Take proper precautions when working around dangerous substances by complying with the 2010 NFPA 326.
NFPA 326: Standard for Safeguarding of Tanks and Containers for Entry, Cleaning, or Repair outlines the basic procedures to safeguard a tank or container that contains or has contained a flammable, combustible, or otherwise hazardous substance before entry, cleaning, repair, or other activities can be performed. This Standard incorporates relevant parts of NFPA 327: Standard Procedures for Cleaning or Safeguarding Small Tanks and Containers Without Entry.
The 2010 edition has been revised by updating of all referenced publications. (Softbound, 19 pp., 2010)