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Coronavirus And Legionella Control Testing

Advice for Legionella control during COVID-19 lockdown

The coronavirus is placing new challenges on our duty of care to minimise the risks from Legionella in our water systems on-site. Further restrictions on movement of people made last night will lead to further reductions in building occupancy increasing the risk of colonisation by Legionella.

We have been advised by the LCA (Legionella control association) & the HSE that all employers still have a duty of care to manage the risks from Legionella. The LCA website states:

 “While controls in place may need to be adapted to changing circumstances, duty holders must still be able to demonstrate control of risk to a reasonably practicable level.”

Loss of manpower due to social-distancing and self-isolation of staff could make this difficult. Our objective should be to deploy the resources we have in the best way to achieve the greatest reductions in the overall risk of Legionella becoming established in a building.

Below is a list of actions to be taken which will have the biggest impact in reducing risk in both hot & cold domestic systems and open evaporative cooling tower systems.

2. Domestic Hot & cold water systems

Buildings have already seen a significant decline in building occupancy and this is only likely to become worse. Water systems with dramatically reduced usage can quickly become hazardous if steps are not taken to mitigate this.

It is imperative that:

  • Flushing regimes are implemented whilst still in even partial operation to keep them from stagnating.
  • Where a flushing regime cannot be maintained, systems should be formally decommissioned and will need to be recommissioned before being brought back into use.

Actions required to keep domestic water systems safe

  1. Increased flushing regime & monitoring of turnover of water – Carry out building wide flushing of all domestic outlets on a weekly basis as a minimum. (2 minutes of flushing at each outlet on both hot & cold outlets)
  2. Take steps to measure water turnover within the building’s water systems. Estimated water usage can be obtained by taking water meter readings or performing drop testing of tanks.
  3. The above usage information should be used to establish the suitability of the current flushing regime.
  4. Reduce volumes of stored water where possible or as indicated by point 2 above. i.e. Where there are tanks/calorifiers balanced together consider taking some offline. 
  5. Increased Legionella sampling – Legionella sampling should be considered to check the effectiveness of the above controls. Contact Dantek for further advice.
  6. Where water is known to be stagnating consider leaving water systems charged with a Hydrogen peroxide and silver biocide (Such as Sanosil) to inhibit microbial growth.
  7. Systems that have been left without sufficient controls will need to be re-commissioned before being brought back into public use. Further guidance regarding re-commissioning is below.

3. Re-commissioning of domestic systems

Short Term – less than 4 weeks

Buildings left unoccupied for less than 4 weeks without the above controls in place.

  1. ℃.
  2. ℃ & 50℃ respectively.

Long Term – More than 4 weeks

Buildings left unoccupied for over 4 weeks without the above controls in place.

  1. Inspect cold water storage tanks for internal condition and clean if necessary
  2. Flush inlet pipework to cold water storage tanks and check for operation of all float valves.
  3. Open isolation valves on hot water calorifiers.
  4. Reinstate and check operation of secondary HWS circulation pumps.
  5. Open isolation valves on cold water storage tanks and any others which have been isolated as part of the shutdown.
  6. Bring booster sets back online and check they are primed.
  7. Carry out a chemical disinfection of the incoming mains, cold water storage tanks, calorifiers and all associated distribution pipework to all outlets. Dantek Disinfection procedures should be followed.
  8. Switch over any duty/standby pumps on the HWS secondary system.
  9. 3 days after the disinfection has been completed, take a representative number of samples and analyse for TVCC and Legionella.

 

4. Actions to reduce the risks – Open Evaporative Cooling systems

Maintain daily and weekly checks. 

  • Maintain the daily and weekly checks as an absolute minimum to ensure the tower is operating safely. This includes checking the following:
    • Dosage and control equipment is on and functioning correctly.
    • Adequate chemical stocks are in place
    • Control of primary Conductivity is satisfactory
    • Control of primary pH is satisfactory
    • Dipslide results remain satisfactory
    • Visual condition of the towers remains satisfactory.
  • Dantek will support where possible the maintenance of weekly cooling tower testing. The cooling tower should be shut down if weekly testing can no longer be completed for any reason or if there is a problem that can’t be solved immediately by the weekly testing.  
  • Consider increasing site stock of chemical to mitigate any future delivery issues.
  • If plant is controlled automatically and there is a risk of reduced demand steps to maintain circulation at all time should be taken.

