Improvised Explosive Devices

The military bomb, as we generally recognise it, is a ballistic shaped object filled with large quantities of explosive and dropped from aircraft from the air.

It is designed to explode on impact when it reaches its target. But terrorists, criminals, extortionists and anti-social elements extensively use their own types of homemade bombs, called “Improvised Explosive Devices” or “IEDs”.

As an X-ray screener you must look out for any suspicious item – and not just obviously suspicious items like guns or knives, but also anything that could be an IED.

IEDs are often difficult to identify because they are constructed by terrorists entirely to their own design.

Terrorists have used the following methods to infiltrate IEDs onto aircraft:

The Pan Am Flight 103 bombing over Lockerbie, Scotland that claimed the lives of 259 passengers and an additional 11 people on the ground was the result of an IED that contained a small amount of Semtex, an extremely powerful plastic explosive, hidden inside a cassette recorder.

Identifying IEDs with X-ray is far more difficult than detecting weapons, because explosives don’t have defined, predictable forms. They can be liquid or gas, or solid in any shape or size.


IEDs don’t generally comprise sticks of dynamite and an alarm clock (stereotypical bombs are virtually nonexistent), but often utilise plastic explosives which can be moulded into an unlimited number of innocuous/ambiguous shapes and objects – including thin sheets which terrorists have used to line bags.

The problem of spotting IEDs with x-ray is further complicated by the fact that plastic explosives have densities and characteristics which make them appear similar to many non-threat, organic materials (such as plastic, leather, rubber, paper, textiles and foodstuffs) routinely contained in carry-on baggage.

If explosives are present in a packed bag they will almost certainly be partially or completely obscured by denser innocuous objects. The design of IEDs is continually changing and evolving.

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As far as the technical aspects of constructing IEDs are concerned, terrorist devices have ranged from bombs made from normal everyday items, to highly sophisticated devices utilising digital components.

Modern terrorists who use IEDs as their weapons of choice are often extremely creative in designing and placing their weapons. Hundreds of everyday articles have in the past been modified and used to conceal an explosive or incendiary device, for example video cassette cases, vacuum flasks, toys, food, aerosol cans, sweet boxes and wrapped gifts.

Containers, bags or boxes themselves have been turned into IEDs, for example by rolling plastic explosives into sheets and placing within linings. IEDs are often concealed by terrorists within electrical or electronic items. Items, like laptop computers, hairdryers, disk-drives, radios, cameras, mobile phones, etc., have so many different components packed into a relatively small area that an IED hidden within such items can be extremely difficult for an X-ray screener to detect.


The amount of material in an IED, the type of explosive material, the manner in which the device is constructed, and the location or the type of bag in which it is placed all have a bearing on the specific destructive potential for each IED.

The destructive powers of even small IEDs can be quite devastating when experienced in close proximity, or if they explode in the pressurised passenger cabin of an aircraft flying at altitude.

A major advantage of IEDs to terrorists is that they destroy evidence and the perpetrator can be miles away when the explosion occurs. Modern terrorists are capable of producing sophisticated IEDs, remotely detonated, with highly technical movement devices and countermeasures with booby-traps built into the design.

Barometric IEDs are just one of the advanced weapons in the aviation terrorist’s arsenal. The detonator of a barometric bomb is linked to an altitude meter, causing the explosion to occur in mid-air. The Lockerbie IED had a detonator with a barometric sensor with a timer delay and triggered only after the aircraft had reached a specific altitude and flew at that altitude for a set length of time

It is important that you become familiar with the appearance of IEDs by regularly practising on a CBT training system to learn the typical X-ray signatures of their components. By being exposed to the huge library of IEDs in systems like Simfox, you can develop an awareness of the colours, densities, shapes and sizes that may suggest their presence in a packed bag.

IEDs are comprised of a few basic components, which will vary in basic appearance, but will generally always be present. The component parts of an IED are as follows:

1. The Explosive:

Explosives are chemical compounds or mixtures which on application of an external stimulus such as heat, shock, friction or ignition undergo a dramatic chemical decomposition. At the most basic level, an explosive is just something that burns or decomposes very quickly, producing a lot of heat and gas in a short amount of time. This chemical reaction results in a sudden release of large amounts of energy. When high explosives detonate, they release gases 12,000 to 15,000 times greater than their original volume and temperatures of 3000 to 4000 degrees centigrade. The gas expands faster than the speed of sound and generates a powerful shock wave. The pressure can push pieces of solid material outward at great speed, causing them to hit people or structures with a devastating effect.

The explosive charge in an IED can be military, commercial or homemade explosives – or a combination.

