Domestic water in commercial buildings. Reginald Brown

Transcription

1 Domestic water in commercial buildings Reginald Brown

2 Tap Drinking Domestic Mains Wholesome Sanitary Fresh Potable 2

3 Sterile Mains water myths Aerobic bacteria 3-34 cfu/ml as supplied to BSRIA - could be much higher out of the tap Pure 140 Ca, 6 Mg, 60 SO 4, 58 Cl, 36 NO 3 mg/l TDS ~ 450 mg/l Harmless Domestic water leaks probably cause more damage in buildings than heating and cooling system leaks. Insurance claims run into million of pounds each year. 3

4 Water quality reports Available free from water companies web sites 4

5 Domestic water system issues Corrosion and erosion Pipes needing replacement in less than 2 years Colonisation by bacteria and other microbes Pseudomonas Legionella Protozoa, filamentous fungi etc Joint failures Catastrophic release of water Unfortunately no time for joint failures today! 5

6 Corrosion 6

7 Corrosion risks Most domestic water systems use copper tube Copper pipework in new or refurbished buildings is at high risk of pitting leading to pinhole corrosion from: microbiologically influenced corrosion (MIC) disinfectant residues flux residues scale deposits If the water is allowed to stagnate!!! 7

8 Legionella guidance The draft of HSG 274 Part 2 The control of legionella bacteria in hot and cold water systems has a recommendation to use gas pressure testing to avoid a prolonged stagnation period prior to commissioning. If accepted by industry this may reduce the risk of some causes of pitting. The draft also suggests that weekly flushing of filled systems should be implemented to reduce stagnation and maintain the level of chlorine from the incoming supply. BSRIA experience is that weekly flushing unlikely sustain the mains chlorine level or be sufficient for the control of pitting corrosion. 8

9 Corrosion feature on outside 9

10 Typical nodule in base of pipe 10

11 Malachite and azurite crystals capping corrosion pit 11

12 Section of perforated pit Malachite & Azurite (mineral forms of basic copper (II) carbonate) Cuprite (a mineral form of copper (I) oxide) 12

13 Two sections from the same pipe 13

14 Pitting features 14

15 Linear spots 15

16 Micrograph of spots 16

17 Why black? 17

18 Basic SEM 18

19 Scanning electron microscope (SEM) micrograph 19

20 SEM Energy dispersive x-ray spectroscopy (SEM-EDS) 20

21 Chlorine Phosphorous Copper Oxygen Elemental maps around the perforation 21

22 Progress of corrosion pinholes Surface dirt and debris Carbon film Chlorination residue Biofilm Flux residue Stagnation Initiation of corrosion cell Pitting Perforation 22

23 Microbiologically influenced corrosion 23

24 Typical result of microbiological corrosion 24

25 Electron micrographs of microbiological corrosion features Underside of nodule Pitted surface 25

26 Assessing the cause of pitting It is more productive to look at pits that are still forming than a hole Well developed pits have similar composition irrespective of the original cause usually rich in chlorine Assessment of the root cause of pitting depends on looking at the general surface of the pipe (visually and by composition of scale) as well documentary evidence regarding the history of the system In-pipe endoscopy can help to determine the extent of the problem 26

27 Incidence of pinholes Most corrosion pin-holes occur in cold water pipes Most commercial building systems use pumped hot water circulation which avoids stagnation only the final connection to the tap will be subject to stagnation All erosion pin-holes occurs in hot water pipes on the return The root cause is excessive flow velocity in poorly balanced systems 27

28 Endosopy in 15 mm copper pipe using 6mm camera 28

29 Erosion 29

30 Turbulent erosion 30

31 Turbulent erosion 31

32 Erosion of scale 32

33 Cavitation 33

34 Bacteria 34

35 Bacteria and other microbes Microbiologically influenced corrosion Sulphate reducing bacteria Pseudomonads Pathogenic bacteria Pseudomonas aeruginosa Legionella 35

36 Endoscopy of 15 mm hot pipe 36

37 The source of the video 37

38 Draft legionella guidance A lot more background information on water systems but the principles of legionella control have not changed Recommendation on avoidance of stagnation is generally welcomed as mentioned earlier but some concerns on the safety and effectiveness of gas pressure testing Some concern also over the inclusion of chlorine as a candidate for continuous supplementary disinfection as it is not very effective against legionella and potentially detrimental to some system materials 38

39 Differences in risk assessment between legionella and pseudomonas aeruginosa Legionella Enters the system through the water supply Colonises parts of the system with favourable temperature and nutrients Risk assessment looks at the design, construction and operation of the water system Pseudomonas aeruginosa Enters the system from the outlets Colonises the outlets and fittings Risk assessment looks at the way the outlets are used and maintained i.e. people factors Specialist guidance in HTM 04-01: Addendum - Pseudomonas aeruginosa advice for augmented care units 39

40 Thank you! The new Illustrated Guide to Domestic Water Services will be published later this year and available as a free download to BSRIA members. BSRIA is also involved in the drafting of BS 8554 Code of practice for the sampling and monitoring of hot and cold water services in buildings also to be published later this year. Reginald.Brown@bsria.co.uk 40