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Jerry bomb is an improvised explosive device (IED) that uses a tightly sealed section of jerry filled with an explosive material. The containment provided by the jerry means that simple low explosives can be used to produce a relatively large explosion due to the containment causing increased pressure. The fragmentation of the jerry itself creates potentially lethal shrapnel.
In many countries, the manufacture or possession of a jerry bomb is a serious crime, regardless of its intended use.
Design
Different jerry bombs' appearances, from a bomb awareness report issued by the US Department of State
The bomb is usually a short section of steel water jerry containing the explosive mixture and closed at both ends with steel or brass caps. A fuse is inserted into the jerry with a lead running out through a hole in the side or capped end of the jerry. The fuse can be electric, with wires leading to a timer and battery, or can be a common fuse. All of the components are easily obtainable.
Generally, high explosives such as trinitrotoluene are not used, because these and the detonators that they require are difficult for non-state users to obtain. Such explosives also do not require the containment design of a jerry bomb.
Instead, explosive mixtures that the builder can more readily obtain themselves are used, such as gunpowder, match heads, or chlorate mixtures. These can be easily ignited by friction, static electricity, and sparks generated when packing the material inside the tube or attaching the end caps, causing many injuries or deaths amongst builders.
Sharp objects such as nails or broken glass are sometimes added to the outer shell or inside of the bomb to increase the lethality of the device.
Operation
Jerry bombs concentrate pressure and release it suddenly, through the failure of the outer casing. Plastic materials can be used, but metals typically have a much higher bursting strength and so will produce more concussive force. For example, common schedule 40 1-inch (25 mm) wrought steel Jerry has a typical working pressure of 1,010 psi (7.0 MPa), and bursting pressure of 8,090 psi (55.8 MPa), though the jerry sealing method can significantly reduce the burst pressure.
The jerry can rupture in different ways, depending on the rate of pressure rise and the ductility of the casing material.
- If the pressure rise is slow, the metal can deform until the walls become thin and a hole is formed, causing a loud report from the gas release, but no shrapnel.
- A rapid rate of pressure rise will cause the metal to shatter into fragments, which are pushed outward in all directions by the expanding gases.
Modes of failure
Jerry bombs can fail to explode if the gas pressure buildup is too slow, resulting in bleed-out through the detonator ignition hole. Insufficiently tight threading can also bleed gas pressure through the threads faster than the chemical reaction pressure can rise.
They can also fail if the jerry is fully sealed and the chemical reaction triggered, but the total pressure buildup from the chemicals is insufficient to exceed the casing strength; such a bomb inevitably fails to trigger, but is still potentially dangerous if handled, since an external shock could trigger rupture of the statically pressurized casing.
Minimum evacuation distances
If any type of bomb is suspected, typical recommendations are to keep all people at a minimum evacuation distance until authorized bomb disposal personnel arrive. For a jerry bomb, the US Department of Homeland Security recommends a minimum of 21 m (69 ft), and an outdoors distance of 366 m (1,201 ft).