5. Recommissioning of open evaporative cooling towers shut down:  

Cooling towers shut down for less than 1 week

  1. Visually inspect tower sumps, packing and drift and clean if required.
  2. Reinstate dosage and control equipment and check operation of chemical dosage pumps.
  3. Open any isolation valves and bring circulation pumps back online
  4. Check water quality (pH, TDS, Bromine/Chlorine levels) and adjusted so that it is within satisfactory limits.
  5. Once up and running take a dipslide and incubate.   

Cooling towers shut down for more than 1 week and less than 4 weeks

  1. The below should be carried out with w water treatment Engineer in attendance.
  2. Visually inspect tower sumps, packing and drift and clean if required.
  3. Reinstate dosage and control equipment and check operation of chemical dosage pumps.
  4. Check controller settings ad operation.
  5. Open any isolation valves and bring circulation pumps back online
  6. Check water quality (pH, TDS, Bromine/Chlorine levels) and adjusted so that it is within satisfactory limits.
  7. Once up and running take a dipslide and Legionella sample.  

Cooling towers shut down for more than 4 weeks

  1. Carry out full cleaning and disinfection of cooling towers systems as per Dantek Method statement
  2. Reinstate dosage and control equipment and check operation of chemical dosage pumps.
  3. Open any isolation valves and bring circulation pumps back online
  4. Check water quality (pH, TDS, Bromine/Chlorine levels) and adjusted so that it is within satisfactory limits.
  5. Once up and running take a dipslide and incubate.  
LTHW And Chilled Pipework Connections To An Office FCU

Advice for Legionella control during COVID-19 lockdown

The coronavirus is placing new challenges on our duty of care to minimise the risks from Legionella in our water systems on-site. Further restrictions on movement of people made last night will lead to further reductions in building occupancy increasing the risk of colonisation by Legionella.

We have been advised by the LCA (Legionella control association) & the HSE that all employers still have a duty of care to manage the risks from Legionella. The LCA website states:

 “While controls in place may need to be adapted to changing circumstances, duty holders must still be able to demonstrate control of risk to a reasonably practicable level.”

Loss of manpower due to social-distancing and self-isolation of staff could make this difficult. Our objective should be to deploy the resources we have in the best way to achieve the greatest reductions in the overall risk of Legionella becoming established in a building.

Below is a list of actions to be taken which will have the biggest impact in reducing risk in both hot & cold domestic systems and open evaporative cooling tower systems.

2. Domestic Hot & cold water systems

Buildings have already seen a significant decline in building occupancy and this is only likely to become worse. Water systems with dramatically reduced usage can quickly become hazardous if steps are not taken to mitigate this.

It is imperative that:

  • Flushing regimes are implemented whilst still in even partial operation to keep them from stagnating.
  • Where a flushing regime cannot be maintained, systems should be formally decommissioned and will need to be recommissioned before being brought back into use.

Actions required to keep domestic water systems safe

  1. Increased flushing regime & monitoring of turnover of water – Carry out building wide flushing of all domestic outlets on a weekly basis as a minimum. (2 minutes of flushing at each outlet on both hot & cold outlets)
  2. Take steps to measure water turnover within the building’s water systems. Estimated water usage can be obtained by taking water meter readings or performing drop testing of tanks.
  3. The above usage information should be used to establish the suitability of the current flushing regime.
  4. Reduce volumes of stored water where possible or as indicated by point 2 above. i.e. Where there are tanks/calorifiers balanced together consider taking some offline. 
  5. Increased Legionella sampling – Legionella sampling should be considered to check the effectiveness of the above controls. Contact Dantek for further advice.
  6. Where water is known to be stagnating consider leaving water systems charged with a Hydrogen peroxide and silver biocide (Such as Sanosil) to inhibit microbial growth.
  7. Systems that have been left without sufficient controls will need to be re-commissioned before being brought back into public use. Further guidance regarding re-commissioning is below.

3. Re-commissioning of domestic systems

Short Term – less than 4 weeks

Buildings left unoccupied for less than 4 weeks without the above controls in place.

  1. ℃.
  2. ℃ & 50℃ respectively.

