Safety precautions must be taken before any heater, boiler, flue duct, or stack is entered. In general, these precautions include but may not be limited to isolating energy sources, lock-out-tag-out, atmospheric gas checks and reduction of confined space temperatures before entering. Dust and acid-containing material on internal surfaces are to be expected. The problem they present may be complicated if fuel-oil additives that leave toxic residues have been used. Protective equipment must be made available and used until it has been determined that safe conditions exist. When vanadium dust is present, protective apparatus and clothing must be used when internal inspections are performed. Consult all applicable common site-specific, OSHA and other federal, local, and state safety rules and regulations.