Improper changing over of duplex filter causing oil splash and injury

Summary:
Duplex filter shows clogged so 4E changed over filter and tried to open vent valve but vent valve not getting opened. So 4E slackened the cover nut and suddenly oil got splashed all around, corrected the change over of filter properly, then oil stopped leaking

Corrective Action/ Lessons to be learnt:
Check the indication of change over for correct position, before attempting any work to open it

Incident:
Vent valve is welded, so not opening ; without observing proper change over , it was tried to open, leading to oil splash and injury
Changeover is not completely done