Quality Assurance Sampling (QAS) is a tool used by industry to ensure optimum fuel quality in bulk storage tanks.
Underground and above ground storage tanks are all susceptible to contamination from atmospheric conditions as well as inadvertent contamination due to poor housekeeping at site or by suppliers.
Most sites utilise paste on a dip stick which changes colour in the presence of water to determine the volume of water in a tank.
Some tanks in service stations and truck stops have Automated Tank Gauging systems that also have water detecting probes.
Both systems can give false readings due to microbial contamination emulsifying into the fuel allowing the contaminants and hydrocarbons to mix at the lower level of the tank from where the dispenser draws its fuel, nominal contamination drawn in to a chassis tank, generator or boat tank will rarely disable the engine and fuel system immediately, however with a diesel engines life expectancy of twenty thousand hours, every tank of contaminated fuel will decrease the life expectancy by hundreds if not thousands of hours.
Taking the example of a Hospital Emergency Generator that has water and microbial contaminants below the suction stub in the bottom of the storage tank, the generator will operate until fresh fuel is introduced which stirs up the contaminants and blocks the filters within thirty minutes, this scenario is real and could be prevented by Quality Assurance Sampling.