Hot and cold water systems in a building should be regularly monitored, operated, maintained at temperatures that do not lead to microbial growth such as harmful legionella bacteria.
This is usually achieved by maintaining a supply hot water temperature of at least 60°C from the heat source and or hot storage vessel, with the cold water below 20°C.
However, there is a possibility that legionella might start to grow in parts of the water system when infrequently used and is most likely to occur in pipes connected directly to showerheads or taps.
This is exactly what happened when buildings were closed due to the coronavirus pandemic. The unused water systems became a large dead leg with no water flow, thereby increasing the risk of legionella bacteria.
Therefore consideration should be given to keep the water flowing to avoid stagnation which could lead to biofilm formation.
This blog will look at the risk posed by little used outlets and how to correctly mitigate them.
What are little used outlets?
Any water outlet that is infrequently used can be referred to as a little used outlet. The definition of “infrequent use” may vary between applications and will depend not only on frequency and duration of use but also on other risk factors, such as water temperature and the vulnerability of the population.
The UK HSE’s HSG274 Legionnaires’ Disease: Technical Guidance Part 2, clearly states that any outlet “not used for a period equal to or greater than seven days” should be classed as a little used outlet. And as such, this circumstance will exhibit as a notable risk factor.
Little used outlets can occur in all buildings. They could range from outside taps, emergency showers, bathroom sink in a room not being used etc.
In the workplace, there may be outlets that are required for operational, welfare or safety purposes that do not receive regular and frequent use and/or areas that are temporarily out of use.
On the other hand, water systems in educational institutes may be under-used during the summer months due to the inoccupancy of the building.
There are likely to be void periods where a residential property has stood empty between tenants, sometimes for several weeks or longer.
This lack of use of the hot and cold water systems in such properties raises the possibility of increased levels of legionella bacteria and the associated risks from Legionnaires’ disease.
Managing the Risk in Little Used Outlets
The first step to managing legionella risk in the building is by getting a comprehensive risk assessment done by an independent assessor. A legionella risk assessment will identify and assess the risk of exposure to Legionella bacteria in your building.
When a little used outlet is identified, it must be managed.
The suggested hierarchy of measures that should be used to control the risk is:
1. Remove the water outlet
The first choice should be to remove the little used outlets – ensuring that all associated supply pipework is taken out and that no live dead-end pipework remains in situ.
According to HSG274 Legionnaires’ Disease: Technical Guidance Part 2 “Consideration should be given to removing infrequently used showers, taps and any associated equipment that uses water. If removed, any redundant supply pipework should be cut back as far as possible to a common supply (eg to the recirculating pipework or the pipework supplying a more frequently used upstream fitting) but preferably by removing the feeding ‘T’.
However, this may not be always practical.
2. Flush the Outlets
If an outlet cannot be removed, the outlet must be managed to ensure water does not stagnate in the system. This is achieved by flushing the outlets.
Flushing is the process of replacing stagnant water with the introduction of fresh cold water containing residual disinfectant. Flushed water carries away waterborne Legionella and dislodges biofilm lining the inside of the pipes and fittings, which harbours Legionella.
The flushing should be done in such a way to control the production of aerosols. Outlets should be fitted with a length of hose into the sink drain and be opened slowly to run without excessive splashing.
Normally a period of five minutes flushing per outlet will be sufficient.
Frequency of Flushing
The frequency of flushing depends on the susceptibility of the occupants of the building.
Little used outlets in general public areas such as schools, colleges, libraries, office buildings, must be flushed atleast once a week. The guidance document recommends that flushing is carried out at least weekly but also suggests that risk assessments should be used to determine if flushing is required more frequently.
In healthcare premises such as hospitals, nursing homes, and care homes where people with higher susceptibility would be present, the water outlets should be flushed atleast twice a week.
The risk assessment may indicate a need for more frequent flushing.
Water temperatures are equally as important when carrying out the five-minute flush, with any showers in the building being turned up as hot as the settings allow.
Hot water should reach a temperature no lower than 50°C after 1 minute’s flow; conversely, cold water should attain a maximum of 20°C (or below) after 2 minutes running.
Where there are concerns that temperatures during flushing are maintained between 20°C – 50°C then consideration should be given to obtaining a legionella sample and risk assessment of the site due to the increased risk.
Maintain Flushing Records
All actions should be recorded. Hard-copy or electric records should be recorded, including a list of the individual outlets flushed; the date, time and duration of flushing; biocide concentration; any other observations; and the initials of the person carrying out the work.
The person carrying out the flushing must fill out the flushing sheet and sign it.
Sheets to be stored in the site logbook along with any other relevant information observed at the time of flushing.
The key to managing risks associated with little used outlets is to get the design process right. Good design is essential to minimize the control measures and remedial works at a later stage.
Although disinfection protocols, sampling, remedial and possibly dosing the equipment installed will have a similar effect, the costs surrounding these alternative actions could quickly escalate. Hence, the concept of flushing out of a system should be the primary response.
Emphasis should be placed on maintaining a water flushing regime if the water systems are not going to be used for a while for any reason.
The team at Water Treatment Ireland Ltd could help duty holders and responsible person to effectively manage the hidden risks in the building and fulfil their duties regarding the control of legionella bacteria.
Contact our team for a free consultation today!