ANKARA (Reuters) - Turkish authorities arrested four people over Wednesday s explosion in a storage tank at a Tupras refinery which killed four people, the state-run Anadolu news agency said on Saturday. The explosion occurred following maintenance work at the refinery in the western Turkish province of Izmir, wounding two other workers, but had no impact on production. On Thursday, authorities had detained seven people over the blast, of which four have been formally arrested and three have been released on probation. The report gave no details of what charges the four may face. 