Legionnaires’ Disease

Background to Legionnaires’ Disease
Specific Legislation Relating to Legionnaires’ Disease
About Legionnaires’ Disease
The EcoCooling Approach to Managing Legionnaires’ Disease
Hygiene
Generic Risk Assessment
Generic Prevention and Control Plan

Background

It is estimated that there are 20 million evaporative cooling systems in the Western world. There has never been a documented case of Legionnaires’ disease associated with a wetted media evaporative cooler. Legislation in the United Kingdom is more stringent than anywhere else in the World. EcoCooling has developed the equipment and systems to comply with this legislation in a practical and relevant format.

Specific Legislation Relating to Legionnaires’ Disease

In addition to the Health and Safety at Work Act (HSWA), the Control of Substances Hazardous to Health Regulations (COSHH) and the Management of Health and Safety at Work Regulations (MHSWR) the HSC produce an Approved Code of Practice (ACOP) Legionnaires’ Disease: The control of legionella bacteria in water systems L8.

It is the legal duty of employers and the responsibility of the managers of premises to comply with the above.

Compliance with Legislation: The steps required in fulfilling statutory duties are: Completion of a Risk Assessment The preparation of a scheme for preventing or controlling the risk Implementation, managing and monitoring of precautions Maintenance of records Appointment of a responsible manager

About Legionnaires’ Disease

What is legionnaires' disease?

Legionnaires' disease is a type of pneumonia. It was named after an outbreak of severe pneumonia which affected a meeting of the American Legion in 1976. It is an uncommon but serious disease. The illness occurs more frequently in men than women. It usually affects middle-aged or elderly people and it more commonly affects smokers or people with other chest problems. Legionnaires' disease is uncommon in younger people and is very uncommon under the age of 20. About half the cases of legionnaires' disease are caught abroad. The other half are the result of infections acquired in the UK .

How do people get it?

The germ which causes legionnaires' disease is a bacterium called Legionella pneumophila. People catch legionnaires' disease by inhaling small droplets of water suspended in the air which contain the Legionella bacterium. However, most people who are exposed to Legionella do not become ill. Legionnaires' disease does not spread from person to person.

Where does it come from?

The bacterium which causes legionnaires' disease is widespread in nature. It mainly lives in water, for example ponds, where it does not usually cause problems. Outbreaks occur from purpose-built water systems where temperatures are warm enough to encourage growth of the bacteria, eg in cooling towers, evaporative condensers and whirlpool spas (tradename Jaccuzi) and from water used for domestic purposes in buildings such as hotels. Most community outbreaks in the UK have been linked to installations such as cooling towers or evaporative condensers which can spread droplets of water over a wide area. These are found as part of air-conditioning and industrial cooling systems.

What measures are there to control legionnaires' disease?

To prevent the occurrence of legionnaires' disease, companies which operate these systems must comply with regulations requiring them to manage, maintain and treat them properly. Amongst other things, this means that the water must be treated and the system cleaned regularly.

What are the symptoms?

• The symptoms of legionnaires' disease are similar to flu
• high temperature, feverishness and chills;
• cough;
• muscle pains;
• headache; and leading on to
• pneumonia, very occasionally
• diarrhoea and signs of mental confusion

How is it treated?

The illness is treated with an antibiotic called erythromycin or a similar antibiotic.

The EcoCooling Approach to Managing Legionnaires’ Disease

Evaporative Cooling System Design: The design of all EcoCooling equipment takes the ACOP guidance into account. This includes the following which would not normally be included on a standard installation of an evaporative cooling system:

• A water treatment system
• A process control system minimising build up of potential contamination
• Materials of construction which are corrosion resistant

System Management: Work Space Cooling provides all clients with the following:

• A fully documented risk assessment package
• A prevention and control system for water management and equipment care based on the following principles

Hygiene and Evaporative Coolers

EcoCooling believes that hygiene is the most important factor in providing a safe and secure system which provides compliance with legislation and peace of mind.

Hygiene

The maintenance of a clean and safe evaporative cooler is achieved by the following:

• Avoidance of stagnant water
• Low water operating temperature
• Avoidance of corrosion and scaling
• No production of aerosols
• Maintenance
• Use of a biocide or UV

Each of the above points will be detailed below

Avoidance of stagnant water: Since no dead legs exist in the system no stagnation occurs during normal operation of an EcoCooling evaporative cooler. When a unit is switched off the system automatically drains. A low level probe constantly monitors the water level when shut down.

When a system is first powered up the first operation is to empty the sump.

