If China invades Taiwan by force, one of the methods will be a missile attack. Regardless of whether the PLA uses tactical ground-to-ground missiles or cruise missiles, they are all types of aerial bombs and will explode according to the original fuze setting method. After deducting the intercepted missiles, the remaining missiles that did not hit the original target will still explode, but the damage is not the original target.
Explosion characteristics and actual power
An explosion is an extremely rapid release of energy in the form of light, heat, sound and shock waves. During the explosion, a very fast chemical reaction occurs first, which converts the solid or liquid explosive material in the explosive into a high-temperature, dense, and high-pressure gas. The gas initially expands at a very high speed, trying to equilibrate with the surrounding air, causing a shock wave. Shock waves consist of extremely highly compressed air traveling at supersonic speeds outward from their source. About one-third of the chemical energy in high explosives is released during detonation, while the remaining two-thirds burn relatively slowly.
As the shock wave expands, the pressure drops rapidly in inverse proportion to the cube of the distance. When encountering a surface within the blast line of sight, the shock wave is reflected by the surface and amplified, sometimes by as much as 13 times. Pressure also decays exponentially rapidly over time, typically only for a few milliseconds.
When an explosion occurs in a narrow street or alley, the shock wave will continuously reflect and amplify between the surfaces of high-rise urban buildings, causing greater damage, and the diffraction effect caused by the corners of the buildings will limit the airflow and prolong the duration of the shock wave; The shock wave compresses most of the gas atoms on the surface, and later in the explosion process the interior becomes a vacuum creating a negative suction, and the air rushes in after the shock wave passes, creating a strong wind force or drag on all surfaces of the building while rolling up debris ; When the explosion occurs outside the building, part of the energy will be transferred to the ground to form a crater, and produce an instantaneous high-intensity ground shock wave.
Compared with the damage to buildings caused by earthquakes, strong winds or floods, explosions have the following distinctive features:
- Severe pressure intensity: Heavy bombs can often cause a pressure peak of more than 100 psi to buildings, which is several orders of magnitude higher than the peak pressure of natural disasters, causing major damage and failure of buildings. When the 500 lb TNT equivalent explosive is detonated, the peak pressure can reach 1,680 psi at a distance of three meters, while the 5,000 lb TNT equivalent explosive can reach a huge pressure of 3,910 psi at a distance of six meters.
- Local damage: The explosion pressure is inversely proportional to the cube of the distance, so the damage on the side of the explosion is much higher than that on the other side, and a single-sided air blast or contact explosion will cause more local damage to the building.
- Short duration: The explosion process is in milliseconds. The stress imposed on the building structure by an earthquake or a strong gust of wind is measured in seconds, and the stress imposed on a building structure by a sustained strong wind or flood is measured in hours. Although the instantaneous power of an explosion is several orders of magnitude greater than that of natural disasters, due to the extremely short duration of action, the heavier the structure of the building, the more it can mitigate the power of the explosion.
The destruction of the building is due to the uneven load on each part after the structure absorbs a large amount of energy, causing structural damage. However, because the explosion time is extremely short, the energy load disappears before the entire structure absorbs energy completely and causes damage, thereby reducing the damage. This is in contrast to earthquakes, which are usually long enough to transmit enough energy throughout a structure to produce a resonant effect that completely destroys the structure.
As in a major earthquake, some buildings completely collapsed and some remained unscathed. The degree of damage to buildings when they were bombed was related to individual buildings and the details of the explosion. structure, to estimate the extent of blast damage.
Direct air bombing and debris effects of missiles
Most of the damage from the aerial bomb explosion comes from the direct air bombing effect, and the accompanying fragmentation effect only causes weak damage. The damage caused by the blast shock wave can be subdivided into two parts: direct gas explosion effect and gradual collapse.
The direct air blast effect is the main destruction mechanism of the explosion. It instantly exerts pressure several orders of magnitude higher than the original design value on the surface of the building, destroying the wall, window and floor system, and at the same time acting in directions that were not considered in the original architectural design. above, causing significant damage to structural weaknesses.