Long Term – More than 4 weeks

Buildings left unoccupied for over 4 weeks without the above controls in place.

  1. Inspect cold water storage tanks for internal condition and clean if necessary
  2. Flush inlet pipework to cold water storage tanks and check for operation of all float valves.
  3. Open isolation valves on hot water calorifiers.
  4. Reinstate and check operation of secondary HWS circulation pumps.
  5. Open isolation valves on cold water storage tanks and any others which have been isolated as part of the shutdown.
  6. Bring booster sets back online and check they are primed.
  7. Carry out a chemical disinfection of the incoming mains, cold water storage tanks, calorifiers and all associated distribution pipework to all outlets. Dantek Disinfection procedures should be followed.
  8. Switch over any duty/standby pumps on the HWS secondary system.
  9. 3 days after the disinfection has been completed, take a representative number of samples and analyse for TVCC and Legionella.

 

4. Actions to reduce the risks – Open Evaporative Cooling systems

Maintain daily and weekly checks. 

  • Maintain the daily and weekly checks as an absolute minimum to ensure the tower is operating safely. This includes checking the following:
    • Dosage and control equipment is on and functioning correctly.
    • Adequate chemical stocks are in place
    • Control of primary Conductivity is satisfactory
    • Control of primary pH is satisfactory
    • Dipslide results remain satisfactory
    • Visual condition of the towers remains satisfactory.
  • Dantek will support where possible the maintenance of weekly cooling tower testing. The cooling tower should be shut down if weekly testing can no longer be completed for any reason or if there is a problem that can’t be solved immediately by the weekly testing.  
  • Consider increasing site stock of chemical to mitigate any future delivery issues.
  • If plant is controlled automatically and there is a risk of reduced demand steps to maintain circulation at all time should be taken.

5. Recommissioning of open evaporative cooling towers shut down:  

Cooling towers shut down for less than 1 week

  1. Visually inspect tower sumps, packing and drift and clean if required.
  2. Reinstate dosage and control equipment and check operation of chemical dosage pumps.
  3. Open any isolation valves and bring circulation pumps back online
  4. Check water quality (pH, TDS, Bromine/Chlorine levels) and adjusted so that it is within satisfactory limits.
  5. Once up and running take a dipslide and incubate.   

Cooling towers shut down for more than 1 week and less than 4 weeks

  1. The below should be carried out with w water treatment Engineer in attendance.
  2. Visually inspect tower sumps, packing and drift and clean if required.
  3. Reinstate dosage and control equipment and check operation of chemical dosage pumps.
  4. Check controller settings ad operation.
  5. Open any isolation valves and bring circulation pumps back online
  6. Check water quality (pH, TDS, Bromine/Chlorine levels) and adjusted so that it is within satisfactory limits.
  7. Once up and running take a dipslide and Legionella sample.  

Cooling towers shut down for more than 4 weeks

  1. Carry out full cleaning and disinfection of cooling towers systems as per Dantek Method statement
  2. Reinstate dosage and control equipment and check operation of chemical dosage pumps.
  3. Open any isolation valves and bring circulation pumps back online
  4. Check water quality (pH, TDS, Bromine/Chlorine levels) and adjusted so that it is within satisfactory limits.
  5. Once up and running take a dipslide and incubate.  
Children Washing Hands At School

Legionella control case study at a large boarding school

Dantek have provided legionella control services to Marlborough College for a number of years, below is a case study about how we work together to ensure ACoP L8 compliance and the safety of the students and staff.

Since its establishment in 1843 by a group of Church of England clergymen at the Castle Inn at Marlborough, Marlborough College has never been frightened of change. 

In its recent history, numerous academic initiatives have been fostered at the College including, Business Studies, SMP Maths, Combined Science, Pre-U examination syllabuses and the teaching of Arabic and Chinese. In 1968 Marlborough was one of the first of the traditional boys’ boarding schools to admit girls into the Sixth Form.

In 1989, the College became fully co-educational with the admission of girls into the Lower School and with the establishment of the first of the all-girl boarding houses.

Today the College caters for 936 pupils (of which just over 40% are girls) and the great majority of whom (98%) are boarders.  The remaining four “Out-College” houses accommodate 13-16-year-old boys, plus a mixed Sixth Form of both girls and boys.

