Fire Safety Integral Tanks 14-49 Figure 14-91.  Wear a nonstatic protective suit and respirator when entering an integral fuel tank for inspection or repair.  Breathing air supply input Cotton cap (without visor) Respirator Approved coverall Safety line Air supply hose Cotton socks Standby respirator Once the location of the leak is determined, the tank sealant  is removed, and new sealant is applied. Remove old sealant  with a nonmetallic scraper. Aluminum wool can be used  to remove the final traces of the sealant. After cleaning the  area with the recommended solvent, apply new sealant as  instructed by the manufacturer. Observe cure time and leak  checks as recommended before refilling the tank. A fire extinguisher should be on hand during fuel system  maintenance or whenever fuel is being handled. A fuel  AVGAS is especially volatile. It vaporizes quickly due to its  high vapor pressure and can be ignited very easily. Turbine  engine fuel is less volatile but still possesses enormous  capacity to ignite. This is especially true if atomized, such as  when escaping out of a pressurized fuel hose or in a hot engine  compartment on a warm day. Treat all fuels as potential fire  hazards in all situations. As was discussed, empty fuel tanks  have an extreme potential for ignition or explosion. Although  the liquid fuel has been removed, ignitable fuel vapor can  remain for a long period of time. Purging the vapor out of  any empty fuel tank is an absolute necessity before any  repair is initiated. An observer is stationed outside of the tank to assist the  technician in the tank.  [Figure 14-91]  A continuous flow of  ventilating air is made to flow through the tank. A checklist for  fuel tank preparation for entry taken from a transport category  maintenance manual is shown in  Figure 14-92.  The details of  the procedures are also given in the manual. Other integral fuel tank leaks can be more challenging and  time consuming to repair. They occur when the sealant used  to seal the tank seams loses its integrity. To repair, fuel needs  to be transferred or defueled out of the tank. You must enter  large tanks on transport category aircraft. Preparing the tank  for safe entry requires a series of steps outlined by the aircraft  manufacturer. These include drying the tank and venting it of  dangerous vapors. The tank is then tested with a combustible- gas indicator to be certain it can be entered safely. Clothing  that does not cause static electricity and a respirator is worn.  Fuel vapor, air, and a source of ignition are the requirements  for a fuel fire. Whenever working with fuel or a fuel system  component, the technician must be vigilant to prevent these  elements from coming together to cause a fire or explosion.  A source of ignition is often the most controllable. In addition  to removing all sources of ignition from the work area, care  must be exercised to guard against static electricity. Static  electricity can easily ignite fuel vapor, and its potential for  igniting fuel vapor may not be as obvious as a flame or an  operating electrical device. The action of fuel flowing through  a fuel line can cause a static buildup as can many other  situations in which one object moves past another. Always  assess the work area and take steps to remove any potential  static electricity ignition sources. Occasionally, an integral tank develops a leak at an access  panel. This can often be repaired by transferring fuel to another  tank so the panel can be removed and the seal replaced. Use  of the proper sealing compound and bolt torque are required. 