The terrible blast killed in unusual ways
by ANDRES PEREZ
On July 3, 2016, Islamic State carried out its deadliest attack ever when it employed a vehicle-borne improvised explosive device — a VBIED — against crowds of people along a busy street in Karrada, Iraq.
The attack claimed the lives of 324 innocent civilians, many of them children. More than 200 additional civilians were injured in the attack.
On July 28, the BBC released an article summarizing some key characteristics of the Karrada explosion, which set it apart from other IED attacks carried out by ISIS thus far. It seems the militants deployed a new kind of bomb.
Consider — there was no visible crater at the seat of the explosion. The explosion did not cause serious structural damage to the nearest buildings. Many witnesses report sensing extreme heat after the blast. And several experts estimate that the initial blast killed 20 to 30 people, whereas the remaining 300 were killed by secondary fires.
These characteristics are unique, because they appear to indicate that ISIS did not rely exclusively on conventional explosives for the main charge in the Karrada VBIED.
Conventional explosives versus the Karrada bomb
Conventional explosives tend to create most of their effect from a powerful, but short and sharp blast. Therefore, when conventional explosives are used in a large VBIED, the blast usually leaves a telltale crater and causes considerable structural damage to nearby buildings. Blast site images from the VBIED attacks on the Alfred P. Murrah Federal Building in the United States and Khobar Towers in Saudi Arabia are good references.
According to security experts and drone footage, however, the Karrada explosion does not seem to have created a visible crater or caused considerable structural damage to nearby buildings.
Furthermore, survivors uncharacteristically felt the effects of the initial explosion for long enough to recall it as extreme, searing heat. These facts appear to indicate a longer-lasting, more billowing type of explosion. In addition, fewer than 10 percent of the victims appear to have died from the initial blast, whereas the remaining 90 percent seem to have died in extensive secondary fires.
Therefore, when assessing the type of weapon ISIS used in Karrada, the evidence seems to point toward a powerful, long-lasting incendiary explosion.
Fuel air explosion, or FAE, weapons were designed to overcome the shortcomings of conventional explosives and are characterized by their superb incendiary effects, as well as the absence of large blast craters. They usually consist of fuel-rich gels or slurries and a “burster” that, upon detonation, disperses the fuel component as an aerosol cloud and then either ignites or detonates it.
The continual combustion of the outer layer of fuel molecules as they come into contact with the air will generate additional heat that maintains the temperature of the interior of the fireball and thus sustains the detonation. In other words, FAE weapons create a large and relatively long-lasting fireball.
As a result of these characteristics, FAE weapons initially seem to provide a plausible theory for the type of IED used in Karrada. Nevertheless, FAE weapons have another characteristic that does not fit well with the circumstances of the Karrada attack — they can be 12 to 16 times more destructive to buildings than conventional explosives are.
Therefore, a normally-operating FAE weapon would have caused much more structural damage to adjacent buildings in Karrada than appears to be the case.
Incendiary weapons are designed to spread extremely hot, slow-burning fires. While incendiary weapons use materials such as thermite, magnesium powder and white phosphorus, the most common and easy to improvise substance is arguably napalm.
Napalm is a mixture of a gelling agent and a fuel — usually gasoline — that sticks to skin and causes severe burns once ignited.
Moreover, napalm is able to flow into foxholes, bunkers and other fortifications, making it very effective against dug-in enemy personnel. Further, napalm is extremely easy to make, and recipes are readily available on the internet.
It is important to note, however, that flammable substances such as napalm are not explosives. Therefore, in the context of traditional incendiary weapons, their flammable properties are merely used to enhance the effect of conventional bombs.
This means that if ISIS manufactured a napalm IED for use as a standard incendiary weapon in Karrada, it would have likely required a main charge containing conventional explosives that would have left a telltale crater in the ground.
Accordingly, the characteristics of a standard incendiary weapon do not fully fit the circumstances of the Karrada attack, either.
Deflagration versus detonation
The answer to the mystery surrounding the Karrada IED may lie in the difference between deflagration and detonation.
When a mixture of flammable gas and air ignites, a sudden transition can take place from a deflagration type of combustion — fire and flame — to a detonation type of combustion featuring an explosion with a shock wave.
FAE weapons rely on the deflagration-to-detonation transition to produce their devastating shock waves.
Crucially, however, the transition does not always occur when FAEs are employed. According to a 1993 study on FAEs by the U.S. Defense Intelligence Agency, “if the fuel deflagrates but does not detonate, victims will be severely burned and will probably also inhale the burning fuel.”
Given the facts laid out above, it is reasonably possible that ISIS employed an FAE VBIED containing napalm that deflagrated but did not detonate. This theory seems to account for each of the unique characteristics of the attack that were set forth in the BBC’s July 28 article.
As mentioned above, FAE weapons usually do not leave a crater in the ground. An FAE weapon that only deflagrates is even less likely to leave a crater because the only shock wave at the blast seat would have been produced by the small “burster” charge. Moreover, lack of detonation within the fuel cloud could explain the absence of serious structural damage to nearby buildings.
Additionally, if an FAE weapon in Karrada only managed to deflagrate its flammable cloud, it would have produced an enormous fireball that could explain the extreme heat felt after the blast. This would especially be the case if napalm was used as the incendiary mixture because it burns at more than 5,000 degrees Fahrenheit, or around 2,760 degrees Celsius.
It is likely that ISIS would have used napalm because it is cheap, simple to produce and very lethal.
Moreover, the intense and long-lasting fireball caused by the deflagration of a large cloud of aerosolized napalm would have caused mass casualties on the crowded shopping street in Karrada.
Once the fireball subsided, the large quantities of styrofoam walls, banners, textiles and perfumes along the street would have sustained the blaze, resulting in further deaths. This would explain why approximately 90 percent of the Karrada victims were killed by fire.
ISIS relies on IEDs as a primary weapon, and is highly skilled at manufacturing a wide and sophisticated variety of them. While it depends on tried and true IED designs for much of its operations, ISIS also regularly experiments with new methods for enhancing and concealing these devices.
In July 2015, for example, the group prepared and employed improvised chemical weapons by repurposing mortar rounds to include chlorine gas. Confidential sources assert that ISIS has prepared and employed additional, albeit equally crude, variants of chemical weapons.
Accordingly, it is highly likely that ISIS would have the will and capacity to produce an FAE VBIED.