Federal investigators have embarked on the monthslong probe into the fatal disaster at Nippon Dynawave Packaging (NDP). …The U.S. Chemical Safety and Hazard Investigation Board said it aims to release a final report in 12 to 18 months. An investigative update is expected within three to five months. Four Chemical Safety Board investigators remain in Longview as of Tuesday. …Investigators are focused on four key areas, Wingard said: mechanisms that led to the tank’s failure; the tank’s location at the facility; the paper mill’s maintenance and mechanical integrity; and relevant facility, corporate and industry standards. …The Washington State Department of Labor and Industries launched a workplace safety investigation immediately after the tank ruptured. …The Washington State Department of Ecology is probing whether NDP violated its environmental permits. …The US Chemical Safety Board seeks to identify the root cause of industrial incidents — regardless of whether existing regulations were violated. [to access the full story a Seattle Times subscription is required]