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Bacterial contamination

Fluid systems that contain water or water-mixes can become highly contaminated with harmful bacteria.

The bacterial contamination of fluids and associated machinery and pipework should be monitored and controlled. Direct means of measuring bacterial contamination should be used in conjunction with other checks on fluid quality, e.g. fluid concentration and pH. There are several ways of doing this. Microbiological dip slides are a simple way of checking bacterial contamination.

The risk assessment should cover how bacterial contamination of fluids is to be monitored. Factors to be taken into account include the system history, contamination risk, and fluid characteristics. For many systems and sumps, weekly checks (such as dipslides) will be required. The risk assessment may vary this period if the continuing control of bacterial contamination can be demonstrated. Checks (such as dipslides) will normally be required at some intervals to check continuing control.

A dip slide consists of a plastic carrier coated with a sterile culture medium, which is dipped into the liquid to be tested. It is then incubated to allow microbial growth and the resulting colonies are estimated by reference to a chart on which the density of the resulting colonies is compared to a reference chart to indicate the level of bacterial contamination. Results are expressed in terms of colony-forming units per millilitre (CFU/ml) of fluid.

The following values indicate what can be regarded as good, reasonable and poor standards of fluid management, and what action should be taken. Monitoring should be used to confirm your high standard of control, as well as indicating increased levels of bacteria at an early stage.

Your fluid supplier should be able to provide advice on the management of fluids to maintain them at optimum performance, and help reduce health risks.

Further information on metalworking fluids quallty:

Updated 2012-11-28