School size: 201-500 employees

Based at: Marlborough, Wiltshire

The support Dantek provides

As a school, Marlborough College provides care for a large group of students most of which board on site, this means that they must adhere to strict health and safety guidelines. One of these areas is the need to protect students and staff from potential Legionella infection. Dantek has worked with the school for many years ensuring they comply with all regulations thus providing a safe environment for their students to thrive in.

As part of their on-going activity, Dantek engineers monitor the water quality, carry out remedial work and run regular testing and Legionella risk assessments. The College compliance team benefit from using Dantek’s electronic logbook which saves time and helps them keep on top of the various requirements. Dantek has provided a long-standing service to the college and act as part of their team which supports the quality of environment and interaction required by the College.

What does the client say?

We caught up with Kelvin Neale, M&E and Energy Manager at Marlborough College to find out how he views working with Dantek;

How did you hear of Dantek?

I have worked at Marlborough College for 8 months so Dantek were already in place when I joined. However, I did work with Dantek through another employer. I can certainly say that Dantek are known for their sound reputation in the industry.

What are the most important elements you look for in a contractor?

The most important elements for me are timely communication and a conscientious, effective manner. Due to the nature of the work Dantek provide, I also look for clear paperwork and accurate paper trial. We do consider the price, but it is not the only factor. When it comes to compliance, we must make sure we are choosing the right supplier who has the knowledge and systems which we require.

What do you like about working with Dantek?

I am very happy with their work in general. Three things stand up for me in particular:

  1. All engineers are professionals and knowledgeable, DBS checked and employed directly. They will always provide a service that goes beyond their contractual requirements and nothing we ask is ever an issue.
  2. The level of knowledge and expertise the company holds is impressive, they clearly know their stuff. I am also very impressed with the fact that on the rare occasion when they come across something they don’t know; they will go away to research for the right solution. It really demonstrates how competent they are and allows me to trust their advice implicitly.
  3. The electronic logbook is helpful and saves me a lot of time. It means I always have the data I need available to me and we never miss any tests and activities we need to complete.

How do they stand out against the competition?

As mentioned before, Dantek has a strong reputation in the industry. I think the main elements that make them stand out for me are as follows:

  1. The concise and timely completion of every job
  2. The electronic logbook which allows me to stay on top of compliance requirements, documentation and paperwork
  3. The level of knowledge and expertise they demonstrate about water treatment and legionella control

 

Cleaning And Chlorination Of Cooling Tower

Cooling tower water treatment – FAQ’s

What do I need to do if I am responsible for a cooling tower?
The first step is to carry out a Legionella Risk Assessment, it will need to be conducted by a competent water treatment professional with expertise in cooling towers. The risk assessment will form the basis of control measures put in place to reduce the risk of legionnaires’ disease.

You will also need to register the Cooling Tower with your local authority.

(The Notification of Cooling Towers and Evaporative Condensers Regulations 1992). These Regulations require employers to inform their local authority, in writing, if they operate a cooling tower or evaporative condenser and include the location of the tower to be used in case of an outbreak of Legionnaires’ disease. It is also a requirement for employers to notify when cooling towers are no longer in use. Notification forms are available from your local environmental health department.

https://www.gov.uk/cooling-tower-notification

What are cooling towers used for?
Cooling towers provide cooling for a wide range of industrial processes and air conditioning.

Cooling tower means a device whose main purpose is to cool water by direct contact between the water it holds and a stream of air.

Evaporative condenser means a device whose main purpose is to cool a fluid by passing the fluid through a heat exchanger which is itself cooled by contact with water passing through a stream of air.

Essentially, they are both arranged so that the air moves against the direction of the water.

The process of using evaporative cooling of water is widely used to deplete heat from air conditioning, refrigeration and industrial process systems. There are a range of evaporative cooling systems that use the evaporation of water to achieve this cooling effect and these include cooling towers and evaporative condensers. Open-circuit cooling towers are the most common and range in size from small packaged towers used in air conditioning and light industrial sites, up to large towers, including hyperbolic towers for heavy industrial uses.

Water boils at 100℃ and freezes at 0℃ and these changes of state from liquid to steam require an additional input of energy known as the latent heat of vaporisation.

