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.
- TIP – searching on 'microbiological + dipslides' for the UK in your internet search engine should generate a list of suppliers of dipslides and information about their use.
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.
- <103 CFU/ml Good control. Bacteria are being maintained at low levels. No further action is required;
- 103 to <106 CFU/ml Reasonable control. Review control measures to ensure levels of bacteria remain under control. Risk assessment should specify action to be taken. Biocides and or cleaning may be indicated. If biocides are used, expert advice should be obtained, and the concentration of biocides should be monitored;
- > 106 CFU/ml Poor control. Immediate action should be taken in line with the risk assessment. Normally at very high levels draining and cleaning, should take place.
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:
- Working safely with metalworking fluids: A guide for employees
- Good Practice Guide for Safe Handling and Disposal of Metalworking Fluids