After an attack on the villa in June, fortification was increased. According to CNN, fortifications "included additional barriers and barbed wire, increased lighting, chain link fences, additional sand bags and closed circuit television. Every U.S. building on the compound was also fitted with a safe room with a steel door, although the officials recognize that the room was not fireproof."
There is no such thing as a safe room that's not fireproofed.
But not only was not one single room fireproofed, the place had no fire extinguishers and no smoke masks for the employees.
That last was reported by the Wall Street Journal.
As to whether the attackers knew the employees were completely unprepared to deal with an arson attack, they showed up with diesel fuel cannisters that they lobbed into the villa. Burning diesel fuel makes very thick black smoke.
CNN, September 24, 2012: U.S. post in Benghazi had less than standard security before attack
The Wall Street Journal, September 27, 2012: The Libya Debacle: The more we learn, the more Benghazi looks like a gross security failure.