After loading a fresh cup of Lead Azide (ca. 1kg explosive mass), the operator returned to the loading cubicle after an “unlatched chimney door” signal interlock prevented normal operation. An initiation occurred whilst the operator was in the cubicle and close to the chimney. The loading chimney contained the explosion and any projectile action and the operator was unhurt. He was exposed to high blast noise however, and after medical observation was returned to duties.