1

An Introduction to Legionella Inspection and

Monitoring Of Hot and Cold Water Systems

2

Agenda

• Legionella needs• Cold water storage tanks• Hot water production and storage• Showers/little used outlets• TMV’s• Swan necks and Pigtails• Pump sets• Cleaning and disinfection• Alternative control strategies• Non-conformances• Log book audits

3

Legionella Needs• We have already spoken about the specific

needs of legionella bacteria that revolve around:• Temperature in the range 20 °C - 45 °C• Nutrients

• Iron• L-cystiene

• Habitats• Scale• Silt• Biofilm

• Oxygen

• Routine monitoring is designed to ensure we have the correct conditions at all times to prevent legionella growth.

4

Screen topreventIngress ofinsects etc

Sleeve

Screened air inlet(corrosion resistant mesh)

Access Cover

Insulation

WATER SUPPLY (WATER FITTINGS) REGULATIONS 1999

Flow Across tank

<24 hours storage

5

Cold Water Storage Tanks

• The following slide shows a multiple tank installation, how many of the poor design issues can you spot?

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7

Design Issues

• No insulation• Only two tanks have a lid vent (white mushroom)• The two nearer tanks have returning open vents

from calorifiers.• Common feed to service.• Draw off is close to the two nearer tanks• Stagnation will occur in far tanks.• Temperature of No1 tank, nearest, was 9 °C,

No15 tank, farthest was 19 °C

8

Corrosion in Tanks

9

10

Well Past Its Sell By Date?

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Sediment in tanks

• Significant levels of sediment in a tank can lead to bacterial hide-out.

• What is significant?• This will depend on the view of different

assessors.• It is important to establish historical trends

if possible.• Is the level of sediment in the next slides a

problem?

12

13

14

This is what they should be like

15

Feed and Expansion Tanks

• An F&E tank is most likely associated with the central heating system.

• This is likely to be a closed system at a temperature above that which legionella will be killed

• Can be disregarded, but noted, as significant to any legionella risk management issues

16

Hot water storage and production

• Storage calorifiers– Low pressure– Mains pressure

• Point of use water heaters

• Combi boilers

• Plate heat exchangers

• Tea boilers

17

Typical multiple installation

18

Fortic Tank

• Integral cold water header tank.

• Generally mains fed• Will the cold water

remain cold?

19

Gas-fired calorifier

Pressurised feed calorifiers(gas-fired)

20

Point of Use Water Heaters

• Are available in a range of sizes• Some have a body of stored water• Some have virtually no stored water• Some have an integral cold water header tank• They should deliver water at 50oC within one

minute.• Are prone to scale formation in hard water

areas.• Those which are dedicated tea boilers need no

further attention– Temperatures usually >80 oC

21

Larger Variety

• Mains fed• With integral header

tank• Serves multiple

outlets• Should deliver 50 oC

at the taps

22

Santon DFB

• Available in 25, 50 and 75 litre capacity.

• No cold water stored.• Has an optional TMV

fitted to the outlet.• Stores water at 60c.• If TMV fitted no

potential to check stored water temperature.

23

MARRALPoint of Use Heater With Minimum Storage Capacity (5 litres)

Medium Sized

• Mains fed• Medium size• Approx 5 litres stored

water

24

Small

• Mains fed• Little stored water• Easily adjustable• Users will almost

always turn down temperature

25

Combi Boiler

Direct Mains Supply

Water Storage Minimum or None

26

Plate heat exchangers

• Virtually no stored water

• Very quick response to peak demands

• Potential to scale up in hard waters.

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Tea Boilers

• Tea boilers produce water above 80c.

• Note their presence.• Can be disregarded

due to temperature.

28

Showers

• Are the heads and hoses being cleaned• Is the water hardness such that scale

deposits will form• Are they used regularly, ie at least every

week.• Are they TMV controlled

– Flushed weekly?

• Are they of the “safepurge” design– Dumps to drain prior to head opening to spray

29A selfpurging shower - discharges dead-leg water to wasteA selfpurging shower - discharges dead-leg water to waste

30

Little used outlets

• Something not used in a seven day period– Emergency showers– Emergency eye wash stations– First aid rooms

• Flush weekly– HTM twice weekly

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0

0.5

1

1.5

2

2.5

3

3.5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 23 24

WEEKS

LE

GIO

NE

LL

A l

og

10 c

fu/m

l Start Flushing

Stop Flushing

The effect of regular flushing on legionellae in shower water

32

TMV’s

• Primary use is to prevent scalding

• Target range 39 – 43c– HTM has specific ranges for specific

applications

• Sentinels must be checked monthly at both hot and cold pipework.