The energy required to change 1 gram of water into steam is the highest of any known liquid which makes it particularly good as a cooling medium. As the water evaporates it takes a large amount of energy with it which cools the remaining liquid considerably.

Why cooling tower water treatment is needed?
The water used in cooling towers needs to be treated because impurities in the water cause the following problems all of which require actions for the system to run efficiently:

  • Scale
  • Corrosion
  • Suspended solids
  • Microbiological growth

It is important to have in place an effective water treatment programme to prevent the growth of legionella in the cooling water. A cooling tower water treatment programme should be capable of controlling not only legionella and other microbial activity but also corrosion, scale formation and fouling to maintain the system’s cleanliness. Appropriate water treatment may involve a range of chemical and physical techniques to control corrosion, scaling and fouling potential of the cooling water and to control microbial growth. Any water treatment regime must be monitored regularly to ensure they remain effective. The exact techniques that are required may vary significantly with different water supplies, the design of the cooling system and local operating conditions so it is important to engage a water treatment consultant to ensure the correct selection of control measures for your site.

How do you prevent legionnaires disease in cooling towers?
The first action is to identify and assess the sources of risk and appoint an individual who is managerially responsible for the system. This person must be trained and competent and must also have the authority and budget to act when necessary. The next step is to prepare a written scheme to include temperature monitoring, chemical treatment and any remedial works required to ensure compliance with current guidance. Once a scheme has been prepared it needs to be implemented, managed and monitored. Information must be held in a logbook so records are accessible and can be used to check the scheme remains effective. The records must be regularly reviewed, and any changes made to ensure effectiveness. Records must be kept for 5 years.

It is a legal duty to control the risk of exposure to legionella bacteria. As legionella bacteria are more likely to grow and proliferate in a cooling system fouled with sludge, scale and other deposits, maintaining system cleanliness and the water in it is an essential part of the control regime. The cleaning and disinfection frequency must be determined by a risk assessment and this should be based on inspection and the history of the water treatment control of microbial activity, scaling tendencies and other factors that may result in fouling of the system. In relatively clean environments with effective control measures, it may be acceptable to extend the period between cleaning operations, provided you can demonstrate that system cleanliness is maintained.

Water quality monitoring
The composition of the make-up and cooling water must be routinely monitored to ensure the continued effectiveness of the treatment programme. The frequency and extent will depend on the operating characteristics of the system. There are some checks which must be carried out weekly for example TDS and pH, while others are much less frequent for example legionella testing which is typically carried out quarterly.

Routine checks on cooling towers:

There are various checks which must be performed daily; these include a visual check of the cooling tower, check on the internal condition, dosage equipment and chemical drum levels check.

Every week the oxidising biocide levels, conductivity (TDS), pH, microbiological activity, pumps and softener must be checked and records updated in the logbook.

Why is scale a problem is cooling towers?
Scale is one of the four main issues found in cooling towers below are 5 of the key implications of scale:

  • Scale reduces heat transfer
  • Scale promotes corrosion
  • Scale promotes microbial growth for example legionella bacteria
  • Scale absorbs chemical treatments
  • Scale can obstruct pipework causing inefficiency and increased energy costs

Scale is the localised build-up of normally water-soluble inorganic hardness salts. Its formation is influenced by the concentration of calcium salts, pH, surface and bulk water temperatures and the concentration of the total dissolved solids (TDS). As an evaporative cooling system operates, the concentration of these various dissolved solids increases and the pH of the water tends to rise, which results in the scaling potential of the water increasing.

Scale formation results in loss of heat transfer, reduced flow rates and loss of efficiency and contributes to deposition. Legionella can be associated with such deposits. The scale protects the bacteria and so reduces the effectiveness of any biocidal treatment.

One or more of the following techniques generally control scale formation:

  • removing the hardness from the make-up water by pre-treatment, e.g. water softening
  • adding specific scale inhibitors that extend the solubility of the hardness salts and so prevent precipitation
  • acid dosing to lower the pH and alkalinity and reduce the scaling potential
  • limiting the system concentration factor to a range within which the hardness salts can remain soluble

What is TDS in a cooling tower?
Conductivity or Total dissolved solids (TDS) the quantity of solids dissolved in the water, measured in mg/l. These solids will typically include calcium and magnesium (sodium in softened water), bicarbonate, chloride, sulphate and traces of other materials. TDS indicates general water quality.

