Weapons of the Boston bombers

A shattered lid from a 6 liter pressure cooker. Image: FBI

A shattered lid from a 6 liter pressure cooker. This was part of one of the finish line bombs. Image: FBI

We started a small fire in comments with our early criticism of the police — a criticism that cop readers argue is based on misunderstanding what they should be doing in the immediate aftermath of a bomb — and have come around to have a great deal of respect for what the law has accomplished. While we were tied up in that, others on the net began to figure out what went bang.

Joe Huffman, who we’re told has amateur experience with pyro and deflagration (black powder, Tannerite), thinks its a low explosive/homemade explosive, or a deflagration. We’ll try to restate his basic argument in a couple of lines before giving you the whole thing: the duration of flame means that the combustion time was measured in seconds, not milliseconds; therefore the bomb was not made of a stoichiometric mixture (one that contains fuel and oxidant in perfect measure), as it would be if it were pro explosive. His argument in full:

See all that flame? And it looks as if there is still fuel burning in the cloud two seconds after the explosion.

I’m almost certain that no commercial or military explosive produces that much flame. Something like that would be totally banned in the mining industry.

That may mean there was a great excess of fuel in the explosive composition. Boomerite has an excess of oxygen which makes for easier detonation. Maximum power comes from a balance of oxygen and fuel. Some explosives are naturally oxygen or fuel rich. For example TNT is fuel rich. During WW II they would add ammonium nitrate which is (under the proper conditions) an explosive that is oxygen rich. The excess oxygen in the AN increased the power of the detonation by consuming the excess fuel of the TNT.

With that much flame persisting that long after the explosion occurred means huge amounts of power was wasted in light and relatively slowly expanding gases. This was not a military grade explosive. Getting the most bang for the least weight is worth the cost of getting the oxygen balance right.

This means it’s a homemade explosive.

Another possibility is that it wasn’t really a detonation at all but rather a deflagration. For example gun powders typically do not detonate. They “just” burn very rapidly. The flash you see at the muzzle of your gun at night (and sometimes even in bright sunlight) is composed mostly of burning particles of gunpowder. Confine the powder in a strong closed container, such as a pipe, and you get an explosion when the container bursts.

via Boston explosives | The View From North Central Idaho.

Joe’s argument is based on the only evidence he then had, the videos and photos; he didn’t have the images of pressure cooker parts, which of course comport well with his theory. Our experience of HE is that there is flame involved (especially the newer, less practical variants with ATF-approved taggants), but it’s momentary. However, cameras and videos can exaggerate the amount and duration of the flame.

Still, take on board Joe’s suggestion that it might have been a deflagrant (like black powder), and note the investigational development that says the bombs were contained in pressure cookers. That would be the perfect pressure vessel to contain a deflagrant until overpressure burst the vessel, turning its parts into shrapnel. This is a widely used jihadi weapon; as we’ll get to, it’s a signature of certain terrorist groups, but all these guys share their information widely, and this type of bomb has been widely reported in both jihadi and Western press, so based on the bomb alone couldn’t rule out individuals stricken with sudden jihad sole-practitioner syndrome, or a non-moslem copycat.

Joe updated his post with a link to this analysis by Rick Boatright, which confirms based on calculated flame-front speeds that the bomb was a low order deflagration, ratherthan a detonation.

So, in 0.02 seconds, the flame front expanded about 10 feet, or about 500 feet per second (340 MPH). The speed of sound in air is about 1100 feet per second, so this is a sub-sonic deflagration not a detonation. (It’s still a bomb, and still an explosion but the stuff making the bomb BURNED andd the wave-front of the burning moved out through the explosive at less than the speed of sound. It was very fast, but it didn’t go off all at once.)

So, this is the result of a “low explosive.” High explosives detonate at 3 to 9 kilometers per second and produce sonic or super-sonic wave fronts.

In terms of being an “IED” and being a “terrorist improvised explosive” the bomb was probably -not- TATP for two reasons: TATP is a high-explosive, so it would have gone off all at once, rather than burning for many hundredths of seconds. In the New York Times You-tube video cited above, flame can still be seen in the cloud from the explosion until timestamp 70.5. – the combustion continued from 69.7 to 70.5, almost eight tenths of a second. That’s burning, not detonation.

More thorough versions of these calculations will be done by the FBI bomb experts investigating the blasts. Several witnesses commented on a “gunpowder smell” or “fireworks smell” but none of them distinguished between the smell of smokeless and black powder, at least as far as we have read. Black powder is far more likely to be involved — it’s more widely available, and superior to any smokeless powder for this purpose. It’s also homemade relatively simply, although homemade black powder will be weak compared to that commercially available.

The Pressure Cooker Bomb

Other pressure cooker (and containing bag) remains of the bomb planted by Tamerlan Tsarnayev. FBI.

Other pressure cooker (and containing bag) remains of the bomb planted by Tamerlan Tsarnayev. FBI.

The bombs used at the Marathon, and the bomb thrown at police during the Friday night firefight, were pressure cooker bombs. The bombs appear at first glance to be identical, having had a simple timer, a homemade explosive or deflagrant filling, all packed into a six-liter pressure cooker inside a nylon duffle bag or backpack. Components of all of these, including one largely intact pressure-cooker lid, were recovered from the scene of the blasts. The lid was found on a roof across the street from the blast.

Pressure cooker bomb from Inspire Magazine. Click to embiggen.

Pressure cooker bomb how-to from Inspire Magazine, July 2010. Click to embiggen.

