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Another Edinburgh' waiting to happen?
1 December 2012
The recent outbreak in Edinburgh of Legionnaires Disease was completely and utterly Inevitable says Colin Brown, Carter Environmental Engineers. AIthough the cooling tower industry is upping its standards, the problem isn't going to go away not until there are major changes to designs - and the regulations that supposedly govern them.
At some point, unfortunately, there will be 'another Edinburgh'. Not for a while, because everyone still has the big wakeup call ringing in their ears. Three people have died and around another 100 suffered from the Legionnaires outbreak in the south west of the Scottish capital, but initial tests to find who exactly was to blame at the cluster of cooling towers in the Wheatfield Road area have proved inconclusive- even though the first case was identified at the end of May.
As with any Legionella outbreak these days, this in itself is not a surprise. Somewhat more conclusive, sadly, was the sharp rise in chemical sales in the Edinburgh area as emergency chlorination procedures were rapidly put into place ahead of the arrival of the Health and Safety Executive.
The vast majority of water treatment companies (servicing around 75% of the UK's cooling towers) are good people, who clearly understand that the obligation they undertake to keep a tower safe is a moral decision as well as a commercial one. They are taking on the safety of the cooling tower system, and the well being of the people who work with it and those in the surrounding area. With all the bad publicity given to evaporative cooling towers it would be naive in the extreme to half-heartedly enter into the business of servicing them when you can find yourself culpable by law if you fail.
So, what's going wrong?
Despite all of the complexities of cooling tower technology, there is one adage that screams out loud and clear - and that is that if you can't get at something properly to maintain and clean it thoroughly, then you will never know if it is truly free from contamination and potential bacteria such as Legionella. Interesting then that one of the companies visited by the HSE was ordered to 'carry out thorough cleaning of one of its cooling towers and to provide access so that it can be inspected and maintained'.
It just cannot be a coincidence that every time we at Carter go out to site, the very first thing we are asked to do by the maintenance engineer is change the fillpack to one that can be removed. Even though the outbreak of Legionella at HP Bulmer in Hereford* was almost a decade ago (28 cases, two deaths), we have since continued to this day to win orders for retrofits where we convert hanging plate to removable block- not a major refit by any means.
The influx of attractive-looking, attractively priced cooling towers designed, for example, in the US and Europe, have brought about the rise of in-situ cleaning with no option for the fill-pack to be removed. At first, the theory behind these designs looks quite appealing, but as with many new products, the emphasis has all been placed at the front-end, with little or no regard for the servicing element.
However, the greyer than grey Acop L8 regulation (Approved Code of Practice and guidance) contains two very important words when it comes to the removal of the fill-pack. It says 'where practicable'. This allows those handling in-situ cleaning cooling towers to demonstrate via endoscopic equipment, for example, that their system is 'clean' - or so you'd think.
A camera might typically be passed down some of the flutes (the gaps between the corrugations on each plate pack), with the result that 'all is well' - but when you consider that even in a medium-sized cooling tower there are thousands upon thousands of flutes, it's hardly foolproof.
All of that said, everyone seems far too bogged down at the moment in only thinking about the fill-pack. One also needs to look at the water distribution system inside the tower- the trough and weir, or spray, or pan.
Emphasis should also be given to the cooling tower base tank. On many imported tower tanks, the drain is on the side, rather than as you'd logically expect, at the bottom. Predictably in this case the base tank will accumulate with water and sludge that can't be drained out properly. And then it stagnates. This has to be a big no-no, but according to Acop L8, you are not necessarily in the wrong, because cleaning is only 'where practicable'.
Demonstrating due diligence by way or record keeping (as required by local authorities and the HSE) one may show that the chemical makeup was correct and that scheduled cleaning took place, and that dip slides were in order. But, it may not have shown that a certain biocide drum ran dry, or that a dosing pump failed, or that a water filter was blocked.
We recently saw one cooling tower where there was a high Legionella count that came close to an outbreak, despite the fact that all the correct levels of chemicals were used (biocide, descalent, corrosion prohibiter). We also witnessed a case where two of three drums of biocide had run dry, but there were either no low-level alarms in place, or they weren't working. No shock then that at Edinburgh, one company was censured by the HSE for failing to devise and implement a sustained, effective biocide control programme for a cooling tower on its site.
So, how do we make things right?
Ideally, I'd advocate that all fill packs should be removable, but even for those that already are, it is best to apply full chlorination prior to removal, so that there is a full dispersion of chemicals. Importantly though, this should be carried out with the tower's fans on. Whilst one shouldn't scoff of course at health and safety issues, some are so engrossed in them that they almost seem to overlook the very reason for the cooling tower- to reject heat- so how about first checking that it is thermally efficient, as well as safe?!
When it is running, you are looking for a uniformed rainfall. If it is 'chuting' in just one or two areas it could mean that part of the distribution system is blocked. Without this consistently patterned rainfall, it is not doing its job. Turning the fans off allows for clear visual inspection - and stops you getting soaked!
When you do remove the pack you can usually see straight away if there is a problem. This could be the sight of biofilm, scale or sometimes contamination where the actual product produced at the plant has leached into the cooling tower and deposited itself on the pack.
Once converted to a removable pack, and with a suitable regime to monitor all of a cooling tower's water treatment-related elements, servicing costs can be reduced quite dramatically- and help build a far more efficient preventative maintenance programme. In typical in-situ packs, especially on cross-flow towers, the inlet louvre and the eliminator are all on the same profile, so if there is damage to any one part, you have to replace the lot - but once converted, they are all completely separate.
Gone, thankfully are the site visits we made when we'd discover a skip-load of empty Domestos bottles next to a cooling tower, with an operative proudly boasting that this was all the cleaning that was needed to 'keep the HSE away: But then only last month when we were called in to look at upgrading a cooling tower, we asked where the water treatment system is - to which the reply was: "Oh, do we have to have water treatment?"
Oh dear, this, in 2012. Hopefully this is a real rarity - and that by working with and giving maintenance personnel the right information and the right training - with cooling tower designs that do allow for key components to be removed for cleaning and inspection - then we can all ensure that the chances of 'another Edinburgh' are extremely unlikely.