Abstract: A safety knife comprises a knife body (10), a blade carrier (16) movable within the knife body (10) between a retracted position and an extended position, biasing means (24) urging the blade carrier (16) towards its retracted position, latch means to latch the blade carrier (16) in its extended position, and a weight (36) movable along a passage (32) relative to the knife body (10) and engageable with release means (40) to release the latch means.

Abstract: A safety knife comprises a knife body (10), a blade carrier (16) movable within the knife body (10) between a retracted position and an extended position, biasing means (24) urging the blade carrier (16) towards its retracted position, latch means to latch the blade carrier (16) in its extended position, and a weight (36) movable along a passage (32) relative to the knife body (10) and engageable with release means (40) to release the latch means.

Abstract: A safety knife comprises a handle and a blade mounted on the handle so that a part of the blade projects from the handle. Two retractable safety guards are also mounted on the handle, overlying opposite sides of the projecting portion of the blade. Each guard is spring-loaded so that pressure from the material being cut causes the guards to retract into the handle as the blade cuts into the material. A manually controlled locking device normally prevents the guards being retracted but, when operated, allows the guards to retract. The guards automatically extend, under the action of springs, when the knife is removed from the material.