Document Eva98Zv9YLK27yqQdEV50dq6L

cleaning procedures and other precautions Small tanks and drums should be cleaned and steamed in an open-faced building with ample roof ventilation It is even preferable to clean them in an outside area free from ignition sources Pipes and nozzles should be electrically bonded to containers being steamed Covers, plugs, and valves should first be removed and the tank or drum permitted to drain into a container The inside should be examined for rags, waste, or other debris that might interfere with draining and retain flammable vapors Only lights approved for use in the National Electrical Code Class I, Division I, Group D hazardous locations should be used for this inspection, see expla nation m the previous chapter Mirrors can sometimes be used to reflect daylight inside for this purpose Steaming. Steaming, hot chemical wash, water filling, and use of inert gas are among the common methods for cleaning and vaporfreeing small tanks and drums If the inside of the container is clean and steam is avail able, the easiest method is to steam it (See American Welding Society, Safe Practices for Welding and Cutting Containers That Have Held Combustibles Also see NFPA Stand ard 327, Cleaning or Safeguarding Small Tanks and Containers) The tank or drum, placed on a steam rack or over a steam connection with the outlet holes at the lowest point, should be allowed to drain The tank or drum should rest against a steam pipe or should be bonded An ample supply of live steam should then be applied for a period of not less than ten minutes The inside of the drum should be washed with hot water and, after being cooled, tested with a combustible gas indicator If the drum tests vapor free, hot work repairs can then proceed If not, it should be cleaned and steamed further It is sometimes advisable to mark the drum to signify that it is vapor free If steaming will not clean the tank or drum, a cleansing compound of sodium silicate or tnsodium phosphate (washing powder) dis solved in hot water and kept at a tempera ture of 170 to 190 F should be used Hot water should be added to overflow the con tainer until no appreciable amount of volatile liquid, scum, or sludge appears Exceedingly dirty containers may require a caustic soda solution (except aluminum and zinc coated drums in which caustic soda may generate hydrogen), agitated enough to ensure that interior surfaces are thoroughly cleaned They can then be drained, washed, and steamed If steam is not available to heat the water, a cold water solution with an increased amount of cleansing compound can be used The solution should be agitated to ensure cleaning To guard against burns, especially when they are using steam, hot water, and caustic soda, workmen should be protected with suitable clothing, such as boots, gloves, face shields, and rubber aprons Because of its low ignition temperature, drums that have contained carbon disulfide should not be steamed They should be made vapor free with a cleansing compound, and then gas tested Small tanks can be made safe by means of an inert gas, but this method is not gen erally considered as safe as steaming Portable inert gas generators are available for special jobs, but they should be used only by well qualified men who can produce proper atmosphere and safeguard against fire or explosion Carbon dioxide and nitrogen are some times used to make small tanks and drums that have contained flammable liquids safe for hot work repairs When an inert gas like carbon dioxide or nitrogen is used, the tank or vessel is washed as free as possible of flammable liquids and flushed thoroughly, so that the vessel over flows As much water as the repair work will permit should be left in the tank, and carbon dioxide should be introduced to produce a concentration of not less than 50 per cent by volume, except that if the tank has contained hydrogen or carbon monoxide, 80 per cent concentration is required Nitrogen concentrations should be 60 per cent or higher, depending on the previous contents of the container Abandonment of tanks Tanks to be permanently abandoned should be thoroughly washed out and made safe 1039