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TECHNICAL SPECIFICATIONS <br />USING NSS 37E EPDXY/FRP TANK LININGS <br />PAGE 3 <br />2. PURGING THE TANK OF FLAMMABLE VAPORS <br />A. The tank is to be isolated from any flammable vapor source <br />before work begins. Tanks that are manifolded together <br />create a prevalent danger in that explosive vapors can <br />infiltrate a tank after it has been purged. Submersible <br />pumps must be removed and openings plugged. Lines that may <br />be common to other storage tanks, such as suction, syphon <br />and vent lines, are to be blanked. The CONTRACTOR must be made <br />aware that it is common practice to manifold vent lines at <br />locations where the tanks have been adapted for vapor <br />recovery. <br />B. The tank shall be purged of flammable vapors by use of an <br />air mover constructed of light gage metal of the venturi <br />(jet) type, or low pressure blower. Air movers located in <br />the possible path of vapor travel shall be driven by steam, <br />air or explosion proof electric motors. The apparatus used <br />to inject the air is to be bonded to the tank. <br />C. Purging is to continue as long as the test show vapors in <br />the flammable range are contained in the tank. <br />D. Tests for flammable vapors are to be made with a <br />Combustible Gas Indicator, immediately before cutting or <br />drilling and frequently during the course of the work. <br />Vapor samples are to be taken in the excavation and at the <br />top, middle and bottom of the tank at each testing. It is <br />essential that the operator using the indicator be well <br />schooled in its use and that he perform the checks recom- <br />mended by the manufacturer to insure the instrument is in <br />proper working order prior to the start of each shift. <br />E. Hot work, such as drilling or cutting, shall not be <br />performed when flammable vapors are indicated in the <br />excavation or in the tank. Combustable Gas Indicator <br />readings above 20 Lower Explosion Limit (LEL) are to be <br />considered explosive. <br />2. OPENING THE TANK <br />After it is determine that a safe atmosphere has been <br />established, the tank may be opened. If cutting and drilling <br />are necessary, the tools are to be air operated or run by <br />explosion proof electric motors and bonded to the tank. <br />