69 when any drawer 3 is opened since there is no drawer associated with the upper end of the catch 15a no u shaped tab is required at the upper end of that catch it is also impossible to open any drawer 3 beneath an opened drawer opening a drawer such as drawer 3c does not displace any of the catches such as catch 15d located below the opened drawer consequently the gaps g remain aligned with the associated retainers 17 on the lower drawers fig4 and 6 the retainer nose 67 of a lower drawer that is attempted to be opened will enter the associated gap the retainer tapered surface 47 will strike the tab center leg 33 of the catch immediately above that retainer and try to displace that catch upwardly upward catch displacement is not possible however because vertical displacement of the catch is blocked by the retainer of the opened drawer particularly in fig2 b and 7 drawer 3d cannot be opened because the top tab leg 35d will strike the undersurface 53c of the catch 17c upward displacement of catch 15d is thereby blocked as a result the safety interlock 13 of the present invention permits only one cabinet drawer to be opened at a time as illustrated in fig1 and 2b the design of the filing cabinet 1 may be such that the back walls 51 of the drawers 3 are forward of the column of catches 15 when the drawers are in the fully opened position to maintain the expanded gap eg when a retainer 17 has moved forward of the catches the retainer slide 19 reciprocates within the retainer to remain.