Stop the presses! Or at least make sure to lockout and tag before you do any maintenance on your rotary airlock valve.
On that note, ACS Valves recently published an extensive guide to rotary valve safety in Powder & Bulk Solids. It describes the role of valves in NFPA safety and outlines the key safety considerations you should have in mind any time you work with rotary valves. Give it a read online or look for it in print.
Stay safe out there!