Turkish authorities detained seven people over Wednesday's explosion at the Tupras refinery, in the city of Izmir.
The explosion, which killed 4 people, was a result of gas entrapment.
Following the explosion, the Minister of Labor and Social Security Julide Sarieroglu instructed the launch of an investigation in which three chief inspectors and one inspector were assigned to lead enquiries.
Within the scope of the investigation, Tupras operation's Chief Engineer Kursat K, Chief Engineer Mehmet Emin T, Operations Engineer Burak K, Operations Safety Specialist Esfet B., the subcontracting firm Beka Project's official Bedrettin K, Site Manager Muhammed Hulusi G and Chief Assembly worker Ali B. were taken into custody.
Meanwhile, the gathering of evidence related to the explosion continues.
Reporting By Mustafa Yildirim
Writing By Murat Temizer