From the first floor window and debris spread, it is concluded that the first floor had an explosion occur, and the extensive damage to the outer wall of the 2nd and 3rd floor, show that it was very high temperture, so it is likely that an liquid like gasoline or other was used to start and make the fire bigger"
Normal fire inside a building don't reach temperature over 1000 degree, but gasoline fire can reach over 1500 degree, able to melt metal at that temperture it is impossible to breath, people on the first floor was perished quickly, 2nd and 3rd floor heard the explosion, but before had time to reach, the fire and smoke came, and they didn't had time to run/react.
Due to the unatural speed and spread of the fire, likely rising a few meter after igniting so spreading very fast, there wasn't time for the fire alarm and fire door to activate, making escape impossible, the only secure way now is to increase checking of personal item and coming in and out of building.