The NIST discovered that in 1999 the Port Authority issued guidelines to upgrade the fireproofing to a thickness of 1 1 / 2 inches .
In 1999 , NIST found , the Port Authority issued guidelines to upgrade the fireproofing to a thickness of 1 1 / 2 inches .
In 1999 , the building 's owners , the Port Authority of New York and New Jersey , issued guidelines to upgrade the fireproofing to a thickness of 1 { inches .