What are dipslides used for in cooling towers?
Dipslides are used to measure the level of bacteria. They are incubated at 30°C for 48 hours and bacteria will show as red spots. A comparison chart is used to assess the level of bacteria.

For further information about water treatment service contracts for cooling towers contact us to talk through how we can help keep your cooling tower running efficiently and compliant with the latest HSE guidance for Legionella control.

Checking Sample Legionnaires’ Disease With Microscope

Monthly statistics for Legionnaires’ disease Feb 2019

There have been 58 confirmed cases of Legionnaires’ disease since the start of this year (Jan 19). Click on the link below to read the full report issued by Public Health England which includes a full breakdown of where the outbreaks were geographically and also whether the disease was contracted while travelling both in and outside the UK or from the community.

Public Health England: Monthly Legionella report Feb 19

For clear advice about legionella prevention and control call Dantek to speak to an experienced water treatment professional.

 

 

Annual Cold Water Storage Tank Inspection

Top tips for inspection of cold water storage tanks

An annual inspection of cold water storage tanks is required to record the condition of the tank and the water within it.  It is also a requirement to check the temperature of stored water during the summer to ensure it remains below 20°C.

A trained Water Hygiene Technician must inspect the cold water storage tank and record the condition in the monitoring log book.  Any non-compliances are escalated in accordance with the chain of command stated in the control scheme and remedial actions carried out to ensure the tank remains in good condition within an appropriate timescale.

An inspection includes a check of both the inside and outside of the tank and the water held within it.  The lid should be tightly fitting and in good condition.  The insect and vermin screen on the overflow and warning pipes must be fitted and also in good condition.  The tank must be lagged which will help to maintain a constant temperature of the water and prevent it getting too warm or cold.  The surface of the water must not have a biofilm or show signs of stagnation.  The inlet and outlet of the tank should be opposing to also prevent stagnation.

Figure 1 below taken from page 26 of the HSG274 demonstrates the condition of cold water storage tanks and when action should be taken.  This traffic light system indicates actions to be taken and also the time frame in which they should be completed. 

Condition of cold water storage tanks and when action should be taken
Figure 1: HSG274 Legionnaires’ Disease p26

Regular tank inspection are an important part of a legionella control scheme because by preventing the habitat in which legionella bacteria can grow and proliferate you are ensuring the system will not provide the conditions suitable for harbouring legionella bacteria so therefore keeping your water system and ultimately your people safe.  

Coronavirus And Legionella Control Testing

Latest statistics on Legionnaires’ disease – Public Health England

The latest statistics for reported/notified cases of Legionnaires’ disease in December 2018 and a summary for the whole of 2018. In December there were 63 cases and there were 814 in 2018.

Interestingly, the graph indicates a rise in cases during the summer months. It also breaks down the figures into categories showing the source of infection. https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/776445/Monthly_LD_Report_December_18.pdf

 

HSE Logo

HSE Legionella e bulletin

The HSE published another useful round up of the latest news about Legionnaires’ disease. It includes details of the prosecution in December 2018 of Tendring District Council pleaded guilty to breaching Section 3(1) of the Health and Safety at Work Act 1974 and was fined £ 27,000  plus £ 7,500 costs, after a member of the public contracted Legionnaires’ Disease from a leisure centre hot and cold water system.

There is also a very useful link to download free factsheets about Rapid Microbiological Testing Methods produced by the WMS. Information about events coming up and the HSE Water Treatment Contractor Intervention Programme.

To read the full bulletin click: HSE Legionella Ebulletin

You can subscribe to the HSE Legionella bulletin’s and have them delivered directly into your inbox, ensuring you are kept up to date on Legionella control.

Legionella Sample Testing

Legionella testing – when do you need to take legionella samples?

Legionella sampling
UKAS accredited Legionella sampling

Do I need to take Legionella samples? 

It is a common misconception that taking Legionella samples is a requirement for Legionella control in domestic hot and cold water systems.  In fact, microbiological monitoring of domestic hot and cold water is not normally a requirement for compliance with current guidance. However, Legionella sampling would be required in high risk situations or in systems where current controls are shown to be failing. For example, if temperature control is consistently unachievable or disinfection concentrations are not satisfactory then alternative precautions should be carried out such as weekly microbiological sampling.

