Transform "Staff may open the hatch only when the room is empty" into the formal warning shown. Replace [Staff may open the hatch] to complete: "Under no circumstances ___ while the room is occupied."
Bonne réponse
may staff open the hatch
Explication
The fronted restriction makes the fixed modal precede the subject, followed by the bare verb and its object. Subject-before-modal order would fail to form the required negative inversion.