Types of explosives that have been used by terrorists include RDX, C4 and SEMTEX – extremely powerful military explosives, PETN, which forms the core of explosive cord fuses, TNT, Dynamite, Black Powder – which is gunpowder, Smokeless Powder – which is the propellant in pistol and rifle bullets – and also homemade Improvised Explosive Mixtures based on common ammonium nitrate fertilisers, and other readily available household ingredients like wax, oil, paraffin and sugar. Homemade explosive mixtures are often extremely volatile and can be particularly susceptible to initiation by shock, friction or heat.

Military plastic explosives are more stable, and they are extensively used by modern terrorists. The basic principal of all plastic explosives, also called plastic bonded explosives, is to combine explosives with a plastic binder material. The binder has two important jobs:

  1. It coats the explosive material, so it’s less sensitive to shock and heat. This makes it relatively safe to handle.
  2. It makes the explosive material highly malleable. It can be moulded it into different shapes to conceal it, or even change the primary direction of the explosive blast.

C4 is a relatively stable, solid explosive with a consistency similar to modelling clay – ideal for moulding into any article when constructing a camouflaged IED. When detonating, C-4 decomposes to release nitrogen and carbon oxides gasses which expand at about 8,000 meters per second, applying a huge amount of force to everything in the surrounding area.

Plastic explosives are very attractive to terrorists, as they can be moulded into an infinite number of diverse forms, including thin sheets about 5mm thick, which a terrorists have used to line suitcases, making detection extremely difficult. Plastic explosives have excellent adhesive properties – and can also be stretched into long, thin strands without breaking.

A distinguishing characteristic of many plastic explosives viewed under X-ray – except those in thin sheet form – can be their higher relative density compared with other common organic materials like paper, wood and plastics. On a dual-energy X-ray image, military and commercial explosives will be coloured “orange” – the colour for organic substances.

2. Power Supply:

Every IED needs a power supply, often using commercial batteries to trigger the initiator, known as the detonator.

In most day-to-day electronic devices that use batteries, several batteries are used together.

Similarly, a terrorist may also need several batteries to sufficiently power an IED, and may tape a cluster of batteries together which can sometimes be of different types. The battery in an IED can, however, take many shapes and forms. Batteries are generally full of carbon, with a metal casing. The carbon in batteries is organic, but because batteries are so dense and encased by metal, they will generally appear as blue or green on the X-ray screen, rather than the usual colour for organic material, which is orange.

Power sources are often the most visible components of an IED.

Look out for:

3. Initiator

Most explosives need the application of a small explosion in an initiator, know as a detonator, to produce sufficient energy to trigger the secondary and/or main charge. Detonators should be regarded as explosive devices in their own right.

There are basically two kinds of detonators, ‘Plain’ and ‘Electrical’. Both types are made from a copper, glass or aluminium tube, closed at one end. Detonators are generally extremely delicate structures, about 6mm diameter and 25 to 150mm in length. An electrical detonator uses a brief electric charge to set off small amounts of explosive material in the centre and tip of the detonator.

Owing to their small size and relative lack of density, detonators can be difficult to detect. However, there are some clues which can help you to spot detonators in items you screen:

4. Switch:

A switch can either be a complex electronic component, or as simple as two intersecting loops of wire. Switches are IED initiating mechanisms normally based on several types: Anti-handling switches are designed to activate when the IED is lifted, moved, opened or disturbed. Delay switches time the explosion by clockwork, digital, thermal, chemical or electro-chemical mechanisms. Switches can also detonate a device by remote control.

A switch can be just one tiny component of a well-disguised IED, but switches can often be identified if you ask yourself “Should this item contain any metalic components?” For example, a packet of biscuits should not have any metal displayed, nor should a box of chocolates.

5. Wiring:

Wiring is required to combine the components of an IED. Terrorists will often use various lengths of wire, without concerning themselves with the appearance of the item. The quality of the wiring may be inconsistent with the quality of the item. Or there could be an excessive amounts of wiring for the size of the article. Wires could even be protruding from the item. This can give you valuable clues that an electrical or electronic item has been tampered with.

6. Timer/Delay Mechanism:

The simplest delay mechanism is the slow-burning fuse. The use of mechanical clocks and wristwatches is also a common and effective method of delayed detonation in terroist devices. The basic idea of clocks and wristwatches is to use the rotating hands to complete an electrical circuit and detonate the bomb. Digital and electronic timers are also often used by today’s sophisticated terrorists.

Identifying IEDs

IEDs are normally not seen at checkpoints and without specialised training they will inevitably be rather difficult to identify. Screeners must recognise IED components that are cunningly concealed or disguised as innocuous items, such as liquids within bottles and containers. Poor or inconsistent craftsmanship, or unusual components, in relation to any item, especially electrical or electronic, should always be cause for suspicion. “Context” is very important in identifying IEDs. If an organic mass is present in a bag with wires and batteries with something electrical or mechanical, this could indicate that an IED is contained therein.

