Legionella defence – harnessing plastic solutions for safer water systems

The disease, caused by legionella bacteria can be fatal, with the peril increasing with age. Craig Norman, Building Segment Manager at Aliaxis, outlines the dangers of a build-up of this bacteria and how plastic pipe systems are better equipped to combat legionella than copper or other metal pipes.

Over the coming decades our ageing water infrastructure will be upgraded with thousands of miles of new pipes installed. During this process there should be an increasing shift towards the specification of plastic pipes given the installation benefits of saving time and money, the health benefits, its durability and longevity to support cold and hot water.

Effective management of the legionella bacteria in water systems is critical to maintaining a healthy water supply and this bacterium can build-up when standing water is left and not flushed out of a plumbing system. Failure to do this increases the risk of the growth and spread of legionella and other biofilm-type bacteria. The parameters for, and control of, legionella fall under the Health & Safety at Work Act 1974.

Whilst consumers don’t tend to give legionella a second thought unless there is a local outbreak, most think the bacteria enters their body mainly through drinking tap water. However, infection can also happen when the bacteria is inhaled via water vapours from areas such as showers, spas, humidifiers and cooling towers too.

Legionella came to the forefront again this summer following the outbreak of the bacteria on the Bibby Stockholm barge, docked at Portland Port in Dorset, which had been refurbished to house 500 migrants. Around 40 migrants initially boarded the barge on August 7 – the day on which legionella was discovered.

Clearly, questions were asked about whether the right protocols were in place, particularly with an ageing and original plumbing system likely to have been in place on the barge. Experts will have examined whether the system had been sufficiently tested and treated; and if there were any ‘dead legs’ housing stagnant water – as this would provide the conditions for legionella bacteria to sit and grow, even after the system had been flushed.

Plastic pipes with their smooth inner core make it more difficult for biofilm to grow - any type of bacteria is more likely to form on a rough surface; therefore, plastic pipes, with their smooth inner bore, help to manage potential bacterial contamination of the water by eradicating such problems as scaling and corrosion. A metal plumbing pipe with a rough inner surface can create the conditions for bacteria, such as legionella to flourish and release into the water supply in harmful quantities.

Since the introduction of Polyethylene (PE) in the 1950s, there has been a debate around whether the material provides a better alternative to metal, particularly when it comes to the transportation of potable water. Whilst architects and contractors are increasingly turning to plastic pipes as the water delivery solution, the majority of the installed pipes in the UK market remain copper-led.

Plastic pipes can be a vital tool in combatting the risk of legionella and one of the main benefits offered is the element of temperature control. People assume that you need to heat water to extremely high temperatures to kill this and other types of bacteria, but boilers don’t need to be run at such high temperatures to do this.

Plastic pipework solutions can operate in temperatures up to 70°C for hot and cold domestic systems for which legionella bacteria is destroyed at 60°C. Water that is operating at 20-50°C can potentially provide the right environment for legionella to develop. It is important that systems operate at over 50°C, being stored at 60°C, but it is true to say that they are run hotter as a ‘belt and braces’ measure.

In contrast, water in metal pipes due to the nature of the material surface, can build micro-organisms and biofilms faster than a plastic pipe. This can lead to much higher temperature shocks and require harsh chemicals to clear the pipe of risk. Metal pipes can support usual operating temperatures of between 85°C and 95°C.

Plastic pipes offer several key advantages over metal ones. Most plastic pipes can resist chemicals present from purging and cleaning, in particular C-PVC pipes can withstand a variety of chemicals for longer periods of time or higher concentrations required by applications and /or maintenance of a building. However, in most cases plastic pipes require a limited use of chemicals to achieve a safe potable water supply.

Whilst there has been a growth in the sales of plastic systems in recent years, the majority of contractors and installers who have worked in the sector for decades tend to stick with what they were brought up on and that’s copper and metal pipes. Therefore, a significantly wider use of plastic will only come through the specification route.

The Government’s Health and Safety Executive (HSE) has published guidelines to combat the risk of being exposed to legionella from the water supply. The website provides information for employers and those controlling premises on the precautions that need to be undertaken to control the risk. The areas that need to be addressed are:

• Identifying and assessing the sources of risk
• Management of those risks
• To prevent or control any identified risks
• Keep and maintain the correct records
• Carry out any other duties you may have

The HSE states: “You or the person responsible for managing risks, need to understand your water systems, the equipment associated with the system such as pumps, showers etc, and its constituent parts. Identify whether they are likely to create a risk from exposure to legionella.”