I wonder if an EOD expert could explain if that browning color signifies the presence of anything important.
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Not, specifically, an "EOD expert" -- but this physical chemist attributes the brownish-orange-reddish colored smoke to oxides of nitrogen from decomposition (deflagration + detonation) of ammonium nitrate.
("Orange" smoke is a classic signature of an ammonium nitrate explosion.)
In April of 1947 -- from my classroom in Webster, Texas -- I personally witnessed the orange mushroom cloud from the massive explosion of ammonium nitrate aboard the SS Grandcamp in Texas City, Texas. (It reminded me of the orange fumes in the top of bottle of concentrated nitric acid...)
Even then, I told my classmates that it was a chemical (not petroleum) explosion -- but the smoke soon turned black as the adjacent petrochem plants and "tank farms" ignited. The same thing happened in OKC: most [later] photos show black smoke from the burning vehicles in the parking lot across the street from the Murrah Building. (See my FRProfile re OKC...) The same "orange-to-black" smoke color shift occurred in Beirut as the surrounding area began to burn.
BTW, the gray-white smoke in Beirut was from the fire (including fireworks) in the northern warehouse -- before the ammonium nitrate explosion in the southern warehouse.
TXnMA