Properly mixed ANFO doesn't contain a huge amount of FO; ideally it's supposed to be 6% by mass. Good enough for a quick HN estimate, although I'd hope an actual after action report does better. A better calculation is that 2750 tonnes of AN would yield 2864 tonnes of ANFO, which is 2,291 tonnes of TNT equivalent.
However, we know that the explosion wasn't stoichiometrically perfect, because of the brown NO2 clouds that were hanging over Beirut. Properly mixed ANFO should release only H2O, CO2, and N2. So we know that there was some level of explosive power that wasn't fully consumed. This is why I put the ANFO yield as the absolute theoretical max, I think in reality the actual yield was much much lower.
Some other people have speculated that the fireworks like mini explosions between the first and second big explosions was actually ammonium nitrate decomposing, which would imply that this was a pure ammonium nitrate explosion and not one accelerated by some sort of oil or other fuel. If that's true, various manufacturers give the AN to TNT equivalent of poorly handled AN at 15-40% of TNT, giving a yield somewhere in the 412-1,100 tonne range.
However, we know that the explosion wasn't stoichiometrically perfect, because of the brown NO2 clouds that were hanging over Beirut. Properly mixed ANFO should release only H2O, CO2, and N2. So we know that there was some level of explosive power that wasn't fully consumed. This is why I put the ANFO yield as the absolute theoretical max, I think in reality the actual yield was much much lower.
Some other people have speculated that the fireworks like mini explosions between the first and second big explosions was actually ammonium nitrate decomposing, which would imply that this was a pure ammonium nitrate explosion and not one accelerated by some sort of oil or other fuel. If that's true, various manufacturers give the AN to TNT equivalent of poorly handled AN at 15-40% of TNT, giving a yield somewhere in the 412-1,100 tonne range.