When the explosion occurs on a lower floor, the shock wave will knock down the outer wall, but more seriously, the shock wave will push the girders and slabs of the upper floor upwards, causing the beams and floors to arch upwards, causing irresistible damage. Floor failure effects from low-floor explosions are common in bombing. The shock wave will transfer energy to the floors of the upper and lower floors in a very short time. The floors with smaller masses cannot absorb the energy and cause structural damage. In a few seconds, the partial collapse will evolve into the complete collapse of the entire floor.
Glass is often the weakest part of a building, and past incidents have shown that shards of glass can travel for kilometers in massive explosions and are the leading cause of injury in such accidents. The high-pressure air rushing in from shattered windows can cause eardrum damage and lung failure, as well as damage building components in its path, kicking up various splashes and causing impact injuries.
| damage effect | Chance of damage | Peak pressure (psi) |
|---|---|---|
| Tympanic membrane damage | injury threshold | 5 |
| 50% lethal | 15 | |
| Tympanic membrane damage | injury threshold | 5 |
| 50% lethal | 15 | |
| lung injury | injury threshold | 30 |
| 50% lethal | 80 | |
| fatal lung injury | injury threshold | 100 |
| 50% lethal | 130 | |
| 100% lethal | 200 |
▲Table 1 Pressure values of various human injuries(Source: DOD UFC 3-340-02, Structures to Resist the Effects of Accidental Explosions (2008b).)
| damage | Peak pressure (psi) |
|---|---|
| broken window glass | 0.15-0.22 |
| Some buildings were slightly damaged | 0.5-1.1 |
| Damaged metal panels | 1.1-1.8 |
| brick wall collapsing | 1.8-2.9 |
| collapse of wooden structures | >5.0 |
| Severely damaged steel structures | 4-7 |
| Reinforced reinforced concrete building severely damaged | 6-9 |
| Most types of buildings are completely destroyed | 10-12 |
▲Table 2. Pressure values required for various building damage（資料來源：Explosive Shocks In Air, Kinney & Grahm, 1985; Facility Damage and Personnel Injury from Explosive Blast, Montgomery & Ward, 1993; and The Effects of Nuclear Weapons, 3rd Edition, Glasstone & Dolan, 1977.）
Although the chance of serious injury is related to peak pressure and duration, the lung lethal threshold is approximately 100 psi pressure for three milliseconds, or approximately 25 psi pressure for 20 milliseconds. Chances of survival increase with individual weight gain, and lower-than-adult pressures can cause lung damage or death in children.
| Damage Effect Threshold | Maximum distance from explosion point |
|---|---|
| building slightly damaged | 250 meters |
| bodily injury | 100 meters |
| brick wall collapsing | 80 meters |
| lethal | 60 meters |
| Most types of buildings are completely destroyed | >30 meters |
| Concrete beam failure / building collapse | 13 meters |
▲Table 3. 1,000 pounds of TNT equivalent explosive power(Source: US Air Force. Installation Force Protection Guide.)
When the missile directly penetrates into the building and detonates, the building with larger floor area and lighter floor weight will suffer more damage; similarly, the building with larger glass window area will suffer more damage. If the missile explodes outside the building, it will cause the brick wall of the non-structural body to collapse, but it is very difficult to destroy the iron house or the reinforced concrete building. It is almost necessary to penetrate directly into the bottom of the building or explode at a very close distance to cause the partial collapse of the building.
The explosion of the missile in the narrow streets and alleys will amplify the power of the shock wave, and the narrow streets and alleys are usually dominated by old-fashioned brick apartments, which may cause the brick walls of large-scale buildings to collapse and fall. Therefore, unless the missile is hit directly or at a very short distance when the missile explodes, there is little chance of causing casualties due to the explosion shock wave.
It can be seen that most of the explosion deaths come from being buried by collapsed buildings or being hit by flying fragments, and the main cause of injury is glass fragments. Therefore, it is very important to avoid injuries through correct knowledge or actions of air defense evacuation.
