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The World Trade Center Bombing

Reprinted from Law Enforcement Technology

Sifting Through the Rubble

When a bomb exploded at the World Trade Center rescue personnel, bomb technicians and special investigators all worked round the clock with technology there to lend a helping hand.

The blast at New York's Twin Towers that resulted in six dead, over 1,000 injured, and millions of dollars in property damage, left bomb technicians and special investigators working round the clock, seven days a week, sifting through hundreds of tons of debris.

Specialists with the New York City Police Bomb Squad, the FBI, and Bureau of Alcohol, Tobacco, and Firearms, carefully and painstakingly looked for metal fragments, wires, and especially for the bomb fusing device that led to the fatal explosion. For every dump truck load of debris hauled from the bomb site, about one bucketful of twisted metal fragments, wires, vehicle components, and other suspicious items, were tagged and set aside for further study.

To help speed the search for evidence, investigators placed shovelfuls of rubble onto the top screen of a Kason VIBROSCREEN Circular Screen Separator at one of three debris sifting sites. Kason Corporation of Millburn New Jersey, manufacturer of separators, centrifugal sifters and sieves, had sold the VIBROSCREEN separator to the FBI in 1988 for investigative work. Since the unit weighs less than 200 pounds, it can be easily transported by truck or van to different sites.

A 24 in. diameter unit with a gyratory motor that vibrates at 1,200 revolutions per minute, the VIBROSCREEN has three screens which allow debris to be classified and separated by size. Materials larger than the one inch screen openings of the top screen, such as pieces of concrete, remain on the top. More finely sized material dropped through the top screen to a second two mesh screen with 0.437 in. openings where horizontal and vertical motion by the 1/3 hp, 115 volt gyrator caused oversize material to exit through a discharge spout and finer material to drop through the mesh onto a third 6 mesh screen with 0.1318" openings. Material passing through that screen dropped onto a ramp leading to a fourth discharge spout with connectors taking classified debris to pails. The finest debris, measuring less than 1/8 inch, was disposed of without inspection.

Pails of classified debris were then dumped onto square screens of various mesh sizes and examined by investigators under powerful lights. Only after methodically viewing all debris on the screens by leveling it to single particle bed depth and examining each piece, was the debris disposed of.

Kason also supplied a larger screen for work at the World Trade Center at the time of the investigation.