Good afternoon everyone I'm currently carried out work on water based cutting fluids used in our lathes and surface grinders. These machines are used about 2-3 times a month and the remaining time are left idle with the fluid being un-circulated in the holding tanks on the machines. I've checked the data sheets, Acop and COSHH for info from the HSE web site but cannot seem to find any clues has to what action I should be taking, apart from calling in a specialist company, which I think at present may be to early. So I hope someone may well be able to give me some idea has to what sort of time frame as to when we should either circulate the fluid or ever replace it. Other factors that may help are, the factory is quite a physical environment so working area temperature tends to be around 18-20 degree C but this does drop over night and at the weekends.

Hi http://www.hse.gov.uk/metalworking/legionella.htm This page looks to answer the question - "HSE guidance L8 “Legionnaires' disease. The control of legionella bacteria in water systems” recommends that the MWF storage and distribution system of lathe and machine tool coolant systems should be cleaned and disinfected every six months or more frequently if recommended by machine tool or fluid suppliers." Alan

It's like evolution, but in reverse. Despite 50+ years of research regarding the microbiology of MWFs, innumerable standards and guides, field investigations, commercial development in biocide production and use, cleaning agents, chemical, microbiological and physical test systems and protocols for regular microbiological examination, even the rather wispy washy HSE MWF pamphlet, we are advised to buy a fish tank pump and aerator from the pet shop! The available evidence - yes, there is plenty for those who want to read it - does not place Legionella anywhere near the top of the list of concerns from MWF. Nevertheless, this additional risk should not be overlooked, though it can be managed generically. Mr Packham will have us believe that lack of oxygen encourages bacterial growth, obviously without understanding of the complex ecology of MWF systems and the very high frequency of obligate aerobic species co-existing with facultative and obligate anaerobes, and sulphate-reducing species, or since the question is about Legionella, the fact that Legionella are aerobic and there is some chance that oxygenation might actually encourage and promote rather than inhibit Legionella growth. Many commercial MWF systems hold 50,000 litres of fluid managed centrally and distributed factory-wide. But if you really do want to ignore all of the knowledge and experience accumulated over the last 50 years or so, why not go ahead and make it worse, perhaps for the back street mechanic operating just a single lathe, and bubble air through the fluid in a crude attempt to increase average dissolved oxygen concentrations and simultaneously generate an aerosol that may be rich in the Legionella bacteria that are the cause of concern. I despair.

In response to Ian’s posting, his knowledge of microbiology is far superior to mine so I will not respond to his comments on this. However, my posting was based on many years involvement, firstly in the metalworking industry, where water-mixed metalworking fluid was often something that caused problems and secondly in the prevention of damage to skin due to exposure to metalworking fluids. The issue of tramp oil causing fluid degradation is well known, as is the issue of fluid degradation when machines stand idle for long periods. The concept of using aeration via a small aquarium air pump has been used successfully for a number of years to prevent the latter. It may be ‘low tech’, but it works and has saved employers who previously had to drain tanks and refill them considerable sums of money and time. Should we sneer at solutions that work and are cost effective, simply because they are low tech?

Mr Packham seems convinced that his home-spun aeration technique "works". With "many years involvement" in this field he will know full well the importance of evidence. Though many important advances begin with anecdotal evidence, the question to Mr Packham is simple. Where is the evidence? Throughout those "many years" surely there was time to address this innovation in a systematic way and, alone or with others, provide some evidence with which to support opinion that may otherwise distract or divert others from a more meaningful management of MWFs, preventing some of the more serious complications that can include skin problems, asthma-like illnesses, and at the most extreme, extrinsic allergic alveolitis, none of which can be prevented by a trip to the pet shop.

All this 'Mr' lark makes me feel like I'm in a courtroom!! My first thought was that legionella is not the primary concern with MWF's and that the guidance for regular bacterial checks and regular changes of MWF should also control any risk from legionella. History would not suggest incidences of legionella related illness linked to use of MWF (though I stand to be corrected). Just my thoughts but I'm no expert on sciencey based things.....Your Honour ;-)

Indeed Legionella are not recognised as a problem, but it was raised in the initial posting and Mr Packham claims to have a solution - an apparently off-the-wall and unproven solution for a problem that doesn't exist? It is also worth stopping for a moment or two to consider the use of MWFs. Are they not oxygenated already, by their circulation and recirculation during use? Indeed, one of the many earlier problems now managed by close containment and the use of baffles around lathes etc if that the damn stuff sprays everywhere. And obligate aerobes grow prolifically, through due to the complex micro-ecology of MWF systems these can co-exist with sulphate-reducing genera and other obligate anaerobes. Just about the only thing you don't find are goldfish. If this normal use of MWFs doesn't oxygenate them sufficiently, you can decide whether to get yourself off to the pet shop. And if that quaint addition doesn't then solve your problem, you know where to look for an explanation.

I did a quick google on aerating metalworking fluid to reduce bacterial growth and it seems that artificially aerating standing fluid is a well accepted method as long as the metalworking fluid does not foam. What a result! Thanks Chris, I wouldn't have thought of it but it seems like good advice.