How bomb blasts work
A bomb is basically some type of casing or shell that contains explosive material. The casing can be anything from a steel-walled artillery shell to a glass bottle or a sealed-shut length of lead pipe. It can even be as ordinary as a coffee tin or an automobile. Once the casing is penetrated by the force of the explosion, it will fragment outward, each piece of the shell serving as a deadly projectile. The explosive material inside the shell could be any type of high explosive, be it TNT or Semtex.
A bomb causes damage in several different ways, depending on the point at which the explosion impacts. These different points include the blast wave, shock waves, fragmentation, heat and the blast wind.
• Blast wave: When a bomb explodes, the area around the explosion becomes overpressurized, resulting in highly compressed air particles that travel faster than the speed of sound. This wave will dissipate over time and distance and will exist only for a matter of milliseconds. This initial blast wave inflicts the most damage. When this blast wave reaches a structure or person, two things will initially happen. First, the person will feel the force of the blast, which is the primary and initial impact of the shockwave. This will damage a structure or body on impact.
• Shockwaves: After a blast wave strikes a surface or body, high-velocity shockwaves, or stress waves, will continue to pass through -- in the body, they travel through the organs and tissues. Shockwaves carry energy through the medium they pass through; they're supersonic and transport more energy than sound waves. Currently, there are no effective ways to prevent shockwaves from passing through protective clothing, and in some cases protective measures may even amplify the destructive effects.
• Fragmentation: When the bomb explodes, the bomb casing, as well as any additional shrapnel (nails, screws or other items included in the bomb), will be violently thrown outward and away from the explosion. When these fragments strike buildings, concrete, masonry, glass and even people, they may fragment even further -- and cause even more damage. This is known as secondary fragmentation.
• Fire and heat: The explosion may also create a fireball and high temperatures, which will result in burns on a human body or even cause secondary fires or explosions, depending on whether any other fuel sources or flammable materials are located near the blast.
Blast wind: At the explosion site, a vacuum is created by the rapid outward movement of the blast. This vacuum will almost immediately refill itself with the surrounding atmosphere. This creates a very strong pull on any nearby person or structural surface after the initial push effect of the blast has been delivered. As this void is refilled, it creates a high-intensity wind that causes fragmented objects, glass and debris to be drawn back in toward the source of the explosion.
Source: howstuffswork.com
