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Characteristics of self explosion glass
*Starting point of breakage: Self explosion glass usually has a clear starting point of breakage, which is usually caused by defects such as nickel sulfide (NiS) impurities inside the glass. The glass fragments at the starting point are distributed radially, spreading outwards from this central position like a spider web. The fragments in the central position are relatively small, and the fragments become larger as they move towards the edges. For example, when tempered glass used in construction self destructs, a broken center resembling a butterfly wing shape with symmetrical textures on both sides can often be seen.
*Fragment shape: The glass fragments after self explosion are relatively small and evenly sized. This is because tempered glass undergoes special heat treatment during the production process, which creates pre stress inside. Once it explodes, it will break into many small pieces. These small pieces usually do not have sharp edges, but are mostly obtuse in shape, in order to reduce the risk of injury to the human body after glass breakage.
*No external impact marks: If it is a self explosion, the glass surface usually does not have obvious external impact marks, such as dents, scratches, etc., before breaking. Of course, in rare cases, glass may self destruct due to internal defects under slight external forces, but the traces of such external forces are often not obvious.
Characteristics of destroyed glass
*Broken points and traces: If it is man-made damage, the starting point of glass breakage is usually the location of external force. For example, the location hit by a stone or the place struck by a stick. This location may have obvious dents, scratches, or other signs of damage. Moreover, the distribution of fragmentation points is relatively random, unlike self explosions which have a relatively fixed center position.
*Uneven fragments: Glass fragments that have been artificially damaged have uneven sizes and shapes. The fragments around the impact point may be smaller, while those far away from the impact point may be larger. And the fragments may have sharp edges, because external forces did not cause the glass to break evenly like a self explosion. For example, when breaking glass with a hammer, the glass near the hammer's impact will break into many small fragments, while the edge of the glass may only have some cracks, and the fragments are relatively large.
*There may be traces of external tools: there may be traces of destructive tools left on the surface of the glass. If a sharp object (such as a nail) is used to pierce glass, it may leave a small hole or scratch on the glass; If a blunt object (such as a brick) is used to break glass, there will be a large area of broken marks and pits, and there may be some tool residue on the glass fragments or window frames, such as powder from the brick.
On site environment of self explosion situation
There are no suspicious objects around, such as stones, sticks, or other tools that may be used to break glass. And if it is inside a building, there is usually no human activity or other signs that could cause the glass to break around the self destructing glass. For example, when the tempered glass partition in the room self destructs, nearby furniture or other items that have not been moved can indicate the presence of external forces.
In the case of glass self explosion, the surrounding structures such as window frames are generally not deformed or damaged. Because self explosion is mainly caused by problems inside the glass, it usually does not cause significant external impact on the surrounding frame structure.
Destroyed Glass on-site Environment
Tools used to break glass may be found on site. For example, at the scene where the window glass is damaged, stones, hammers, and other items may be found in nearby grass, corners of walls, or indoor floors. And there may be some signs of disturbance in the surrounding environment, such as glass shards being swept open or moving on the ground, which may be done by the saboteurs to cover up their actions.
If someone breaks the glass from the outside and enters the room, they may also leave footprints, handprints, or climbing marks on the window frame or walls around the window.
