What Is Different About This Explosion?

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Do you notice anything peculiar about the explosion that destroys this Honda Civic?

Watch this very brief video clip of a Honda Civic hatchback being destroyed by an explosion from within. Does something seem odd about the blast? (No, the answer is not that the skin of the passenger-side door almost destroyed my camera.)

In a moment, we’ll provide a clue, and then the real answer.

First, the background. Last week the staff and students in the United States military’s Advanced Improvised Explosive Device Disposal course participated in a bomb-disposal drill at Northwest Florida Regional Airport, on the Florida Panhandle. An account of the drill, held just days after the terrorist attack at the Boston Marathon, appeared in The New York Times on Friday.

Michael Spooneybarger for The New York Times A soldier inspected a car after a detonation.

That drill brought together military and civilian law enforcement and safety organizations - an explicit acknowledgment that in the fight to thwart makeshift bombs, the public is best served when knowledge, skills and equipment are pooled. And it is a irrefutable, if sad, fact that there is no pool of experience like the military’s veterans of explosive ordnance disposal teams in Afghanistan and Iraq, two countries where improvised bombs became the primary causes of wounds to service members, and where the bombs have been used extensively against civilians.

Almost all of the Advanced Improvised Explosive Device Disposal course, which is part of the United States Navy’s school for explosive ordnance disposal technicians, takes place in classrooms and training ranges on Eglin Air Force Base. The video at the top of this post was filmed at one of those ranges last week.

Look at the video again. Here’s the clue: Do you notice what is missing? Watch closely, because once you notice what is not present, the game is given away.

What is missing is the flame. Clearly there is a sizable blast originating somewhere near the back seat. But there is no flash and no fire. The car is blown open by pressure.

So what is happening? This explosion was a demonstration of what bomb-disposal technicians call a disrupter charge - an explosive encased within another substance. The purpose of such charges is to instantly separate the components of a bomb without causing the bomb’s main charge to explode.

There are many forms of disrupter charges, including off-the-shelf products like the BootBanger, an explosive paired to narrow drums of water, which can be placed under the trunk of a parked car, and will project the water and force upward when the charge is detonated.

One of the ideas behind such charges is that they can minimize property damage around a suspected car bomb. A comparatively small disrupter charge will destroy the suspected vehicle, but its effects on the surrounding area will be far less than if a car bomb were to explode.

In the case of the video above, the explosion was caused by a recently fielded form of disrupter charge known as a VMODS, the military’s acronym for Vehicle Modular Overpressure Disrupter System. A photograph of one of the modules is below.

C.J. Chivers/The New York Times A Vehicle Modular Overpressure Disrupter System.

The VMODS does not rely on water. It is a multidirectional charge of plastic explosive encased in a squat plastic cylinder of ABC fire-extinguisher powder. The modules can be fitted together, so that a disposal team can select the size of the blast they seek, depending on the size and composition of the area or the vehicle the technicians hope to disrupt. In this case, three modules were fitted together, for a total of a little less than two pounds of net explosive weight.

For the purposes of this demonstration, the charge was emplaced by a Marine technician, Gunnery Sergeant Pierre Anthony. But the VMODS was designed to be carried and emplaced by a Talon robot, which can shatter a car window with its robotic arm, then drop the charge into place. The VMODS is then detonated remotely, by an operator at a safe distance back.

Back to the quiz. On Thursday, I posted this video on my personal blog, and asked readers if they could spot what was peculiar about the explosion. In-house, one editor guessed it right - Greg Winter of the Foreign desk. And outside The Times, Matt Egleston, a reader, tweeted the correct answer, too. “No flame/fire?” he wrote.

@cjchivers no flame/fire?

â€" Matt Egleston (@MattEParties) 26 Apr 13

That’s exactly right, and by design - an explosive tool that can provide a safer and lighter touch when faced with one of the most treacherous problems presented by terrorism and unconventional war.