is to get as far away from it as possible. Atomic bombs are based on the theory of nuclear fission, that when a large atom splits, it releases a massive amount of energy. Thermonuclear weapons, (colloquially known as "hydrogen bombs") use the energy from an initial fission explosion to create an even more powerful fusion explosion. The term "dirty bomb" refers to a specialized device that relies on a comparatively low explosive yield to scatter harmful material over a wide area. Most commonly associated with radiological or chemical materials, dirty bombs seek to kill or injure and then to deny access to a contaminated area until a thorough clean-up can be accomplished. In the case of urban settings, this clean-up may take extensive time, rendering the contaminated zone virtually uninhabitable in the interim. The power of large bombs is typically measured in kilotons (kt) or megatons of TNT (Mt). The most powerful bombs ever used in combat were the two atomic bombs dropped by the United States to attack Hiroshima and Nagasaki, and the most powerful ever tested was the Tsar Bomba. The most powerful non-nuclear bomb is Russian "Father of All Bombs" (officially Aviation Thermobaric Bomb of Increased Power (ATBIP)) followed by the United States Air Force's MOAB (officially Massive Ordnance Air Blast, or more commonly known as the "Mother of All Bombs"). Below is a list of five different types of bombs based on the fundamental explosive mechanism they employ. Compressed gas Relatively small explosions can be produced by pressurizing a container until catastrophic failure such as with a dry ice bomb. Technically, devices that create explosions of this type can not be classified as "bombs" by the definition presented at the top of this article. However, the explosions created by these devices can cause property damage, injury, or death. Flammable liquids, gasses and gas mixtures dispersed in these explosions may also ignite if exposed to a spark or flame. Low explosive The simplest and oldest bombs store energy in the form of a low explosive. Black powder is an example of a low explosive. Low explosives typically consist of a mixture of an oxidizing salt, such as potassium nitrate (saltpeter), with solid fuel, such as charcoal or aluminium powder. These compositions deflagrate upon ignition, producing hot gas. Under normal circumstances, this deflagration occurs too slowly to produce a significant pressure wave; low explosives, therefore, must generally be