Low water operating temperature: The temperature of the water circulating in the evaporative cooler is approximately the “wet bulb temperature” of the air passing over the filters. In practice this means that, in a temperate climate, the water temperature rarely goes above 20 0C as shown even when the air on temperature exceeds 35 0C

It is generally accepted that Legionella is not a risk with water temperatures less than 20 0C

Avoidance of corrosion and scaling: To prevent corrosion all water contact surfaces are either plastic or non-ferrous. EcoCooling evaporative coolers measure the water usage. When the water reaches a set point , determined on commissioning according to the local water quality, the sump empties automatically and replenishes with fresh water. This has the effect of preventing scale and removing of contaminants filtered from the air. During this drain cycle the sump empties completely to assist in the removal of any sediment which may be present in the sump.

Use of Biocide: Growth of organisms filtered from the air is suppressed by supplying the evaporative cooler with water with a low level of biocide.

No production of aerosols: The design of the EcoCooling coolers is such that only pure water evaporation occurs as the air passes over the filters. This removes the mechanism for the transmission of infections such as Legionnaires’ disease

The maximum air velocity in an EcoCooling cooler is 1.9m/s. From the chart above it can be seen that the Munters maximum speed for avoidance of droplets is 3m/s. Thus a safety factor of over 50% is achieved.

Maintenance: By the implementation of a programmed maintenance system the standards of hygiene are continued to provide a safe and secure system. Detailed maintenance procedures are provided to all users.

Generic Risk Assessment

The end user is ultimately responsible for performing their own risk assessments. This generic document is intended to provide technical details to support these assessments.

Background

The purpose of this document is to provide an understanding of the legionella control in EcoCooling evaporative coolers. Government guidelines which provide the basis for both design and risk assessment are explained. The prevention plan demonstrates the EcoCooling approach

Government Guidelines

With reference to the HSE publication ACoP L8: Legionnaires’ disease: The control of legionella bacteria in water systems, the following is the section which describes general methods of legionella prevention

This document shall detail the approach taken to the above by EcoCooling in the design, commissioning, operation and maintenance of EcoCooling evaporative coolers.

Note: This document is not intended to replace a risk assessment produced as a requirement of HSE ACoP L8 – Legionnaires’ disease: The control of legionella bacteria in water systems

Prevention of Legionella in Evaporative Coolers

Note that the following only applies to EcoCooling evaporative coolers.

(a) Water Temperature

Monitoring of the water the circulating water temperature shows that with air on temperatures to the cooler up to 40 0C the temperature of the water in the sump does not normally exceed 20 0C in the UK climate. Data demonstrating this is shown in the chart below:

The above can be explained by the circulating water approaching the ‘wet bulb temperature’ of the air. In temperate climates the ‘wet bulb temperature’ rarely exceeds 20 0C and, in these rare instances, remains above this temperature for only a few hours.

Note that when the cooler is switched off the sump automatically drains. This prevents the water rising to ambient temperature which may be in the 20 0C to 45 0C range.

(b) Stagnation

During normal cooling operation the water continuously circulates. The design of the cooler avoids any dead legs and so stagnation does not occur. When the unit is not operating the sump automatically drains. The unit is fully self draining and therefore no stagnation is possible.

(c) Materials of Construction

With the exception of the filter pads all water contact surfaces are manufactured from plastic or non ferrous materials. The Munters CelDek filter pads are manufactured from a cellulose material which is treated with ‘anti-rot' salts to resist biological deterioration and to give high absorbency. It is a rigid, self-supporting product. The pads are examined during programmed maintenance and replaced as necessary.

(d) System Cleanliness

As water evaporates both the levels of dissolved salts and solids increase. The volume of evaporation is measured using four level probes and, when a set concentration is reached, the sump is completely drained removing both the water which is approaching the scaling point and any other sediment or particles in the system. The sump is then refilled using fresh, clean water.

Programmed maintenance includes cleaning of all water contact surfaces.

(e) Water treatment programme

Bromination can be added to provide additional microbiological security

Whilst Legionella is not considered to be a risk below 20 0C other organisms can grow in these conditions. The purpose of a biocide or UV is to prevent the formation of bio-films which could play a role in the support of legionella bacteria.

A brominator can be added which provides a residual minimum bromine level of 0.5 ppm in the sump.

The process control system, using a system of level probes to calculate the concentration of water is set to prevent scale formation.

(f) System Operation and Maintenance

Operating instructions are provided with each installation.

These include:

• Operating Instructions
• Brominator operating instructions
• Bromine level testing instructions
• EcoCooling can provide all chemicals and testing equipment required for the above.

A detailed maintenance procedure is used for the cleaning, sanitisation and validation of the operation of the coolers.

Summary

The overall level of risk is dictated by the quality of the air being cooled. It is the air that can provide the seeding of legionella and nutrients for growth. With clean air the units are very low risk when all of the prevention and control activities described are adhered to.

Generic Prevention and Control Plan