High security manhole insert cover

A high security manhole insert requiring no adaptation to an existing manhole, a manhole entrance or a manhole cover, the manhole insert placed within the manhole entrance to provide a high security blockade to ingress or egress to the manhole from above and below, the high security manhole insert comprising essentially:

• a circular perimeter rim having an upper flange upon which the manhole cover is replaced after installation of the manhole insert to the manhole entrance;
• a lower plate connected to the perimeter rim;
• an upper plate having a recessed cylindrical access hole including a cylindrical lock housing, said upper plate attached to the perimeter rim above the lower plate, with the perimeter rim, the upper plate and the lower plate further defining an inner cavity, within which is placed;
• a rotatable locking means having;
• a central slot, activated by a slot key,
• a plurality of extendable locking arms extending through the perimeter rim, said extendable locking arms extended by the rotation of the rotatable locking means,
• wherein the lower plate prevents access to the rotatable locking means from below while the upper plate limits access to the rotatable locking means through the recessed cylindrical access hole in said upper plate, said cylindrical lock housing adapted to accept a cylindrical lock having a vertical locking member, said cylindrical lock including an upper surface which should lie flush with an upper surface of the upper plate when said cylindrical lock is locked by a key within said cylindrical lock housing, the entire manhole insert comprised of a high strength metallic composition.