Machine design tips to minimise risk of Legionnaires' Disease

Legionnaires' Disease is rare but, because it is so serious - fatal in a high proportion of cases (14 per cent of 300 annually in the UK) - it hits the headlines whenever it does occur. And one reason for its high profile is that there is usually a corporate body to blame for its presence, as the HSE (Health and Safety Executive) views most cases as preventable.

So companies that manufactures, install or use any form of water distribution system - including industrial plant, air conditioning, showers, taps and fountains - need to know the risks and responsibilities involved. Just being vaguely familiar with the term legionella and assuming that someone somewhere down the line deals with it will not be enough if the worst happens and it is your organisation that is found to be the source of an outbreak.

Fortunately, there is a lot of information available and a variety of experts ready and willing to advise on legal responsibilities, design tips, actions to take and things to avoid.

About Legionnaires' Disease

Legionnaires' Disease is caused by a strain of the bacterium legionella pneumophila, which lives naturally in ponds and lakes and particularly likes to multiply in man-made tanks and water systems. The bacteria thrive in water temperatures between 20 and 45degC; about 37degC is the optimum temperature for growth, particularly if the water is still for any length of time. Be aware of this if you have anything to do with:

• Piped water, especially hot water, in large buildings
• Air-conditioning and cooling systems, which have circulating water droplets in cooling towers and evaporative condensers
• Warm-water baths, including whirlpool baths, and shower heads
• Decorative fountains
• Any man-made water system that stores, reuses or recirculates water that can also be released as a spray or aerosol

People become infected by breathing in airborne contaminated water droplets - they cannot catch it from each other, or from drinking the infected water. Legionnaires' Disease is a form of pneumonia and the bacteria need to reach the lungs directly.

You may have heard that only 'vulnerable people' develop Legionnaires' and it is true that people are more likely to suffer if they are already in poor health, but this includes a very wide variety of people - any number of whom could be employees or customers. Long-term illness - asthma, diabetes, kidney disease, alcoholism, cancer - even if it is well managed, reduces the body's ability to fight infection. And so do certain types of long-term drug treatment and smoking. You are also more vulnerable to Legionnaires' if you are over 50.

Machine building and preventative measures

So what do machine builders need to know? There are regulations - mainly involving keeping the water temperature at less than 20degC or more than 60degC. The water supply should also be kept clean and moving so that it does not stagnate. All of this reduces the chance of legionella bacteria breeding - but it is important to appreciate that it is difficult to destroy this bacterium completely, so there is a legal imperative to ensure that all water systems in your premises are designed and made in such a way that they can be properly cleaned and maintained.

Any machinery built for processes that use water and create spray - or use water that could be released as a spray - will probably need a legionella risk assessment and in some cases a degree of treatment. Ideally, the designer or installer should provide information on the risks inherent in the equipment and processes - and advising that a risk assessment is carried out. And for the best kind of 'belt and braces' approach, it is an excellent idea to consult a specialist who can work on site with the machine builder's own experts.

HSE Approved Code of Practice

The key publication that should be on every company's shelf is the HSE's Legionnaires' Disease: the control of legionella bacteria in water systems. This Approved Code of Practice L8:2013 explains in minute detail what needs to be done to comply with health and safety law and keep water systems safe. As with most HSE ACoPs, 'following the guidance is not compulsory, unless specifically stated, and you are free to take other action. But if you do follow the guidance you will normally be doing enough to comply with the law. Health and safety inspectors seek to secure compliance with the law and may refer to this guidance.'

It is a 28-page document, but there are key paragraphs that explain the responsibilities of designers, manufacturers and installers - in summary:

This places a duty on any person who designs, manufactures, imports or supplies articles or substances for use at work, to ensure that they are safe and without risks to health at work and that any information related to the article or substance is provided.

The ACoP makes it clear that designers, manufacturers, importers, suppliers and installers of water systems must ensure that systems are designed and constructed to be safe when used at work; they must also provide adequate information for the user about the risk and measures necessary to ensure that safety at work. This information should be updated in the light of any new information about significant risks to health and safety, so that dutyholders can ensure relevant changes are made to their risk assessment and controls.

Also, manufacturers and suppliers of water systems must provide adequate information and instructions on their safe use. This should include information about those aspects of operation and maintenance that have a bearing on the risk.

Technical guidance

The technical guidance is in a separate document, HSG274, of which part three states the following about controlling other risk systems that may exist in industrial processes:

Any water system that has the right environmental conditions could potentially be a source for the growth of microorganisms, including legionella bacteria. There is a reasonably foreseeable legionella risk if the water system has a combination of the following factors:

• the presence of legionella bacteria in the system water, either introduced via the water supply and/or via external contamination;
• conditions suitable for colonisation and multiplication of the bacteria, for example, the water temperature in all or some parts of the system may be between 20-45degC;
• where water is stored or recirculated;
• deposits and materials that are a source of nutrients for the organism and support bacterial growth, such as contaminants from the surroundings or process including rust, sludge, scale, organic matter and biofilms;
• a means of creating and spreading breathable droplets (aerosols);
• the presence of susceptible people who may be exposed to those aerosols.'

Water must be kept free of unwanted bacteria and be maintained with scientific precision to ensure its safe use in any plant, equipment or climate control system, regardless of how small, large or complex, and wherever it may be used. Machine designers and machine builders have a significant role to play in minimising the risks, both in terms of design details and documentation.

More information about machine design tips to minimise risks of Legionnaires' Disease can be found at www.gwtltd.com, or contact Guardian Water Treatment with specific questions.