Feel the heat with legionella

Lack of compliance with HSE guidelines for the control of Legionella have been identified as one of the main reasons for a string of high-profile outbreaks in recent times. Geoff Hermitage looks at the steps and monitoring which should be taking place to minimise such outbreaks

WHILE the majority of activities described within HSE L8 guidelines for the control of Legionella are not difficult to grasp, sometimes putting them into practice proves difficult to manage effectively, particularly where those responsible are also trying to juggle with a plethora of other Health and Safety Legislation.

One common area of apparent conflict revolves around the requirement to minimise the risk of scalding on hot water systems. The Water Supply Regulations 1999 advise that the discharge temperature of hot water outlets should not exceed 43°C, particularly where there is a risk of full body immersion occurring (e.g. baths & showers). HSE L8 guidelines however advocate that hot water should be distributed at a minimum temperature of 50°C.

Installation of thermostatic mixing valves (TMV`s) local to the outlets is the usual compromise solution. To satisfy both regulations, the water is brought to the TMV inlet at 50°C minimum and is then reduced down by blending in a bit of cold water to allow discharge at the outlet below the 43°C maximum.

NHS estates have recently revised their advice to help clarify the situation and a new health and technical memorandum HTM 04-01 has been released to assist healthcare premises in the design and operational management of such systems.

However, TMV`s are often installed on a fit and forget basis - yet in practice they require regular monitoring and servicing to ensure discharge temperatures are maintained. Consider that a large hospital, for example, may have between 1000 and 2000 outlets with TMV`s fitted to minimise the scalding risk.  It then becomes no mean task to manage these effectively.

Many of the recent high profile cases of Legionellosis have been associated with wet cooling systems that have been poorly managed, either in terms of the water treatment programme itself or the operational management of the systems. Operators of wet cooling systems are required to register the presence of such systems with their local Environmental Health Department under the notification of cooling towers and evaporative condenser regulations 1992.

Under HSE L8 guidelines these systems should also be subject to ongoing treatment and monitoring to ensure that adequate control of microbiological growth, scale and corrosion is maintained.  A regular cleaning and chlorination programme is also required to minimise the risk of Legionella colonising the systems. 

Along with the large majority of commercial and industrial premises, many of the properties with wet cooling systems also have domestic type services with cold water storage tanks, calorifiers or other forms of water heater and showers present within.

The Health Protection Agency (HPA) advise with respect to Legionellosis: “The disease is spread through the air from a water source.  Person to person spread does not occur.  Breathing in aerosols from a contaminated water system is the most likely route of transmission.”  Poorly managed domestic systems supplying showers or other items of plant capable of generating aerosols can therefore also pose a risk should Legionella be present.

These systems can sometimes be overlooked in the overall scheme of control, particularly on busy industrial sites.  In properties such as hospitals and nursing homes where the occupants are at a higher risk in terms of susceptibility to Legionellosis these types of systems also pose more of a threat and need closer control and monitoring.

Much of the HSE L8 guidelines with respect to domestic type systems revolve around use of a temperature control regime where the cold water should be stored and distributed below 20°C and the hot water should be stored at a minimum of 60°C and distributed at a minimum of 50°C to the outlets.  A regular monitoring and inspection regime needs to be put in place to ensure that control temperatures are met and the plant remains in a clean condition.

Where this is not possible, alternative treatment regimes such as chlorine dioxide dosing or copper silver ionisation can be considered.  These treatment regimes usually have additional monitoring and control requirements however.

When considering control of Legionella it is important to consider all areas that may compromise the quality of the water in a system.  Poorly maintained filters and water softeners for example can act as ideal breeding grounds for bacteria that can then re-contaminate otherwise well maintained systems. 

A number of other areas that can sometimes be overlooked when considering items that could constitute a risk with respect to Legionella are highlighted in Table 1.

In deciding the best route to take with respect to Legionella control in a property, the first step is to undertake a Legionella Risk Assessment to ascertain the details of any water assets present on a site, their condition, mode of operation and their likely effects on the occupants of the building and the surrounding properties. 

The Risk Assessment should be carried out by a competent person.  Use of an external consultant is permissible and often desirable if no in house expertise exists.  The Risk Assessment remains valid for a period of two years but should be reviewed after one year to take account of any minor changes on site. 

If any major changes to the systems or the occupancy of the property occur, or in the event of an outbreak of Legionellosis the risk should be re-assessed immediately.

The risk assessment allows development of a written scheme for control of Legionella for the property and helps to identify any ongoing monitoring requirements and remedial works that may be necessary to bring the systems under the necessary level of control to minimise the risk of Legionella growth.

It is also important to develop a line of management for Legionella control.  A responsible person should be nominated to oversee the Control Programme.  He or she should have sufficient authority to ensure any tasks are carried out, but should ideally have a good working knowledge of the properties and systems. 

A chief executive may look an easy target to offload the responsibility onto, but often will not have the necessary working knowledge to ensure the tasks are carried out effectively.  A senior manager is often better placed to accept the responsibility.

The responsible person can engage suitable in-house staff and contractors to manage various aspects of the Legionella management programme but cannot simply delegate the entire responsibility to a third person and assume his duty is met. 

It is a requirement of the HSE L8 guidelines that any documentation relating to the Legionella control scheme is to be kept for a minimum period of five years.  Usual methods employed are by means of a local hard copy Legionella logbook or, in the case of a property with a large number of assets or multi-site operation, by an electronic database. 

Template logbooks and computerised management systems are available from a variety of sources.  BSRIA guideline document AG21/2000 is a common reference point for this area of management activity.

A copy of the written scheme for control of Legionella in the property should be included in the log book.
The Legionella management system should hold comprehensive records of monitoring results relating to the specific written scheme for the property together with any details of works carried out to the systems.  Most importantly it should also have recognised control limits for each item being monitored and an escalation procedure in terms of reporting and remedial actions if results fall outside the desired control parameters.

The accumulation of monitoring results alone, whilst providing evidence that the systems are being visited, does little in itself to minimise the risk with respect to Legionella.

Any personnel carrying out tasks relating to the Legionella control programme need to have undertaken appropriate training to ensure that they understand the implications of any tasks they are being asked to carry out.  The training can be carried out in-house by suitably qualified personnel, alternatively a variety of external consultants and associations provide suitable training courses aimed at bringing operators or managers up to the necessary level of awareness. Appropriate training records should also be kept within the management scheme.

The water treatment market has changed over the last twenty years and water analysis alone forms a small part of meeting today’s legislative requirements.  Appropriate water monitoring and control systems have become much more of a necessity particularly in tackling the control of micro-organisms such as Legionella.  This particular organism in all likelihood has always been there.  Our understanding of it has not; but we are catching up.

By Geoff Hermitage. Geoff is principal water quality scientist at STATS. He is a chartered biologist and member of The Water Management Society.