API Publ 2207:1998 pdf download.Preparing Tank Bottoms for Hot Work
This publication outlines safety precautions for preventing accidental Þres and explosions when hot work is performed on tank bottoms. The term hot work, as used in this publica- tion, is deÞned as an operation that can produce a spark or ßame hot enough to ignite ßammable vapors. This publication may not contain all safety precautions and procedures that may be required prior to or during a speciÞc hot work activity. All hot work should be performed in com- pliance with applicable national, state and local regulatory requirements and recognized industry practices, including but not limited to: conÞned space procedures, lockout/tagout pro- cedures, and requirements for personal protective equipment (see OSHA Regulations 29 CFR part 1910 and API Publica- tions 2015 and 2217). Tanks that have contained ßammable or combustible liq- uids, regardless of their age and type of construction, must be considered unsafe for hot work until approved by safety inspections. These inspections include gas testing to determine if the oxygen content of each tank is between 19.5 and 22.5 percent. Special techniques are required in the per- formance of hot work on tank bottoms to prevent the ignition of ßammable vapors that may be trapped under the tank. Although each repair of tank bottoms must receive careful consideration, the safety procedures described in this publi- cation provide various methods for preparing tank bottoms for hot work. These procedures will apply to most situations.
As an alternative to scraping down to bare metal, welders should use air-supplied respiratory equipment. If the area described above is not scraped down to bare metal and as long as frequent air-quality tests during the hot work indicate a safe atmosphere, it may be unnecessary for other personnel in the tank to wear air-supplied respiratory equipment (see API Publication 2015). 3.2.5 Grounding leads from the welding machine should be attached directly to a bared surface on the tank shell on which hot work is to be performed. Welding leads should be carefully inspected for insulation abrasions, cuts, scuffs, or breaks; any of these can cause shorting. 3.2.6 Compressed-gas cylinders used for cutting operations should be securely fastened in an upright position and kept outside the tank at a safe distance from the open manholes. When not in use, cutting torches and hoses must be shut off at the cylinder valves and kept outside the tank. Com- pressed-gas supply hoses and hose connections should be inspected for leaks prior to being taken inside the tank. To prevent a possible ßammable mixture with air from forming in the tank, compressed-gas supply hoses must be protected from damage outside the tank and from burns, cuts, breaks, or other damage inside the tank.