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and that authorized tank entrants and crew members are qualified to perform this work <br /> based on the requirements spelled out in the procedure. <br /> 7.4.2.2. Do not issue a permit if oxygen, flammable-vapor and toxic-substance levels are <br /> not within acceptable levels as defined in Table 2. <br /> 7.4.2.3. Review the completed permit with each crew member before tank entry. Sign and <br /> date it where indicated and post it at the tank-entry location. <br /> 7.4.2.4. Order corrective measures as necessary to ensure conditions at the jobsite and <br /> inside the tank are safe. <br /> 7.4.2.5. Cancel the permit if conditions develop that may put authorized tank entrants at <br /> risk of injury. <br /> 7.4.2.6. Cancel the permit when the work is completed. Permits should only extend for the <br /> duration of the task. A permit must be canceled at the end of each day and a new permit <br /> must always be issued at the start of a new day. <br /> 7.5. Control of Ignition Hazards <br /> 7.5.1. Before any work is done that might involve the release of flammable vapors, <br /> eliminate all sources of ignition such as smoking, welding and grinding where flammable <br /> vapors may be present or may travel. Note; Electric heat guns are a potential ignition <br /> source and, therefore, are not allowed at the jobsite. <br /> 7.5.2. Use only approved lighting inside a tank. Refer to Appendix D, "Control of Ignition <br /> Sources," for detailed information on this subject. <br /> 7.6. Venting the Tank <br /> 7.6.1. General <br /> 7.6.1.1. Conduct vapor and gas freeing (venting) to remove flammable or toxic vapors from <br /> a tank by displacement or by reducing the percentage of vapors and gases in the tank's <br /> atmosphere to a safe level by dilution with fresh air. <br /> 7.6.1.2. Restrict all maintenance work in the immediate area surrounding the tank during <br /> the initial stages of vapor freeing and while the tank may contain high concentrations of <br /> flammable vapor. <br /> 7.6.1.3. Prohibit all potential sources of ignition during vapor freeing. <br /> 7.6.1.4 Verify that there is another tank opening(s) sufficient in size so that introducing <br /> induced air into the tank with a venturi does not prohibit the tank from maintaining its <br /> atmospheric pressure. <br /> 22 <br />