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7.6.1.5. Verify that, if tanks are connected by a common venting or vapor-recovery system, that the tank being vapor freed is isolated from the other tanks. 7.6.2. Securely attach a venturi eductor to a tank fitting. The venturi must be rated for a minimum air flow of 1,500 CFM, have no moving parts, and be operated with compressed air. r 7.6.2.1. Where the potential exists for stratification of vapors inside a tank or where very heavy vapors are present, two or more eductors and air blowers may be used in concert in order to improve ventilation. This is accomplished by forcing air into the tank with air blowers at the same time that vapors are drawn out of the tank when using a venturi. NOTE: A venturi eductor should be used for vapor freeing a tank. This system pulls vapors out of a tank, creating a slight negative pressure inside the tank that draws in fresh air. In the event that a diffused air blower is used instead of, or in addition to, a venturi to blow air inside a tank, it must be rated as explosion-proof and meet Zone 1 or Class I, Group D and Class II Groups E, F and G electrical classification requirements. Electrically powered equipment must be inspected before each use to ensure good condition and electrical integrity. 7.6.2.2. Attach an extension to the venturi so that the vapors will be exhausted a minimum of 12 feet aboveground. ® WARM NG Hydrocarbon vapors are heavier than air and can travel along the ground for considerable distances to a remote ignition source. Stop ventilating tanks if atmospheric conditions or the direction of the wind could cause flammable vapors to drift into areas such as adjacent buildings where they might produce a hazardous condition. Failure to do so could result in death or serious injury. 7.6.2.3. Place a drop tube within 12 inches of the tank bottom. If possible, exhaust air from a fill pipe where the drop tube is located. 7.6.2.4. Ground the venturi by connecting it to a grounded metal conduit or placing a ground rod into the earth (according to the manufacturer's instructions) to reduce the possibility of static sparks. 7.6.2.5. Vent the air from the tank for a minimum of 30 minutes before tank entry and keep it running until all repair work has been completed and authorized tank entrants have safely evacuated the tank. 7.6.2.6. Make sure that the forced air ventilation (air forced into the tank from the action of the venturi) comes from a clean, uncontaminated outside source which does not increase the hazards inside the tank. 23