Edit 8/05 1:40 p.m., to include the fireworks theory, of which I am skeptical. Read down.
If you’re a chemist, you are probably already familiar with the content of these papers:
- The mechanism of the spontaneous detonation of ammonium nitrate in reactive grounds.
- A Russian paper: Spontaneous explosion of ammonium nitrate in a contact with an active clorine-containing organic substance. (spelling not corrected)
- Thermal Decomposition of Ammonium Nitrate Based Composites.
The papers indicate that ammonium nitrate can do many things, and not all of them have been exhaustively studied.
This is for the nontechnical reader. Ammonium nitrate is not burnable. It acts to oxidize something else, meaning to burn it by supplying oxygen. The CNN video has clues:
- The orange color of the initial reddish-brown plume is typical of nitrogen dioxide, (NO2) which gives color to smog, It is produced by decomposition of ammonium nitrate mixed with not-enough of another substance to be oxidized. This is the trigger explosion.
- The white “dome” that appears a second after the plume is composed of water vapor and N2O, nitrous oxide, also known as “laughing gas”. This is decomposition of pure ammonium nitrate, without oxidizing another substance.
The video suggests an initial trigger reaction that caused the subsequent explosive decomposition of the bulk of ammonium nitrate at the site. The orange plume of nitrogen dioxide, left-over oxidizer, indicates that the ammonium nitrate was not mixed in correct stoichiometric ratio for an explosion. Hence, if terrorism was involved, the explosion was accidental.
In pure form, ammonium nitrate is not explosive, except for spontaneous decomposition in the event that it is heated to greater than 170C = 338F. When used to make an explosive mixture, it serves as the oxidizer, mixed with something combustible, like fuel oil. Lacking signs of combustion, such as orange glow, an infrared pulse, or flames, the white dome in the video goes against this. The white dome resulted from decomposition of pure ammonium nitrate, triggered by an actual explosion.
The official explanation is that fireworks provided the trigger. This is not an explanation, though it could be part of one. Have a look at (Wikipedia) Ammonium nitrate disasters. All of them involve one or more of
- industrial processes, where intimate mixing of ammonium nitrate with other substances has occurred
- High explosive trigger. Fireworks are not high explosives.
- Accidental intimate mixing of hazardous materials.
- Confinement in a container that concentrates heat and pressure, such as fire in the hold of a ship.
What fireworks can and cannot do:
- Fireworks are not high explosives; they are low explosives. They do not detonate to produce supersonic shock waves. Fireworks contain black powder, which just burns rapidly, in deflagration. This rules out one mechanism. Although ammonium nitrate can be detonated by a supersonic shock wave, fireworks do not produce them.
- Ammonium nitrate usually survives intense fires, unless confined in a hard container and heated for for some time. But in the video, everything happens in a few seconds.
- Perhaps for these reasons, the fireworks theory lacks support in the literature. Fireworks would be the lowest energy addition to the Wikipedia disaster list.
- Fireworks could ignite a bomb under construction.
The Russian paper suggests that in an explosion in France, broken bags became mixed with a modern disinfectant containing chlorine. This creates a complete explosive, oxidizer + something combustible. The size of the initial orange plume suggests the rare trigger powerful enough to cause the bulk ammonium nitrate to explode.
For the chemical detective, there is a natural question. In the initial explosion, what material mixed with the ammonium nitrate to produce the orange nitrogen dioxide plume? Was somebody trying surreptitiously to make something useful to someone?
- Ammonium nitrate/fuel oil is a terror favorite for large projects. The explosion could have been a bomb maker’s accident. The port was a convenient place to make car bombs since the ammonium nitrate was already there. The fuel oil to make bombs is easily sourced within the port. The colored plume suggests bombs under construction. A complete bomb would have a cleaner burn.
- For the sake of completeness, broken bags accidentally mixed with a common household/industrial cleaner, in the course of some illicit manufacturing enterprise.
- The official theory, initiation by fireworks, is inconsistent with known ammonium nitrate disasters. This is not the same as impossible.
Lebanon is governed in a power sharing arrangement that includes groups known for bomb making. An explanation that implicates them, such as bomb construction, is politically unacceptable. A politically acceptable fireworks theory, which lacks support in literature or experiment, can easily be sold to the public by confusion of low explosives with high explosives.
With Beirut’s history, the bomb maker’s factory is more attractive.