• Need regular maintenance

• Potential to scale on the cold side

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TMV’s

Typical Installation Calcium Deposits on Cold Side

34

Swan necks and Pigtails

• Swan neck• Can be found with

temperature gauges and pressure gauges.

• Are an effective dead leg.

• Have been implicated in legionella outbreaks

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Swan necks and Pigtails

• Pig Tail• Can be found with

temperature gauges and pressure gauges.

• Are an effective dead leg.

• Have been implicated in legionella outbreaks

36

Multiple Pump Sets

• Off line pumps are dead legs

• Need to alternate regularly

• Need to log that alternation is occurring

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Is this installation satisfactory?

38

Is this installation satisfactory?

• No• This is a twin tank installation• The draw off is such that the far tank will be drawn from

preferentially• Near tank thus may become stagnant.• Throttle back the valve on the near tank• Or move the draw off to a point central to the two tanks.• Is the diaphragm in the pressure vessel accessible?• Are the pumps used service/standby?• Is pump rotation recorded?

39

Cleaning & Disinfection• Systems should be cleaned and chemically or thermally

disinfected if:

• A routine inspection indicates a requirement

• the system has been altered or contaminated by maintenance activities,

• or after an outbreak or when inspection suggests it is necessary

• Chemical disinfection

• Usually to BS6700:2006 Chlorinate tank to 20-50 mg/l free chlorine and flush through ALL of the system and then leave to stand from one hour at 50 mg/l free chlorine or two hours at 25 mg/l depending on the initial concentration

• Thermal disinfection

• Circulate water at >60oC for at least one hour flushing each outlet at full temperature for at least 5 minutes.

• Caution required to prevent scalding

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Limitations of chlorine

• Biofilm• Not readily penetrated

• Raised temperatures • Causes chlorine to “flash off”

• Corrosive– Stainless steel

• May form carcinogens• Formation of tri-halo methane compounds

• High pH results in dissociation to non-effective molecules

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Relationship between measured free chlorine and microbiological activity

with varying pH A E Wright et al. 1989

0

5

10

15

20

25

5 10 15 20

Measured free residual chlorine (mg/l)

Mic

robi

olog

ical

ly a

ctiv

e ch

lori

ne (

mg/

l)

pH6

pH9pH10

pH8

pH7

42

Alternative disinfectants

• Chlorine dioxide– Continuous or one off– No pH constraints

• Isocyanurates– Liberates hypochlorous acid– Continuous for 90 days, DWi approved– Same pH constraints as sodium hypochlorite

• Hydrogen peroxide– Silver synergised

• Renal dialysis??– Continuous for 90 days, DWi approved, or one off

• Calcium hypochlorite– Liberates hypochlorous acid– Same pH constraints as sodium hypochlorite

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Alternative Control Methods• A number of alternative control strategies

exist other than the temperature control methods described earlier but with all these methods it is necessary to establish a control level , achieve the control level, ensure the control level and record these levels• COPPER AND SILVER IONISATION

• CHLORINE DIOXIDE

• OZONE and UV • Have no residual effect but can be useful as point of use

disinfectants. Contact your supplier for written guidance on the effective use of their product

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• Condition and cleanliness of electrodes (scale)• Calcium ions• pH of the water supply preferably <7.6

• Less effective against biofilm (UK BSRIA study)• Monitor silver and copper ion concn. at sentinel outlets• Copper 200 - 800 ug/l• Silver 20 - 80 ug/l

Silver and copper are not easily measured in the field

Copper and silver ionisation

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• A powerful oxidising biocide that is effective at levels of 0.5 mg/l.

• Good biofilm disruptor.

• Proven effectiveness against legionella.

• Maintains efficacy up to pH10

• Less reactive with organics compared with Cl2 and Br2

• Extensive range of pre-cursor methods available• Acid chlorite

• Ion exchange

• Tablets

• Dilute solutions

• Care needs to be taken as the Drinking Water Inspectorate permits a total oxidant level of <0.5 mg/l.

