An improvised propane bomb is the most likely device used by the person behind the Christmas Day bombing in Nashville.
Nashville PD has released a high-resolution video of the explosion that can be viewed here. As a technical note, the camera may be a city camera used to monitor accidents at the intersection. The video does not offer a fast frame rate that would allow for a much closer examination of the blast.
This is video of Friday morning's explosion recorded by an MNPD camera at 2nd Ave N & Commerce St. pic.twitter.com/3vaXhoUOAR
— Metro Nashville PD (@MNPDNashville) December 28, 2020
SOFREP has viewed and analyzed several videos of the explosion and makes the following observations.
First, the explosion shows a bright fireball that evaporates very quickly and cleanly without much smoke dust or debris vaporization. This suggests that fuel, rather than explosives like C4, Dynamite, TNT, black powder, or ammonium nitrate, provided the source of the blast.
Hollywood explosions use lots of kerosine fuel, which creates big fireballs for dramatic effect, but they consume themselves and burn out very quickly. Propane creates extreme heat — on the order of 2,000 degrees Fahrenheit. It burns very cleanly with very little (even less than kerosene) smoke or residue. This is why propane is the preferred source of outdoor grills. But it is not ideal as an explosive.
We do not assess that a liquid fuel like kerosine was used because such fuels do not burn evenly at the point of ignition. What’s more, liquid fuel would have been ejected by the initial detonation of a precursor explosive and stuck to everything nearby. This would have been ignited by the heat of the initial blast setting trees, cars, brick walls, and light posts on fire. A large, raging kerosine fire of combustible material in the area of the explosion was not observed in the videos we’ve seen so far. Two cars that were damaged in the explosion caught fire and burned as a result of their combustible tires, plastics, and the fuel in their tanks.
The area of destruction seen in the available photos is fairly small. This is because propane’s shattering power (called Brisance by explosives experts) is not very high as it is with explosives like TNT or ammonium nitrate. This is supported by studies that have shown that in a propane explosion, the blast wave, even very close to the charge, is much less than a TNT explosion’s at that same close distance and with the same energy yield. In layman’s terms, when TNT and propane explode at the same energy yield the blast wave (shattering effect on near objects) is much lower for propane. This also explains why buildings, mostly made of brick, did not collapse by the explosion.
We do not see a visible crater in the explosion area. A crater often marks high explosive detonations and would be absent from a propane explosion. Again, this would be due to the much lower Brisance level of propane versus high explosives in which the blast would simultaneously drive out in all directions at great force. By contrast, in the Oklahoma City bombing, Timothy McVeigh used a moving truck with 13 barrels of ammonium nitrate and three with a mixture of ammonium nitrate and diesel fuel. In addition to causing the collapse of one-third of a federal courthouse building, the blast damaged other buildings in a four-block radius and killed 169 people. It left a crater 30ft wide and eight feet deep. The bomb cost McVeigh about $5,000 to make.
We also assess that an improvised propane bomb would be within the means and expertise of the suspect, who, it is reported, had some experience with electronics. He would be able to make an electric match with a reliable timer very easily. We will not go into speculation on how he improvised the device (for reasons that should be obvious) but we will say that 30 outdoor grill canisters inside that motor home would contain over 5,000 cubic feet of propane gas. And that seems sufficient to create the damage we have seen so far.
We should mention that these observations are made by our staff writers and sources and based on the information available at this time. They are not definitive and we will update them as further information comes to us.