color, appearance, gravity, or odor of the product. However, sometimes contamination can only be detected by a
laboratory and all products suspected of contamination should be reported to the chain of command. Some of the
more common types of contamination are:
(1) Dirt. The presence of dirt in a petroleum product is usually the result of inadequate cleaning and
inspection of tanks or containers.
(2) Rust. Rust is the product of the corrosion of metal. It is brittle, powders readily, and insoluble in
water. It may form troublesome suspensions.
(3) Mill-Scale. This is a magnetic product formed during manufacturing of metal parts. It is largely
responsible for the blue-black appearances on finished metal surfaces. It is a very serious contaminant in bulk
products pumped through new pipes during the first few days or weeks of use. The scale is brittle and cracks
readily. Corrosion starts at these cracks and spreads under it causing it to flake off. Settling is not a satisfactory
method of eliminating the scale, and filtering is recommended.
(4) Water is present in all fuel systems, as it can enter the system at any point. The water may be
present as dissolved (not visible to the naked eye), entrained (gives the product a hazy appearance), or free water
(droplets in the bottom of product). In any form, water is a dangerous contaminant. It can freeze and clog filters
and lines, and result in the loss of life or equipment.
(5) Microbiological growth. This growth consists of protozoa, bacteria, and fungi organisms that
grow in the fuel/water interface. These organisms hold rust and dirt in suspension, stabilize water emulsifications,
and cling to the sides of all containers. This causes erroneous readings in fuel systems, sluggish fuel control
operations, and sticking of flow dividers. The best method of controlling microbiological growth is good
housekeeping; however, FSII has proven to be an effective biocide.
(6) Fibers. This is caused by paper type filter cartridges, cloth and cotton waste. The fibers enter the
product flow when the filters burst or when new filters are placed into operation. After changing the filters, if
they had burst, recirculating the product through the filter/separator usually solves this problem. Left unchecked
the fibers can clog engine filters, flow lines, injectors, and carburetors.
(7) Commingling. Commingling is the contamination of a petroleum product with another petroleum
product. Some causes of commingling are: inadequate cleaning of lines, mishandling of manifolds, and leaks in
tanks or valves. Commingling can be negligible or serious, depending upon the product contaminated, the
contaminating agent, and the amount of contamination. Some of the effects of commingling are: loss of power in
fuels, increase in volatility, increase in gum content, formation of heavy sludge, degradation of thermal stability,
and increased water separation time.
b. Deterioration. The characteristics of a product change over time. The changes may be initiated or
hastened by the conditions of storage and are not normally observable by the