ASTM D6986 Standard Test Method for Free Water, Particulate and Other Contamination in Aviation Fuels (Visual Inspection Procedures)
8. Procedures
8.1 Procedure A - Clear, Transparent Containers:
8.1.1 Open Glass or Plastic Container:
8.1.1.1 Visual Observation - Fill container about three-fourths full. Immediately check for evidence of water or particulate contamination by holding the sample to the light and visually examining for haze or lack of clarity. Close the container and swirl the sample to produce a vortex and examine the bottom of the vortex for particulate matter and water droplets. Also look for brown slime or a water layer on the bottom of the container. Record the particulate and water appearance rating of the sample using the ratings in Tables 1 and 2. Record the appearance of any other contaminant using Table 3 as a guide. Record the ambient temperature.

8.1.1.2 Use of Bar Chart and Photographs - Immediately on drawing a sample, place the container into a well-lighted area, avoiding light reflections on the front of the container as much as possible. Place the bar chart directly behind the container, with the lines toward the container and parallel with the bottom of the container. The narrowest line should be at the bottom of the container. Directly facing the container and bar chart, compare the appearance of the bar chart through the sample with the standard photographs. Place the photographs next to the container so that they are lighted similarly to the sample. Select the photograph closest in appearance to the sample. Notice that the differences between photographs consist both of the successive disappearance of lines as well as the gradual lightening of all the lines. Record the number of the thinnest line which is visible through the sample, or record "six" if no lines are visible.

8.1.2 Closed Circuit Sampler:
8.1.2.1 With fuel flowing under pressure in the main fuel line, open the fill valve wide, filling the glass jar to within about 25 mm (1 in.) from the top.

8.1.2.2 Let the product settle for 1 min or more, if necessary, to remove air bubbles. (Caution - The visual results may differ from the photographs if the circuit sampler has a diameter different from that of the 100 mm (4 in.) jar used in the photographs.)

8.1.2.3 Examine the glass sampler for hazy/cloudy conditions and the bottom for water droplets, solid contaminants, brown slimes, or a combination thereof. Record the particulate and water appearance ratings of the sample using the ratings in Tables 1 and 2. Record the appearance of any other contaminant using Table 3 as a guide. If desired, the bar chart and photos can be used to rate sample clarity as described in 8.1.1.2. Record the ambient temperature.

NOTE 3 - While small water droplets and air bubbles may appear similar, air bubbles will rise while water droplets will settle upon standing.

8.1.2.4 If the sampler is fitted with an optional self-sealing valve assembly for a free water field testing kit, a fuel sample may be drawn at this time.

8.1.2.5 Open the drain valve to drain the sampler.

8.2 Procedure B - Opaque Containers:
8.2.1 White Bucket - In the U.S., only the white porcelain bucket is recommended for the optimum detection of red dye contamination.
8.2.1.1 Bond the bucket electrically to the fuel system or to the ground by using a bonding wire.

NOTE 4 - When using a white porcelain bucket, the porcelain coating should not be thought of as an insulating layer for electrical bonding.

8.2.1.2 If necessary, wipe external contamination from the fill valve. Flush the sampling tap of loose contaminants at maximum flow rate prior to drawing the sample.

NOTE 5 - Water lying on a flat surface forms a meniscus around the drain port. With low velocity, clean fuel goes through the port, leaving the water and other contaminants in place. Velocity breaks the meniscus, so that much of the surface accumulation can be entrained.

8.2.1.3 Open the fill valve as wide as possible to avoid the collection of contaminants behind a partially closed valve. Fill the bucket to a depth of about 150 mm (6 in.).

8.2.1.4 Allow the sample to stand for 1 min or more, if necessary, to remove air bubbles.

8.2.1.5 To concentrate any solids or water droplets, or both, in the center of the bottom, the contents can be swirled carefully by using a clean implement.

8.2.1.6 Inspect the bottom of the bucket for evidence of solids.
(1) Using Table 1, assign a letter rating which matches the appearance of the solids on the bottom of the bucket.
(2) If desired, the particle photographs of the Particle Assessment Rating Guide can be used to assist in the assignment of the letter rating.

8.2.1.7 Inspect for haze or water droplets. Haze can also be detected by dropping a shiny coin into the bucket. If the characteristics of the coin can easily be distinguished, the product is considered clear. Using Table 2, assign a rating for water contamination appearance.

8.2.1.8 Inspect for fuel color and other unusual appearance such as brown slime or scum. Record the ambient temperature.

NOTE 6 - Unusual color in aviation fuel may indicate mixing with another product. Both clear and opaque containers can be used to observe product color. However, informal tests have shown the clean white porcelain bucket to be most suited to the detection of unusual color such as contamination with low concentrations of dyed fuel or color resulting from crude oil characteristics or refinery processing.

NOTE 7 - At the time of this writing (2002), in the U.S., the required dye color for certain diesel fuels or heating oils is red.

NOTE 8 - Sample clarity is best checked by viewing the sample illuminated with transmitted light through a clear container.
(1) Using a clean porcelain-coated bucket filled to a depth of about 150 mm (6 in.), look for visual evidence of unusual color, viewing the sample under normal daylight conditions or under daylight balanced light.
(2) The operator shall have normal, color vision and shall not wear tinted glasses.
(3) If there is doubt about whether unusual coloration is present, a consensus on the color should be obtained from several individuals.

8.2.1.9 Record the appearance of the sample, using one of the particulate and one of the water content ratings in Tables 1 and 2, respectively. Record any other observed contamination using Table 3 as a guide.