You should be alert for suspicious people as well as suspicious items when working at your checkpoint. Terrorists are very cunning in concealing their IEDs. (In the well-publicised “Shoe Bomber” incident a terrorist called Richard Reid attempted to detonate explosives during an American Airlines flight from Paris to Miami. The heel of his training shoe was packed with explosive. Investigators later built a copy of the Shoe Bomber’s IED and exploded it. They say that had the device exploded on the aircraft, it would have blown a large hole into the fuselage and knocked the plane out of the sky, probably killing all on board). You should, therefore, always look at the person as well as the bags and packages he/she presents. If you are suspicious, select him/her for additional screening. X-ray technology works best when used in conjunction with operators that actively assess passengers and adapt security techniques accordingly. Using such techniques, you can enhance security AND increase passenger throughput. IEDs are so difficult to detect with X-ray that we need to use every technique to help us to find them.

Other Types of Explosive Devices & IED Components

Pipe bombs

Pipe bombs are one of the most common type of terrorist bomb. Steel, iron, aluminum or copper pipes that are widely available are used and low-velocity explosives are tightly capped inside.

The stronger the pipe, the better it can contain the explosion before rupturing, and therefore the more powerful the blast. The final rupturing of the pipe casing, on detonation, massively intensifies the blast effect. High explosives could, of course, be used in a pipe-bomb but in this case the pipe would probably only function only as a fragmentation jacket and play no part in containing the blast. A pipe-bomb is a lethal and inherently unstable device. Always be on the look out for lengths of metal piping in baggage or packages. Terrorists have recently produced non-metallic pipe bombs, designed to successfully pass through arch metal detectors. PVC pipe is used as the pipe body, and plastic end caps are fastened on the ends with PVC cement, with glass fragments taped to the pipe body to increase lethality. These non-metallic pipe-bombs are not be as powerful or destructive as their metal counterparts because the PVC pipes cannot contain the explosive gasses as long as metal pipes can, but they are capable of inflicting lethal wounds within several metres blast radius. Therefore also be aware of the possibility of coming across a non-metallic pipe-bomb device.


Terrorists sometimes include shrapnel – which is metal items such as nails, nuts and bolts, steel ball-bearings, etc. – in their IEDs to cause greater injuries to victims. In an explosion this shrapnel can travel up to a speed of 6000 km per hour, inflicting horrific injuries. Any container of small metallic objects in a bag should always arouse suspicion.

Anti-personnel mines

Few military “bombs” would be of a size suitable for concealing in baggage for use in terrorist attacks. The exception to this generalisation is the anti-personnel mine. These mines have often been adapted by terrorists into IEDs. Anti-personnel mines can be constructed of combinations of metal, composite plastics, ceramic and glass. Metal balls or glass fragments are often included in these mines to cause greater injuries to victims. More than 350 different kinds of anti-personnel mines have been produced by more than 50 countries. They can be as small as a packet of cigarettes, weighing as little as 50 grams. Always be extremely wary of any small, dense disk, ball or cube which may be an anti-personnel mine.


There now exists a real threat that a Chemical, Biological or Radiological agent could even be included into a terrorist IED to add to the destructive power and psychological effect of the device.


A Vehicle Borne IED (VBIED) is a car bomb or truck bomb. VBIEDs are popular with assassins, terrorists and insurgents and have been used to kill and maim, as well as to cause damage to buildings and other property. Their popularity rests largely in the fact that they act as their own delivery mechanism, can carry a large amount of explosive and, because of the sheer volume of vehicles on the road, attract very little suspicion. Additionally, due to their popularity, there is a vast body of international know-how and expertise within the criminal and terrorist communities on how to construct effective VBIEDs.

There are two basic types of VBIEDs: suicide (where the vehicle is moving) and stationary (where the vehicle is parked). VBIEDs can be made in advance at a safe location some distance from the target. The explosive may be in the load-carrying area of the vehicle, concealed in the chassis or behind panels, or in one or more containers such as a beer kegs, dustbins or wheelie bins. Sometimes bags of nails or other shrapnell are placed in the vehicle, to help maximise casualties. VBIEDs will create additional shrapnel through the destruction of the vehicle itself, as well as using vehicle fuel as an incendiary weapon.

A Large Vehicle-Borne Improvised Explosive Device (LVBIED) is a heavy lorry filled with explosives. These vehicles enable terrorists to carry very large amounts of explosives, possibly several tonnes, to a target and cause casualties and destruction over a range of hundreds of metres. Timothy McVeigh, who carried out the Oklahoma City bombing in 1995, killing 168 people, used a cargo vehicle packed with a large quantity of improvised, fertilizer-based explosive.

An under vehicle improvised explosive device (UVIED) is a type of small, ‘booby-trap’ improvised explosive device placed in, on, or under a vehicle, and designed to explode when the vehicle moves.

VBIEDs and roadside bombs may be partially comprised of military ordinance, such as an artillery or mortar rounds, attached to a detonating mechanism.

Potential VBIED indicators include:

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