Non-OEM recommended safety pin was used and fell, causing the lock pin slipped out of the pin holes which was installed wrongly i.e. upside down. Later attempt to re-install lock pin failed as the pin holes were not aligned When a new hazard have been identified during operation the MWD Engineer Supervisor, Directional Driller and Rig Driller failed to conduct dynamic risk assessment before making the decision to continue with the operation MWD Kit#14 was not inspected on rig site to confirm inventory availability as per checklist enclosed to identify missing OEM safety pin Original Equipment Manufacturer (OEM) lock pin was not ‘failed proof’ design i.e. it can be inserted into the pin holes from top and bottom. The risk of MWD string falling off the lifting clamp was recognized therefore non-essential personnel were cleared off the rig floor.