In high risk properties such as hospitals and health care premises, taking samples is a requirement. For specific guidance on microbiological monitoring refer to the BS 7592:2008 – Sampling for Legionella Bacteria in Water Systems – code of practice. 

It is very important to know that taking Legionella tests from domestic water systems does not achieve compliance with the HSE guidance document The Control of Legionella Bacteria in Water Systems ACoP L8.  The first step to compliance is to carry out a Legionella risk assessment and, then, to put in place a control scheme based on the findings of the risk assessment.

Whilst the ACoPL8 guidance are not law, they are enforceable under the Health and Safety at Work Act 1974 and the Control of Substances Hazardous to Health (COSHH) regulations. A Legionella risk assessment will define actions required for compliance with the guidance, and provide a schedule for any required ongoing monitoring e.g. temperature and biological monitoring if required.   

How long does it take to get a legionella sample result?

The most common question about legionella samples is how long will the results take?  Legionella tests must be analysed at an independent UKAS accredited laboratory. The incubation time for a Legionella test, using the standard culture method, is 10 days, so this is not a quick test to carry out. In the event of a Legionella positive result, the customer will be informed immediately by phone or email with advice about what to do next.

Different methods are available for Legionella testing which reduce the time to get a result from the lab. Some methods can produce a result in as little as 24hours. Please contact the Dantek office for further information if a fast turnaround is required. 

Where do samples need to be taken?

For sites where Legionella monitoring is a requirement in hot and cold water systems, sampling should be carried out in accordance with: BS 7592 Sampling for Legionella Bacteria in Water Systems. Depending on the complexity of the system, the actual number of samples will be worked out. It is important to ensure the sample is representative of the water flowing around the system and not just of the area downstream of the fitting; samples should be taken from separate hot and cold outlets rather than through mixer taps or outlets downstream of TMVs or showers. This will help to identify where any potential colonisation is and will help to inform on appropriate actions going forward.

A sampling plan should be put in place detailing the sampling locations and the type of sampling to undertaken. Whenever possible, samples should be taken from locations considered most likely to contain the highest numbers of legionellae.

Locations for Legionella samples in cold water systems

  1. From the point of entry of the mains or nearest outlet to the point of entry into the building
  2. Cold water storage tanks
  3. From nearest & furthest outlets (Sentinel points) on each branch of the system

Locations for taking Legionella samples in hot water systems

  1. From the nearest outlet to the calorifier
  2. From the base of the calorifier
  3. From the nearest & furthest outlets (sentinel points) on each branch of the system for single pipe systems
  4. From nearest & furthest outlets (sentinel points) on each loop of a circulating system

How is a legionella sample taken?

The scope and type of sampling (pre or post flush) should be set out in the sampling plan. Methods for the different types of sampling are detailed below.  If not specified pre-flush samples will be taken as standard.

A sample will be collected in a new, unused, capped, sterile litre sample bottle using aseptic techniques.  This minimises the chance of cross contamination of the sample and reduces the risk of a resample being required.  The bottles need to be labelled with the exact location where the sample was taken and the exact time and date. 

Dantek Technicians are trained to take the sample using aseptic techniques to prevent cross-contamination.  It is important that the correct sampling technique is used to achieve the most accurate results so that correct preventative actions are completed.

What is an aseptic technique for Legionella sampling?

Aseptic sampling techniques reduce the likelihood of contamination and poor sample results.

When taking samples, the technician must observe the following best practice:

  • Never touch the neck of the bottle or the inside of the lid
  • Ensure the bottle does not come into contact anything which may introduce contamination
  • Do not rinse the bottle out prior to the sample being taken
  • Minimise the time that the bottle is open to atmosphere
  • Only use the correct sterile bottle containing sodium thiosulphate or appropriate neutraliser.
  • Wash hands when sampling
  • Use hand sanitiser when sampling
  • Samples must reach the lab within 48 hours
  • Correct transport procedures should be followed
  • Ensure an air gap is left in the sample bottle

When taking a sample from a cold-water storage tank, the samples are to be taken from the centre of the tank where possible, taking care not to collect any solids.  Move the bottle forward through the water during sampling, ensuring water is only collected from in front of the bottle.

