To avoid the risk of corrosion, water used in the cleaning of stainless steel instruments should have a chloride concentration less than 120 mg/L and, for final rinse/disinfection, less than 10 mg/L Cl–. Chloride concentrations greater than 240 mg/L Cl– cause pitting to occur.
Heavy metals are generally toxic in low concentrations and, as far as possible, should be absent from water used to process items that will be used invasively. Tarnishing of stainless steel instruments, shown by blue, brown or iridescent surface coloration, occurs when heavy metal ions, such as iron, are present in the process water. In hot water (over 75°C) magnesium ions and silicates can cause similar discoloration.
Total Dissolved Solids
Total Dissolved Solids (TDS) cannot be removed with mechanical filtration or standard carbon filtration. A Reverse Osmosis system is one of the most effective means of filtering total dissolved solids from a water supply. With an RO system the TDS level increases on the high pressure side of the membrane as water permeates through the membrane to the low pressure side. The water containing the high level of TDS is flushed down the drain leaving the water with minimal total dissolved solids available for immediate use.
The pH of pure water is pH 7. Changes in the pH can be contributed to by the type of bedrock and environmental conditions the water has flowed through. The removal of chemical and mineral impurities from water through a process such as reverse osmosis can alter the pH of the water prior to use. Water that is not within the permissible range according to the guidelines can have an impact on the efficacy of the detergent and disinfection cycles of the decontamination process.
As with pH, the level of hardness depends upon the type of conditions that the water flows through, for example; water that has flowed through areas rich in peat is low in the minerals that contribute to hardness, whereas the chalk bedrock of East Anglia creates very hard water which in turn creates unwanted limescale deposits within the water delivery systems. Limescale can also provide a rough textured surface in which microorganisms are protected from manual cleaning and disinfection. In addition, high levels of hardness can interfere with disinfection efficacy. European Norms therefore require that ‘hard water’, as a superior challenge, is used in testing the efficacy of a chemical disinfectant.
Out of specification
Out of specification results observed when measuring the chemical purity of the water, generated by Reverse Osmosis Systems and used in Endoscope Washer Disinfectors, are usually an indication of a problem with the RO system. Problems can be caused by fouled, broken or exhausted membranes. In such instances it is recommended that the RO supplier is contacted to inspect the membranes and the RO system. In cases where the membranes are found to be clean and undamaged or where remedial action to the RO system does not resolve the problem, it is recommended to check the chemical purity of the incoming water prior to the RO system to check that there is not an issue with the incoming water source.
20/30 Labs asked an independent medical device validation company to assess the maximum air pressure that the ISO 15883 Dry Cabinet Surrogate Devices could withstand. Forcing air through the device would not give a pressure higher than atmospheric pressure, as the air simply passed through the device. To obtain a pressure greater than atmospheric pressure, individual sections of the surrogate device were isolated by clamping and air forced through. Each section of the device was tested by this method and was able to withstand the maximum pressure that the testing equipment could produce: 3.8 bar.