Ammonium nitrate is very hyroscopic and must be kept dry to maintain its effectiveness as a component of explosives. Those bags of AN shown in the pictures of the pre-blast warehouse are
anything but air tight.
You can readily see the moisture content in the air as the blast wave blows outward from the explosion. It is what created the hazy fog during the initial few seconds. As the blast wave moves out and away the air becomes clear revealing the debris cloud.
Too, for there to have been an AN explosion only the fertilizer would have to have been stored under pressure. By the pictures shown it clearly wasn’t. It was stored in dense, woven material like tyvek or nylon bags in an open warehouse at the mercy of ambient temperature and humidity conditions.
As you quote “ammonium nitrate/fuel oil” can detonate in a pressure sensitive burn which is ANFO not straight AN. ANFO does not have the brisance of a high order explosive such as RDX, Semtex, or the ever popular C4. It’s good for blasting stumps, mild rock such as slate or shale but it cannot create a blast or pressure wave that traveled as fast, or was as destructive for such long distances, as what is shown in all the videos. There was something else being stored there in that warehouse and the Lebanese are using the AN story as a cover.
All the above is true for stump charges and truck bombs.
Not for ships and building on fire and loaded with thousands of tons of ammonium nitrate. The huge explosions on ships in Halifax and Texas City and in railroad cars did not have the ammonium nitrate under pressure. Nor I believe any special detonators.
Fire raises the ease of detonation for ammonium nitrate as the temperature increases.
The formula for explosive decomposition is 2NH4NO3 → 2N2 + O2 + 4H2O
Plenty of vaporized water produced, plus the explosion happened on the water front, also plenty of water.
The expanding white bubble was the shock wave causing condensation in the air. It quickly dissipates.
The detonation velocity of ammonium nitrate with a density near 0.8 is around 10,000 feet per second. Ammonium nitrate with a density near 1.2 may have a velocity of 15,000 feet per second. It's not the highest order explosive, but it is still classified as a high explosive.
It also makes a cold pack when the ampule inside the plastic pouch is crushed and the ammonium nitrate mixes with water.
You can make it at home with commonly available materials but it is difficult.
Ammonium Nitrate in fertilizer in the US is no longer useful to make explosives due to impurities added to it to make it virtually non explosive.
Here is an article that describes the observable effects of the explosion.
Here’s what the videos of the Beirut blast tell us about the explosion
By
Alex Horton
August 4, 2020 at 7:35 p.m. EDT
The massive explosions in a Beirut port on Tuesday provoked fear, then speculation after an eerie, white cloud enveloped the lenses of bystander videos, with many
suggesting online that it looked something like a nuclear blast.
But the building consensus among arms experts and Lebanese officials is that the
explosion, which killed at least 63 people and injured thousands more, may have been ignited by burning chemicals stored at a warehouse.
Many not accustomed to seeing large explosions may conflate mushroom clouds and spherical blast waves as nuclear, said Jeffrey Lewis, an arms-control expert and professor at Middlebury Institute of International Studies at Monterey. “But some of the things we associate with nuclear explosions are just associated with explosions.”
Maybe the first
#Beirut explosion was fireworks. The second...
pic.twitter.com/RPapULgIMi
— Cᴀʟɪʙʀᴇ Oʙsᴄᴜʀᴀ (@CalibreObscura)
August 4, 2020
Few things can be concluded from the videos, including some filmed before the bigger of the blasts, which Lewis said may have begun when munitions in storage caught fire.
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A rising cloud of white smoke featured crackling and bright pops consistent with when small munitions — rockets, for instance — begin cooking off, he said.
Then a fireball erupts, followed by an orb of white that quickly expands from the blast zone. That is the pressure of the shock wave condensing the moisture in the air, he said.
Brian Castner, a former Air Force bomb technician and investigator at Amnesty International, echoed that on Twitter, saying the shock wave “is visible in the humid air.”
Lebanese Interior Minister Mohammed Fahmi said it appeared that stocks of ammonium nitrate, a fertilizer that can be used in bombmaking, had exploded.
T
he telltale signs of ignited ammonium — reddish smoke — spewed from the blast, Lewis said. The color is consistent with the chemical compound and comes from nitrogen oxides, the byproduct of which gives smog its reddish-brown tones.
Stunning video shows explosions just minutes ago at Beirut port
pic.twitter.com/ZjltF0VcTr
— Borzou Daragahi (@borzou)
August 4, 2020
Lebanese Prime Minister Hassan Diab linked the explosions to dangerous stocks of chemicals that had been stored at the port since 2014, despite warnings from port officials that the material was not safe.
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“I promise you that this catastrophe will not pass without accountability. … Those responsible will pay the price,” he said in a televised speech. “Facts about this dangerous warehouse that has been there since 2014 will be announced and I will not preempt the investigations.”
Around 2,700 tons were stockpiled, Lebanese President Michel Aoun
said. That is near back-of-the-envelope estimates of the size of the explosion, which is around the equivalent of a “few hundred tons of TNT,” Lewis said. Ammonium nitrate is not as powerful as TNT.
In 2011, a similar explosion occurred in Cyprus after munitions
stored there for years exploded, killing at least 12.