 There are many types of loud sharp noises that are not caused by explosives, and seismographic records of the collapse do not show evidence of explosions.Jones and others have argued that horizontal puffs of smoke seen during the collapse of the towers would indicate that the towers had been brought down by controlled explosions.NIST attributes these puffs to air pressure, created by the decreasing volume of the falling building above, traveling down elevator shafts and exiting from the open elevator shaft doors on lower levels.