Technical introduction to a police door breaking device

Wang Fang Nie Xiaohu

[Abstract] This article presents the current state of door breaching technologies both domestically and internationally, and elaborates on the characteristics of security doors. In response to the features of domestic security doors, a police door breaching device with excellent comprehensive performance is introduced, focusing on its structural composition, working principles, and key technologies. Finally, an evaluation of the use of this door breaching device is provided.

【Keywords】Police｜Breaching Device

Currently, the counter-terrorism situation both domestically and internationally remains severe, with various violent crimes—especially indoor hostage situations—increasingly prevalent. When police execute criminal tasks, assault teams often need to quickly enter enclosed spaces such as indoors, inside vehicles, or within aircraft to swiftly subdue suspects and protect hostages. However, they frequently face entry challenges in practice. Therefore, if there were a simple and practical tool, it could rapidly and cost-effectively resolve these challenges.

Traditional hostage rescue methods primarily include two strategies: negotiation and forced rescue. However, when negotiations break down and the suspect is on high alert, forced rescue measures become a necessary option. In such cases, the assault team needs to quickly breach barriers such as doors and swiftly enter the premises, leaving no reaction time for the suspect. This approach aims to strike at crime with lightning speed, ensuring the safety of the hostages. Through such forced rescue measures, we can more effectively combat crime while maximizing the protection of the hostages' lives.

With the advancement of science and technology, door-breaking tools have been widely developed both domestically and internationally. Door-breaking devices can be categorized by power source into manual door-breaking tools, electric door-breaking tools, motorized door-breaking tools, hydraulic door-breaking tools, pneumatic door-breaking tools, explosive energy door-breaking tools, and other door-breaking tools. They are primarily used by firefighting, traffic police, and armed police forces for emergency rescue operations during natural or man-made disasters.

1. The Current State of Door-Breaking Technology in Our Country

The widely used door-breaking tools domestically include battering rams, door rams, shears, multi-function pliers, and metal cutters. Tools like door rams, shears, and multi-function pliers are quite effective against wooden doors due to their simplicity and low cost of use. However, they struggle to successfully breach steel doors and lack the element of surprise. Metal cutters can effectively break through security doors, but due to the long cutting time, they can easily alert terrorists and threaten the safety of hostages, making them unsuitable for surprise operations.

2. Current Status of Overseas Break-ins

The methods of breaching doors abroad are relatively advanced, with the United States, the United Kingdom, Germany, and Israel being among the leaders. Their main tools include breach grenades, door cutters, tactical cutting torches, battering rams, and initiators. However, the entry doors in these countries are mostly made of wood, and their breaching methods primarily focus on destroying the door locks or damaging the door itself. Since most doors in our country are security steel doors with complex locks, the breaching techniques from these countries are not entirely applicable to us.

Additionally, given the high population density in our country, the use of such methods could potentially cause varying degrees of harm to both hostages and rescue personnel. Therefore, it is imperative to design an efficient and comprehensive police door-breaking device that does not harm hostages or endanger the safety of the rescue team. This device primarily targets security doors, and is also capable of breaking through glass curtain walls and train windows.

3. Analysis of Anti-Theft Door Characteristics

Anti-theft security doors, commonly referred to as security doors, not only possess anti-theft functions but also emphasize safety. According to the clear stipulations of China's "General Technical Conditions for Anti-theft Security Doors," a qualified door should maintain its integrity within minutes when attacked by conventional hand tools and portable electric tools such as hand drills, preventing it from being pried open or forming an opening larger than a certain square millimeter on the door panel. Additionally, within a semi-circular area of a certain square millimeter around the locking points, it should also resist attacks, preventing the formation of an opening larger than a certain square millimeter. Moreover, the locks used in security doors are a crucial guarantee of their safety. These locks must be strictly tested by the Ministry of Public Security's testing center and proven to have anti-drilling functions, specifically designed for anti-theft purposes. Such locks, combined with the door body, can significantly enhance the security performance of the door. The materials used in the manufacture of security doors are diverse and must undergo rigorous testing and national certification before they can officially be called security doors. This regulation ensures that security doors on the market possess sufficient anti-theft and safety performance, thereby protecting the property safety of the general consumer.

