3. Clean out pipelines. 4. Remove contaminated tanks from service and clean them thoroughly. 5. Recirculate fuel and return it to the system up- stream of as many falter/separators as possible. 6. Investigate the source of contamination and eliminate it. Notify cognizant Military Inspection Serv- ice and Navy Fuel Supply Office if fuel is contaminated on receipt. Commingling The inadvertent mixing of two or more different fuels  is  known  as  commingling.  Most  hydrocarbon products (greases, oils, alcohols, and so on.) are readily capable of mixing with other hydrocarbon products and cannot be separated by mechanical means such as set- tling, filtering, or centrifuging. A fuel that has been contaminated by commingling with another petroleum product is extremely dangerous whether in storage or in use, because there may be no apparent visual or odor change. This type of contamination is usually caused by carelessness or a misunderstanding of the operations of a fuel system. Most fuels systems are segregated from each other and from other types of fuel systems; but in some cases the piping of one fuel system may be inter- connected with another system through valves, blanks, or flanges. The inadvertent opening of a wrong valve can result in commingling the two different products. In other instances, fuel maybe pumped into a tank that has contained another product without the tank being properly cleaned. The small amount of the other product may be enough to contaminate the fuel. JP-5 contaminated with other jet fuels or gasoline must not be stored aboard aircraft carriers unless a laboratory test indicates that the flash point is within the allowable limits of the specifications. Because of the problem in detecting commingled fuels, you must be careful where two different fuels are handled in close association. INSPECTION OF FUEL The fuel systems and mobile refuelers now in use by  the  Navy  are  designed  to  deliver  an  acceptable uncontaminated fuel safely into the tanks of an aircraft when they are properly operated. To ensure that this fueling equipment is working properly and is being operated properly, samples of the fuel must be taken at several points and after each step in the operation. SAMPLES A sample is a small part of a quantity of a fuel representative of the quality or condition of the total quantity of that fuel, suitable for visual or chemical examination. All ABFs must know the procedures for drawing of samples and examining them for visual contamination. A sample must be taken in such a manner and from such a location that the sample will be a true representative of the fuel sampled. Many types of samples and sampling methods are used in the inspection of fuels. The four most common ones are discussed here. Composite Sample A  single  tank  composite  sample  is  a  blend  of samples taken from the upper, middle, and lower lev- els of a tank’s contents. A multiple tank composite sample is a blend of individual all-levels samples from each of the tanks that contain the same type of product being sampled. These samples are in proportion to the volume of the product in each tank. All-Levels Sample This  sample  is  one  obtained  by  submerging  a closed sampler (thief’) to a point as near as possible to the drawoff level, then opening the sampler and rais- ing it at such a rate that it is nearly but not quite full as it emerges from the liquid. Line Sample A line sample is one taken from a pipeline or hose at  or  near  the  discharge  point  before  commencing delivery and during the first few minutes of pumping. This sample is taken to give an initial visual identifi- cation of the fuel. Representative  Sample This type of sample is used for packaged stocks of fuel. One container from a large stock of packaged fuel when all are of the same age and grade may be selected as a representative of the entire stock. When the con- tainers of fuel are small and suitable for shipment, a container of fuel is taken as the sample without its being opened. For drums of fuel, the sample is drawn from one drum. 3-11