• HSE Acop minimum level is 0.1mg/l

• USEPA max limit 1.4mg/l

• Contact your supplier for written guidance on the effective use of their product

Chlorine dioxideChlorine dioxide

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Effectiveness and limitations of UV

• UV is an excellent disinfection process but may be UV is an excellent disinfection process but may be susceptible to reduction because of:susceptible to reduction because of:• Flow rateFlow rate• Type of lamp and temperatureType of lamp and temperature• Quality of water (transmission value)Quality of water (transmission value)

• Any suspended solids in the water will impact on transmissionAny suspended solids in the water will impact on transmission

• Type and quantity of organismType and quantity of organism

• Pre-filter is essentialPre-filter is essential

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UV water disinfection unitUV water disinfection unit

UV monitoring portUV monitoring port

Quartz tube enclosing UV lampQuartz tube enclosing UV lamp

Water inWater inWater outWater out

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UV Unit

Control panel

filter

Water supply

UV unit

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10μ filters

UV lamps

Hot water supply

Cold water supply

UV irradiated and control showersUV irradiated and control showers

ControlTest (UV irradiated)

50

UV irradiated shower

0

0.5

1

1.5

2

2.5

3

Weeks

Sterilised and UV on

UV off

UV on

Amoebae

Leg

ion

ella

log 10

cfu

/ml

51

Microbiological Monitoring - TVC

• Microbiological testing is not normally required unless:• There are concerns about water quality

• Taste or odour• Control measures are not being met, ie temperature out of

specification• Dip slides are not appropriate for hot and cold water

systems• Not accurate enough

• TVC analysis is not a measure of legionella activity

• All analysis should be undertaken by a UKAS accredited laboratory

52

TVC Action Levels

• E.coli, coliforms, pseumomonas ZERO• TVC’s at 22c, no more than 10x incoming

supply.– High levels indicate a potential for biofilm formation

• TVC’s at 37c, preferably <100cfu/ml– Bacteria that may possibly grow in the human body

• No absolute figure in either UK or EU guidelines for TVC’s at either temperature, even the above figures are not globally agreed upon.

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Actions following a high TVC result

• Firstly flush and resample, if still high take following action.

• Take a control sample at first point of entry into the building, if possible flame the outlets, is flaming not possible do the following:– Remove any fitments, diffusers etc degrease with isopropyl

alcohol.– Flush for 2 minutes.– Disinfect the inside and outside of the outlet with 1% sodium

hypochlorite for 2 minutes.– Flush for a further two minutes taking sample in mid flow.

• If results continue to be of concern then further system disinfection may be required.

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Microbiological Monitoring - Legionella

• Is generally not recommended, unless:– System temperatures cannot be attained as

previously defined.• Monthly testing is required until confidence in

control has been achieved.

– When a system is deemed to be out of control• Weekly testing until back in control

– When an outbreak is suspected.– Hospital wards with high risk persons present.

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Legionella Sampling

• Samples should be taken from:– Cold water systems

• Storage tank• Furthest outlet• Areas of specific concern

– Hot water systems• From the calorifier or the nearest outlet.• From the return to the calorifier or the last outlet.• From the base of the calorifier if a sample point is available• Areas of specific concern

• All analysis should be undertaken by a UKAS accredited laboratory.

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Legionella Counts – Actions Levels

• <100/litre - Under control

• 100-1000/litre - If only one or two samples are positive, system should be re-sampled. If a similar count is found again a review of the control measures and risk assessment should be carried out. If the majority of samples are positive disinfection should be considered but an immediate review of control measures should be carried out.

• >1000/litre - The system should be re-sampled and an immediate review of the control measures and risk assessment implemented to identify any remedial actions including possible disinfection of the system

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Non-Conformances• All out of specification results should be entered

onto a non-conformance log sheet.• A timescale for their rectification should be

given.• The name of the person responsible for the

corrective action should be stated.• The non-conformance should be signed off once

the corrective action has been taken and results are back within specification.

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Log Book Audits• Log books should be audited by “The

Responsible Person” quarterly.• There should be an audit sheet confirming

such has taken place and that all routine actions/results are in order.

• Special reference should be made to non-conformances.

• This is especially important when there is use of external contractors.

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The HSC Approved Code of Practice (L8) provides detailed guidance on the operation and management of hot and cold water systems - please consult this document for further guidance.

IF DOUBT - SEEK EXPERT ADVICE

AKVO Ltd – www.akvo.co.uk

Legislation & Legionella