National standard doors generally come in four specifications, with two options for height and two for width, combining into four different sizes of door frames. According to the new standards, security doors must maintain their integrity and ensure that the door cannot be opened even after enduring destructive attacks within a specified time, such as drilling out the lock cylinder, breaking the lock body connectors, or attempting to loosen the lock tongue by inserting prying tools through the gaps above and below. Additionally, the main lock tongue of a security door must extend to an effective length of no less than a specified measurement and should be equipped with a lock tongue stop device to enhance its anti-theft performance. These regulations are designed to ensure that security doors maintain strong anti-theft capabilities when faced with various destructive methods, providing safe and reliable protection for residents. The steel plate material of the door frame should have a thickness of no less than a specified measurement, and the thickness of the inner and outer panels of the door leaf should be no less than specified measurements. The material of the panels can be steel, stainless steel, steel/wood, steel, or other composite materials.

The police door breaching device introduced in this article primarily targets steel security doors of this type, with the door frame plate thickness selected as ., and the door panel thickness chosen as outer plate/inner plate ./. The total thickness of the door leaf is , with a height and width combination of . Domestic steel security doors generally use cold-rolled steel plates, with # steel selected as the door panel material, having a yield strength and a density of ./.

4. Working Principle

The working principle of this police door-breaking device primarily involves a mechanical firing mechanism to ignite the propellant within the launch tube's power assembly. The propellant fully combusts inside the chamber, generating high-pressure gunpowder gas. As the gas continuously expands, the chamber pressure gradually increases. When the chamber pressure reaches a specific value, the ignition tube is severed, causing the front and rear pistons to separate. Subsequently, the front piston, propelled by the gunpowder gas, drives the flexible barrier-breaking component forward until it exits the launch tube's mouth. Meanwhile, the rear piston, under the influence of the gunpowder gas, rapidly propels the balance body backward out of the launch tube and disperses. Ultimately, the front and rear pistons reach the two ends of the launch tube, completing the entire launch process. Under the action of the deformation ring and the brake ring, the pistons and the gunpowder combustion are sealed within the launch tube, and the flexible barrier-breaking component is launched at high speed due to the force of inertia.

Under the influence of inertial force, a flexible barrier-breaking component launched at a high initial velocity impacts target obstacle areas such as anti-theft security doors, either penetrating or breaking through the obstacles, allowing rapid entry into the interior by emergency personnel.

5. Structural Composition

This type of police door-breaking device is mainly composed of a launch tube, a mechanical firing mechanism, a flexible barrier-breaking component, and a balancing component.

（一）发射筒设计

The application of closed balanced projectile launch technology results in the high-pressure propellant gas being tightly confined within the launch tube during firing. Consequently, the launch tube must not only withstand the immense internal pressure generated by the propellant gas but also endure the significant resistance caused by the impact between the piston and the deformation ring when the piston is pushed to the tube's mouth. This technology demands that the launch tube possesses extremely high strength and stability to ensure normal operation under extreme conditions. To guarantee the safety of the launch process, the launch tube must have sufficient strength. To this end, we have employed a multi-layered, variable-angle winding process using fiberglass to manufacture the launch tube, which endows it with high strength, enabling it to withstand both high pressure and impact. Additionally, at both ends of the launch tube, we have used high-strength aluminum alloy brake rings, which not only meet the strength requirements during launch but also effectively reduce the overall weight of the system. Through these design measures, we ensure that the launch tube maintains its structural integrity and functional stability even under immense pressure and braking forces.

(2) Launch Structure Design

Through research and collection of domestic and international data on the structure of individual soldier equipment launching systems, and by drawing on the existing mature product launch platforms domestically, a launch structure was designed in accordance with the actual conditions of the product. The launch structure consists of a trigger safety, grip safety, firing mechanism base, firing pin, igniter, and igniter base.

The propellant charge consists of a cartridge case and propellant. The cartridge case is made up of a case body and a case cap, both constructed from nitrocellulose film and bonded together with butyl acetate to ensure the sealing of the propellant. The propellant used is single-base gunpowder.

