On 4/17 QC samples were being collected from a conveyor belt. Lockout requirements were not followed. The belt was accidentally activated by another employee for a few seconds. IP's knee contacted a conveyor x-member. No reportable injury was communicated. On 4/28, IP reported that while walking at a lake his knee gave out on 4/26. IP came to work on 4/28 on crutches & light duty.