Steps to taking a Legionella sample:

  • Legionella samples must be taken in 1 litre sterile sample bottles containing sodium thiosulphate capable of neutralising up to 5ppm of free chlorine without effecting the bacteriological population.
  • Samples bottles, which are checked to ensure they are in date.
  • Samples bottles are checked before use to ensure that the lid seal is still intact.

Prior to removing the lid, the bottle should be marked with a permanent pen detailing the following information;

  • Customer
  • Site
  • Location of sample, building name, room location, cold water storage tank, calorifier, cooling tower sump, spa pool etc.
  • System identification, mains cold water, tank feed cold, domestic hot.
  • Pre or post-flush
  • Date & time of sample
  • Temperature of the water and/or chlorine dioxide reserve

How to take a pre-flush sample?

  • Do not disinfect the tap/outlet
  • Collect the sample immediately after the tap, or fitting, is opened, ensuring that the sample consists of only the first water which leaves the outlet.
  • Continue to fill the bottle leaving a 1 cm air gap at the top of the bottle.
  • Immediately replace the cap and invert the bottle several times.
  • Place the sample in a cool box and return to the office the same day.

How to take a post-flush sample?

  • Flush approximately 1 litre of water from the outlet.
  • Remove spray any inserts and flow directors from the outlet. It may also be necessary to remove and strainers and non return valves from TMV’s, strainers and solenoid valves.
  • Whilst wearing protective googles & gloves, make up a 200ppm solution of chlorine.
  • Clean the outside of the tap using the disinfectant solution.
  • Inject disinfectant solution into the outlet until it begins to run out of the tap using a wash bottle.
  • Descale and disinfect inserts and flow directors
  • Allow a two-minute contact time for the disinfection to take place.
  • Flush the outlet for 1 minute to remove the disinfectant.
  • Fill the sample bottle without adjusting the flow of water leaving a 1 cm air gap at the top of the bottle.
  • Immediately replace the cap and invert the bottle several times.
  • Place the sample in a cool box and return to the office the same day.
  • Rinse the outlet and surrounding area to remove any remaining disinfectant.

What should I do if the legionella sample comes back positive?

Firstly, don’t panic get in touch with Dantek and we will be able to guide you through the next steps to ensure you deal with the results in the correct way and to ensure your system is back under control as quickly as possible.  What action to take depends largely on the results and if this is the first positive result for the system.

If the first positive Legionella result is less than 1000cfu/ml:

If the minority of sample results are positive but less than 1000cfu/ml then arrange for a re-sample as soon as possible and review the control measures and risk assessment.

If the majority of the samples are positive but again with less than 1000cfu/ml then there is the possibility the system could be colonised at a low level.  Immediate review of control measures and risk assessment are needed and disinfection of the system must be considered.

If the 1st positive Legionella result is greater than 1000cfu/ml take the following action:

  • Arrange for a re-sample to be taken as soon as possible
  • Shut down any processes on the system where the positive sample was taken that can generate and disseminate airborne water droplets
  • Disinfect the system
  • Keep them shut down until sampling procedures and any remedial cleaning or other work has been done
  • Retest a few days after the disinfection and at frequent intervals afterwards until a satisfactory level of control is regained.
  • Review the risk assessment and control measures.

Following positive Legionella results a review of the Legionella risk assessment, control regime and record keeping/log books should be reviewed by checking the following:

  • They are current, up to date and accurate
  • That any remedial actions/recommendations have been completed
  • That the recommended control regime is in place. Identify the failing areas if there are any.
  • That good records are being kept of the activities undertaken
  • A record of the audit including any changes is placed in the log book

The question of whether to take samples or not can seem daunting however the key point to remember is taking samples will not affect levels of contamination on its own and does not necessarily offer compliance with the ACoPL8.  Ensure you keep your legionella risk assessment and control scheme up to date and seek advice from your water hygiene contractor.  If you have any concerns about Legionella samples, do get in touch with us as we are best placed to advice you about the Legionella control on your site.

Further reading:

http://www.hse.gov.uk/pubns/priced/hsg274part2.pdf

BS 7592:2008 Sampling for Legionella bacteria in water systems – code of practice

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