The pressure cooker, of course, is the ideal pressure vessel for a bomb loaded with a deflagrant rather than a high explosive. Here’s the DHS warning of pressure-cooker bombs in 2010, and here’s the a large .pdf of the July 2010 Inspire magazine (Al-Qaeda’s magazine for would-be members with Sudden Jihad Syndrome) that describes how to make such a bomb. This link will take you to all issues of Inspire in captivity.

This kind of bomb is very widely used in Southwest Asia, especially in Afghanistan, Pakistan and Kashmir. It was in the mid-oughts a signature of Pakistani bomb-makers and their trainees, and is often used by the TTP and by various ISI-sponsored terrorists in Kashmir. In that part of the world, pressure cookers are more common than in the USA (more of our homes have ranges with burners and ovens). But successful jihad approaches are quickly disseminated by AQ’s and other jihadi groups’ internet propaganda machines — Inspire magazine being a perfect example of the methodology.

The pressure cooker bomb has been employed in the United States before. It was used in the Times Square, NYC bombing attempt. with consumer firecrackers as the explosive filling. That bomb failed. The individual who planted that bomb was Pakistani-trained.

The pressure cookers were filled with a deflagrating charge, as we’ve discussed, almost certainly black powder, and shrapnel (nails and ball bearings or BBs). The source of the powder in the bombs is, at this time, unknown. FBI bomb experts are leading the investigation into this part of the case.

What about the guns?

The investigators are being mum about the guns employed by the bombers, but at least three guns have been recovered: one with the corpse of Tamerlan Tsarnayev at the Friday night shootout scene, and two in the boat-bilge rathole into which  Dzhokar wormed himself. At least one of the guns had crudely defaced serial numbers, but investigators are confident they can recover the number and trace the guns as far as they went in lawful commerce. But the guns were not lawfully sold to, or possessed by, the Tsarnayevs. Under Massachusetts’s strict gun laws, they could not have bought them legally. (This is not a novelty. In the state. About 200 murders take place a year, and about 200 of them are committed with stolen or black-market guns. It is extremely rare for a legally-owned gun to be involved).

A Massachusetts State Police source informs us that neither Tsarnaev brother had a license to carry, which is required in the Bay State to purchase pistols and so-called “assault rifles” legally. (There are different “classes” of LTC for different purposes. All are de facto “may issue” permits, and municipalities have unfettered discretion and may interpose any additional requirements that amuse them). Dzhokar would have been ineligible for such a permit because he was not yet 21. Tamerlan would not have been eligible because he was a legal permanent resident, not a citizen. (Disarmament of legal aliens has been overturned by Supreme Court precedent, but the law has gone unchallenged in MA). In any event, the city where they lived, Cambridge, prides itself on not issuing permits, except to the wealthy and politically connected.

So the good news is: if the Feds utterly botch their prosecution of Dzhokar, he can still get the mandatory two years per gun for possession in Mass. However, the state normally does not enforce this law against violent criminals, only against otherwise law-abiding citizens who break the  malum prohibitum gun possession law alone, and somehow offended police, politicians, or other officials.

Their most probable sources are the criminal black market, first, and secondly, associates at the extremist mosque that both attended and that is a key to their radicalization, the Islamic Society of Boston’s satellite mosque in Cambridge. The ISB is a wahhabi/Muslim Brotherhood group; it’s directly controlled by the Muslim American Society, the overt arm of the Ikhwan al-Muslimeen or Muslim Brotherhood in America. The Brotherhood’s founder Sayyid Qutb is also the father of Sunni extremist terrorism and inspired Hamas and al-Qaeda. Under the circumstances, the very liberal governor of Massachusetts, Deval Patrick, retracted an unwise invitation to an ISB imam to officiate at a memorial service for the victims of his adherents’ violence — the indirect victims of his own murderous message.

Things Investigators are Learning

A bomb contains many signatures. Bombers do what has worked for them before. Even a detonated bomb leaves clues by which it can be reconstructred. (The FBI has been reconstructing bombs used on airplanes from 1956 to Pan Am 103, despite what looks to a layman like the complete destruction of all evidence. The PA 103 reconstruction was a model of scientific assistance to law enforcement and intelligence). Different explosives affect metal, concrete, glass and human victims in distinct and distinguishable ways. These are a bomber’s tracks, as distinct to a bomb expert as animal sign to an Indian tracker in a James Fenimore Cooper novel. And the timer, if any, and detonator, are also extremely strong indicators a to the source and purpose of the bomb.

The Last Word

We’re seeing a lot of bending over backwards to See No Evil in this case. But the evil is there for all to see. We know who did it. We know how they did it. And we know, despite all the posturing and hand-wringing, why they did it. We don’t know all the details and we haven’t seen all the facts, and we don’t know who all the enablers were.

We do know enough to make those who tried, thanks to wishful thinking, to hang this on their political opponents and (in the case of media types like Wolf Blitzer) their critics. Wolf, just because we think you stink at delivering the news doesn’t mean we want to blow random people up. We don’t even want to blow you up. If somebody was to blow you up, or anyone else for that matter, the percentages argue pretty strongly for someone who attends worship services on Fridays that involve banging his forehead on the ground.

Not all moslems are terrorists. And not all terrorists are moslems. But if you bet the percentages, that’s the square to put your chips on, every time. Or you could do something really radical and wait for the evidence to come in. The irony is that the media rushed to judgment, until the evidence came in refuting their judgment, and now they are anxious to give the actual perps the benefit of the doubt.

Follow the evidence where it leads. Hang the guilty. Leave the innocent alone. Those concepts used to be enshrined in our laws and culture.