Open-access content Thursday 28th April 2016 — updated 4.00pm, Tuesday 26th May 2020
5 May 2016 | By Chris Northey
Chris Northey explains the emerging threat posed by rising temperatures in cold water systems - particularly in modern buildings - and looks at possible solutions.
The past decade has thankfully seen few outbreaks of Legionnaire's disease, the potentially fatal form of bacterial pneumonia caused by the ingestion of legionella bacteria. This is largely because the hot water systems in the UK's buildings - once a common breeding ground for legionella - are now able to consistently maintain high enough temperatures to kill off the bacteria.
Legionella occurs naturally in water environments and flourishes under certain conditions. Temperature is the biggest factor in determining risk.
Between 25-50°C is considered high risk, however, the bacteria can still multiply between 20-25°C. Anything below 20°C and the bacteria can survive but will not multiply, while any temperature above 60°C kills it.
Keeping our hot water hot enough was historically the biggest issue when it came to combating legionella. Now, it is making sure our cold water stays cold that poses the real challenge.
Our buildings are now so well insulated that it is becoming difficult to maintain cold water systems below the 20°C temperature as recommended by the Health & Safety Executive (HSE). Water leaving the tank at, say, 20°C could rise to 25°C by the time it reaches an outlet - warmed rapidly by its passage through the thermal mass of the building and energy-efficient
materials such as cavity wall insulation and thermal plasterboard.
The problem appears to be even more acute in London, where water is already around 20°C when it enters buildings. This poses a real danger to human health. It is for everyone involved in the lifecycle of a building - from engineers, architects and contractors to building managers, FMs and occupiers - to work together to find a solution.
The letter of the law
Guidance on legionella control is provided in the HSE's Approved Code of Practice (ACoP) L8, published in 2013. Aimed at all dutyholders, including building and estates managers, ACoP L8 sets out all legal requirements in relation to legionella control, from the identification and assessment of risk to the implementation, management and monitoring of precautionary systems.
Although there is no specific law relating to the control of legionella as there is with asbestos and lead, ACoP L8 is still a legally binding document. If legionella is discovered in your building and you are found to be negligent in meeting the requirements set out in the HSE's code of practice, you could face a significant fine.
Estate managers must understand the guidelines set out by ACoP L8 to ensure that their buildings meet the necessary standards. They should also advise occupiers on the steps that can be taken to minimise risk - it is often the building users themselves who have little awareness of these issues and can unwittingly exacerbate the problem.
Rigorous monitoring of the temperature in the water systems (hot and cold) and taking samples from all outlets are the two essential activities to minimise the risk of legionella and ensure compliance with ACoP L8.
Building managers should be aware that it is not just older buildings that need constant monitoring. In fact, because of the extreme efficiency of modern insulation products, it is newer buildings that are often more prone to temperature issues.
Alongside temperature and effective water treatment, water movement can have a big impact on legionella risk, as stagnant water provides an excellent breeding ground for the bacteria.
In buildings that are unused over the weekend (schools, commercial offices, GP practices), there needs to be an adequate means of 'draw off' to stop bacteria growing.
One such option is to design the cold water system to keep water flowing at all times. Traditionally, one pump is used to boost water to the outlets as and when it is needed. What we are often doing now is including a return leg, with an additional pump to keep water circulating around the system at all times. This removes the risk of stagnation which, coupled with the correct water treatment, can significantly reduce the threat.
We can try to design out the problem, but too many times we see instances where the actual performance of a water system doesn't meet its 'as-designed' specification. This can be because the equipment is incorrectly installed or because the system isn't maintained to a high enough standard.
For those who are responsible for building management, it is vital that the correct steps are taken to make sure systems are performing as designed. This means regular planned preventive maintenance (PPM) and robust monitoring procedures - including continual sampling and testing of water from all outlets in the building.
Ultimately, if estates managers and others responsible for a building's lifecycle understand and follow the guidance set out in the HSE's code of practice, they can't go far wrong. Those who are not familiar with it should become so immediately - or they may face real problems.
Chris Northey is an associate director at building services & environmental design consultancy ChapmanBDSP