GENERAL Preparatory work usually involves conventional storage tanks@ spheres@ process vessels@ and other equipment which may have to be entered. However@ in principle@ it also applies to furnace fireboxes@ ducts and flues@ large sewers@ electrical vaults@ deep sumps@ pits and excavations@ or any enclosed or confined location from which ready escape of workers may be difficult or in which toxic or flammable materials may be present. Some of the factors that usually should be considered are: 1. Condition of the atmosphere for safe breathing. 2. Prevention of fires or explosions. 3. Provision for ready entry and exit. 4. Avoidance of contact with toxic or corrosive substances or hot steam@ which be harmful to personnel. 5. Assurance of safe footing and prevention of hazards from falling materials. 6. Assurance of safe working temperatures. 7. Electrical@ radiological@ oxygen content@ or other special fire and safety problems.