Yousef was assisted by Iraqi bomb maker Abdul Rahman Yasin [1] . Yasin's complex 1310 lb (600 kg) bomb was made of urea pellets, nitroglycerin, sulfuric acid, aluminum azide, magnesium azide, and bottled hydrogen. He added sodium cyanide to the mix as the vapors could go through the ventilation shafts and elevators of the towers.
The Ryder van used in the bombing had 295 ft³ (8.3 m³) of space, which would hold up to a ton (907 kg) of explosives. However, the van was not filled to capacity. Yousef used four 20 ft (6 m) long fuses, all covered in surgical tubing. Yasin calculated that the fuse would trigger the bomb in twelve minutes after he had used a cigarette lighter to light the fuse.
Yousef wanted the smoke to remain in the tower, therefore catching the public eye by smothering people inside, killing them slowly. He anticipated Tower One collapsing onto Tower Two after the blast. The materials to build the bomb cost approximately US$129
The bomb exploded in the underground garage at 12:18 P.M., generating a pressure estimated over one GPa and opening a 30-meter-wide hole through four sublevels of concrete. The detonation velocity of this bomb was about 15,000 ft/s (4.5 km/s). The cyanide gas generated is assumed to have burned in the explosion.
Six people were killed. At least 1,040 others were injured. However, the towers were not destroyed as Yousef intended. However, the WTC’s architect would later tell jurors that if the van had been left closer to the poured concrete foundations, they would have succeeded. The tower would have fallen.[2] Yousef escaped to Pakistan several hours later.
The bomb cut off the center's main electrical power line and cut off telephone service for much of lower Manhattan. The bomb caused smoke to rise up to the 93rd floor of both towers, and cut off the towers' four stairwells and emergency lighting system. Also as a result of the loss of electricity most of New York City's radio and television stations lost their over-the-air broadcast signal for almost a week, with television stations only being able to broadcast via cable and satellite via a microwave hookup between the stations and three of the New York area's largest cable companies, Cablevision, Comcast, and Time Warner Cable.