Technical introduction to a police door breaking device

[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

Internationally, methods of forced entry are relatively more advanced, with the United States, the United Kingdom, Germany, and Israel being among the leaders. Their primary tools include breach grenades, door cutters, tactical cutting torches, battering rams, and initiators. However, residential doors in these countries are mostly made of wood, and their forced entry techniques largely focus on destroying the lock or the door itself. In contrast, most doors in China are steel security doors with complex locking mechanisms, making these foreign breaching techniques not entirely suitable for our context. Additionally, given China's high population density, using such methods could pose varying degrees of risk to both hostages and rescue personnel.

Therefore, it is urgent to design an efficient and more comprehensive police door-breaking device that does not harm hostages or endanger the safety of rescue personnel. It primarily targets security doors, while also being capable of breaking through glass curtain walls and high-speed train windows.

3. Analysis of Anti-Theft Door Characteristics

Anti-theft security doors, commonly referred to as security doors, not only provide anti-theft functionality but also emphasize safety. According to the clear stipulations of China's "General Technical Conditions for Anti-theft Security Doors," a qualified door must maintain its integrity within minutes when subjected to attacks by conventional hand tools or portable power tools such as hand drills, preventing it from being pried open or forming an opening larger than square millimeters on the door panel. Additionally, within the square millimeter semicircular area around the locking points, the door should also resist attacks to prevent the formation of openings larger than square millimeters. Moreover, the locks used on security doors are a crucial aspect of their safety. These locks must undergo rigorous testing by the Ministry of Public Security's testing center and be certified as anti-theft locks with drill-resistant capabilities. The combination of such locks with the door body significantly enhances the security performance of the anti-theft door.

The materials used for manufacturing anti-theft doors are diverse, and they must undergo rigorous testing and national certification before they can officially be classified as anti-theft doors. This regulation ensures that all anti-theft doors on the market possess sufficient anti-theft and safety performance, thereby protecting the property safety of consumers. Standardized doors generally come in four specifications, with two different heights and two different widths, combining to form four different sizes of door frames.

According to the new standards, security doors must maintain their integrity and ensure the door panel cannot be opened even when subjected to destructive attacks within a specified time, such as drilling out the lock cylinder, prying off lock body connectors, or attempting to disengage the bolt by inserting prying tools through the upper or lower gaps. Additionally, the main bolt of the security door must extend to an effective length of no less than a specified measurement and should be equipped with a bolt stop device to enhance its anti-theft performance. These regulations are designed to ensure that security doors retain their robust anti-theft capabilities when faced with various destructive methods, providing safe and reliable protection for occupants.

The thickness of the steel plate material for the door frame should not be less than [specified value]. The thickness of the inner and outer panels of the door leaf should not be less than [specified value]. The panel material can be steel, stainless steel, steel/wood, steel, or other composite materials. The police door-breaking device introduced in this article primarily targets such steel anti-theft security doors. The door frame panel thickness is selected as [specified value], and the door panel thickness is chosen as outer panel/inner panel [specified value]. The total thickness of the door leaf is [specified value], with a height and width combination of [specified value]. Domestic steel anti-theft door panels are generally made of cold-rolled steel sheets, with # steel selected as the door panel material, featuring a yield strength of [specified value] and a density of [specified value].

4. Working Principle

The working principle of this police door-breaking device primarily involves mechanically igniting the propellant within the launch tube's power assembly. The propellant fully combusts inside the chamber, generating high-pressure gas from the gunpowder. As this gas continuously expands, the chamber pressure gradually rises. When the pressure reaches a specific threshold, the ignition tube is severed, causing the front and rear pistons to separate. Subsequently, the front piston, propelled by the expanding gas, drives the flexible barrier-breaking component forward until it exits the launch tube's muzzle. Meanwhile, the rear piston, under the force of the gas, rapidly pushes the counterbalance backward out of the launch tube, where it disperses. Ultimately, the front and rear pistons reach opposite ends of the launch tube, completing the entire firing process.

Blocked by the deformation ring and brake ring, the piston and gunpowder combustion are sealed within the launch tube, while the flexible barrier-breaking component is propelled outward at high speed under inertial force. Launched with a significant initial velocity due to inertia, the flexible barrier-breaking component strikes target obstacles such as anti-theft security doors, either penetrating or breaking through the barrier, enabling rapid entry for emergency personnel into indoor spaces.

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 reliable operation under extreme conditions.

To ensure the safety of the launch process, the launch tube must possess sufficient strength. For this purpose, we employ a multi-layer, variable-angle fiberglass winding process to manufacture the launch tube. This technique endows the tube with high strength, enabling it to withstand both high pressure and impact. Additionally, high-strength aluminum alloy braking rings are installed at both ends of the launch tube, 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 structural data on individual soldier equipment launching systems both domestically and internationally, and by drawing on existing mature product launch platforms in the country, the 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, among other components. The launch charge is composed of a powder box and propellant, where the powder box is made up of a powder box body and a powder box lid, 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 made from camphor.

(3) Balanced Body Structure Design

Considering the practical combat use, the device should be easy to carry and operate while ensuring minimal collateral damage to our personnel and surroundings after deployment. Therefore, a counterbalance structure is designed behind the power module. The counterbalance consists of uniformly sized plastic sheets stacked and bound together, with a mass equivalent to the front flexible breaching component. During launch, it serves to balance and counteract the recoil force.

(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 meet the requirements of storage, transportation, launching, as well as individual portability, ease of operation, rapid deployment, and firing for police assault door-breaching devices, the following technical measures are adopted: The system consists of a launching subsystem and a functional component system, designed with an integrated structure. The launch tube serves both as a packaging tube and a launch tube, fulfilling storage, transportation, and launching functions. The launcher features angle adjustment and a carrying harness, enabling portable背负 functionality. The launcher employs a three-legged rigid support system and utilizes a sealed balanced projectile ejection method, thereby reducing recoil and effectively minimizing system movement during launch. Through these technical measures, the system achieves integrated storage, transportation, and launching, ensuring simplicity and ease of operation.

(2) Balanced Body Projection Recoilless Technology

Unlike rocket launch methods (which rely on the reactive force generated by the backward ejection of gunpowder gas for propulsion