The M-HS Single Key Handle Interlock operates on the principle that when the key is "trapped" the handle can be turned and removed opening the interlock. When the handle is re-inserted into the interlock the "trapped" key can then be removed. Once the released key is returned to the Isolator Switch or Key Exchange System power can then be re-applied to the guarded area. Only when the key is removed from the Isolator Switch or Key Exchange System and turned in the M-HS Handle Interlock can the handle be removed and the guard opened. In a die cast mirror polished housing the M-HS Handle Interlock is suitable for SIP and CIP cleaning processes with high pressure hosing with detergents at high temperatures.