[mathiasrw]

When the constriction of the twin towers started in 1968 asbestos was used for insulation.

In April 1970, the New York City Department of Air Resources established asbestos spray insulation regulations. As a result, the Department ordered contractors to stop the use of asbestos in the World Trade Center. The upper levels of the north tower and the entirety of the south tower contained asbestos alternatives.

It's estimated that the north tower contained 300 – 400 tons of asbestos.

[ncmncm]

I am corrected.