishing agents usually adopts a continuous action mode, for example, the continuous spraying time of closed automatic sprinkler system and automatic tracking and positioning jet fire extinguishing system is usually not less than 1.00h; the continuous liquid supply time of foam fire extinguishing system is usually 10~60min. Gas fire extinguishing systems usually require a guaranteed fire extinguishing immersion time. For example, when using heptafluoropropane and IG541 mixed gas fire extinguishing systems to extinguish solid surface fires such as wood, paper, and fabric, the fire extinguishing immersion time should not be less than 20 minutes. The dry powder fire extinguishing system adopts a one-time spraying method. According to standard regulations, the dry powder spraying time of the fully submerged fire extinguishing system will not exceed 30 seconds. Due to the relatively fast settling of the dry powder, it is difficult to ensure the fire extinguishing immersion time and effective protection cannot be formed. Therefore, the dry powder system is not suitable as an automatic fire extinguishing facility.

Dry powder fire extinguishing systems cannot be effectively cleaned after being discharged and thus cannot be applied in places with cleanliness requirements.

After the dry powder fire extinguishing system is discharged, the dry powder will deposit on the floor and the surface of the equipment. When it deposits inside the equipment or in the gaps of wires and cables, it is difficult to clean and affects the heat dissipation of the equipment. In particular, dry powder is prone to absorbing moisture and forming lumps, which may affect the operation of equipment or pose safety hazards. Dry powder fire extinguishing systems are particularly unsuitable for application in places with cleanliness requirements such as electronic equipment.

The main application methods of dry powder fire extinguishing system.     
Dry powder fire extinguishing systems can be divided into total flooding fire extinguishing systems and localized application fire extinguishing systems according to their application methods. When designing a dry powder fire extinguishing system, a reasonable application method must be determined. A fully submerged fire extinguishing system should be used to extinguish fires in enclosed spaces; Local fire extinguishing systems should be used to extinguish fires involving specific protected objects.       
(1) Total submergence fire extinguishing system: Spray a certain concentration of dry powder into the protected area within a specified time and evenly fill the entire fire extinguishing system of the protected area. The dry powder spraying time of the fully submerged fire extinguishing system should not exceed 30 seconds
(2) Local application fire extinguishing system: mainly composed of an appropriate supply source of fire extinguishing agent, which can directly spray the fire extinguishing agent onto the object on fire or areas considered dangerous. The dry powder spraying time of indoor localized fire extinguishing systems should not be less than 30 seconds; the dry powder spraying time of outdoor or indoor localized fire extinguishing systems with reignition hazards should not be less than 60 seconds. Localized fire extinguishing systems are suitable for local protection objects in large spaces (such as oil tank protection in factories) and are usually only suitable for pipeline fire extinguishing systems.     
(3) As can be seen from the above, the total flooding fire extinguishing system and the local application fire extinguishing system are completely different application methods, and the spraying time requirements are opposite. The total flooding fire extinguishing system requires the shortest spraying time (not more than 30 seconds), and requires the formation of a uniform and consistent fire extinguishing concentration in the protective zone and sufficient immersion time. The local application fire extinguishing system requires extending the spraying time as much as possible (not less than 30s or 60s) under a certain spraying intensity.