Akvo hot and cold water systems inspection
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Transcript of Akvo hot and cold water systems inspection
1
An Introduction to Legionella Inspection and
Monitoring Of Hot and Cold Water Systems
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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
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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.
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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
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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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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
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Corrosion in Tanks
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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?
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13
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This is what they should be like
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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
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Hot water storage and production
• Storage calorifiers– Low pressure– Mains pressure
• Point of use water heaters
• Combi boilers
• Plate heat exchangers
• Tea boilers
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Typical multiple installation
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Fortic Tank
• Integral cold water header tank.
• Generally mains fed• Will the cold water
remain cold?
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Gas-fired calorifier
Pressurised feed calorifiers(gas-fired)
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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
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Larger Variety
• Mains fed• With integral header
tank• Serves multiple
outlets• Should deliver 50 oC
at the taps
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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.
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MARRALPoint of Use Heater With Minimum Storage Capacity (5 litres)
Medium Sized
• Mains fed• Medium size• Approx 5 litres stored
water
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Small
• Mains fed• Little stored water• Easily adjustable• Users will almost
always turn down temperature
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Combi Boiler
Direct Mains Supply
Water Storage Minimum or None
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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.
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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
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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
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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
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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
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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?
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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?
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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
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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)
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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
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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
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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