(3) Balanced Body Structure Design

Considering the practical use in combat, it should be easy to carry and operate, and the police door-breaking device should not cause significant collateral damage to our personnel and surroundings after use. Therefore, a balance body structure is designed behind the power unit.

The balancing body is composed of uniformly sized plastic sheets stacked and bound together, with a mass consistent with the front-end flexible obstacle-breaking component. It serves to balance and counteract the recoil during launch.

(4) Design of Flexible Obstacle-Breaking Components

Since the target is a security door, breaching the security door and the locking points of the door frame requires the breaching component to carry or release a relatively large amount of kinetic energy onto the door body without penetrating it, causing significant inward deformation of the door body. This deformation allows the locking pins to disengage from the locking points, thereby breaching the security door and creating a rapid access path. After extensive testing, a flexible breaching component has been designed, featuring a special flexible outer covering material and an internal filling of kinetic energy transfer medium.

VI. Key Technologies and Advantages

(1) Portable Integrated Storage, Transportation, and Launch Technology

To enable the police assault door-breaking device to meet the requirements of storage, transportation, launching, individual carrying, simple operation, rapid deployment, and launching, the following technical measures are adopted: The system consists of a launching subsystem and a functional subsystem, adopting an integrated structure; simultaneously, the launching tube serves as both the packaging tube and the launching tube, providing storage, transportation, and launching functions; the launching frame features angle adjustment and carrying harness, offering carrying and backpacking functions; the launching frame employs a three-legged rigid support and a closed balanced body ejection launching method, thereby reducing recoil and effectively addressing the system's launching micro-motion.

通过以上技术措施，系统满足储运发一体化要求，操作简单、使用方便。

(2) Balanced Body Projection Recoilless Technology

Unlike rocket launch methods, which rely on the reactive force generated by the backward ejection of gunpowder gas to propel the functional unit forward, and are accompanied by noticeable rearward flames during both launch and flight, the balanced body ejection launch technology effectively neutralizes recoil by throwing a counterweight of equal mass to the functional unit backward, achieving a smoother launch process. Additionally, this technology utilizes the coordinated action of front and rear pistons to tightly seal high-pressure gunpowder gas within the chamber, thereby achieving a launch effect with minimal sound, light, flame, and recoil. This launch method not only enhances the concealment and safety of the launch but also provides strong support for the precise flight of the functional unit.

(3) No Collateral Damage Technology

The flexible breaching component is externally covered with a special flexible material and internally filled with a kinetic energy transmission device. After being fired from the barrel, it carries significant kinetic energy to act on the surface of the security door, breaching it. During the process of kinetic energy transmission for breaching, no damaging fragments are produced, and there is no significant collateral safety damage when entering the room through the breached door.

(4) Low-cost advantage

Comparing the existing advanced barrier-breaking equipment both domestically and internationally, the police assault barrier-breaking device offers an extremely high cost-effectiveness ratio when compared to the Rafael "Shoulder-fired Wall-breaching Long-range Ammunition" from Israel and the "Kinetic Door-breaching Ammunition" developed by a domestic research institute, which cost tens of thousands of yuan per set. After cost estimation, this set of police door-breaching equipment costs approximately a few thousand yuan per set. Moreover, it extensively uses raw materials such as aluminum alloy and engineering plastic parts, which are abundantly supplied domestically, meeting the requirements for mass production.

7. Evaluation of Practical Usage Effectiveness

The door breaching device was used to conduct tests on both outward-opening and inward-opening security doors, reliably impacting the security doors in all cases. The flexible breaching components showed no rebound and caused minimal collateral safety damage.

In a certain month and year, a special police unit conducted a trial of the door-breaking device. The overall evaluation indicated that the device met the relevant requirements and is one of the urgently needed equipment for special police forces.

references

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Wang Zhenqun, Liu Zhongxi. Preliminary Study on the Issue of Breaking and Entering Through Security Doors // China Fire Protection Association, Anhui Provincial Fire Brigade. Proceedings of the Annual Conference on Science and Technology of the China Fire Protection Association. China Science and Technology Press.

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Editor of this issue: Chen Luyang

This issue reviewed by: Lin Yingxi

Layout Design: Zhou Kaikai

Article Source: "China Military-to-Civilian Magazine"

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