I found an article describing the mechanism of action of these massive "fuel-air" bombs: (Wikipedia)  "A thermobaric weapon is a type of explosive that utilizes oxygen from the surrounding air to generate an intense, high-temperature explosion. .... They are considerably more destructive when used against field fortifications such as foxholes, tunnels, bunkers, and caves—partly due to the sustained blast wave, and partly by consuming the available oxygen inside."  Please note that they "consume the available oxygen inside" - which makes the weapon's actions similar to poison gas that suffocates the victims.