Glossary

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Legionella Risk Management Glossary (201kb, pdf)

Glossary A

Aerosols

Microscopic droplets or particles suspended in the air, eg. fog, smoke, or fine sprays.

Air conditioner

Or "refrigerated air conditioner" is a system that removes heat from air without the use of water. Indoor air is cooled by being blown over a refrigeration coil and redirected indoors. The refrigeration coil is then cooled externally by a fan or by natural convection using outdoor air. Examples of air conditioners are domestic refrigerated/reverse cycle integrated or split systems. Refrigerated air conditioners are not associated with cases of Legionnaires' disease.

Algae

Multicellular plants, occurring in water or moist ground, that contain chlorophyll but lack true stems, roots and leaves.

Amoebae

Protozoa able to change shape because of the movements of cell processes. They live in fresh water or soil or as parasites in humans and animals. Some amoebae can ingest Legionella and allow them to replicate whilst being shielded from the outside environment.

Anti corrosive agent

A chemical designed to inhibit or prevent corrosion in a cooling tower system.

AS/NZS 3666

Australian/New Zealand Standard 3666: Air handling and water systems of buildings - Microbial Control.
At present there are three parts to this standard:

• Part 1: Design, installation and commissioning
• Part 2: Operation and maintenance

Part 3: Performance-based maintenance of cooling water systems.

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Audit

An inspection and verification of a Risk Management Plan that involves review of documentation to ensure critical risks are being addressed and the risk management plan is being implemented.

Approved Auditor

A person qualified to audit Risk Management Plans for cooling tower systems. Under the Building Act 1993 definition, this means a person holding a current certificate issued under section 75GB of the Act by the Department of Human Services.

Glossary: B

Bacterial testing

Laboratory based testing to establish the concentration of bacteria in water. This type of testing will mainly utilize heterotrophic colony counts and does not include Legionella in total bacteria count.

Biocide

A physical or chemical agent that is capable of killing microorganisms including Legionella.

Biodispersant

A chemical compound added to recirculating water within a cooling tower system to penetrate and break down biofilm (see "Biofilm"), which may be present on the wetted surfaces of the cooling tower system.

Biofilm

A surface layer of microorganisms and other organic matter. It is usually combined with particulate matter, scale and products of corrosion.

Glossary: C

CFU/mL

A unit of measurement used in microbiology that indicates the number of microorganisms present in a water sample. It is measured by the number of colony forming units (CFU) present in a millilitre of the water sample.

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Glossary: D

Dead legs

Lengths of pipe ending at a fitting through which water flows only when the fitting is opened. These extra lengths of pipe contain stagnant water, which can cause a build up of bacteria and sludge.

Decontamination

A process that removes or neutralises pathogenic bacteria particularly Legionella.

DHS

Victorian Department of Human Services.

Disinfection

Is a process which

1. is intended to kill or remove pathogenic micro-organisms, including Legionella; and
   
   
2. in the case of a cooling tower system, consists of dosing the water of the system with -
   
   
   1. a chlorine-based compound, equivalent to at least 10 mg/L of free chlorine for at least one hour, while maintaining the pH of the water between 7.0 and 7.6; or
   2. a bromine-based compound, equivalent to at least 20 mg/L of free bromine for at least one hour, while maintaining the pH of the water between 7.0 and 8.5
      

Drift eliminator

A grid or grill-like arrangement of physical barriers located before the cooling tower exhaust - designed to minimize the drift emanating from a tower. Efficient eliminators should restrict the drift loss to less than 0.02 per cent of cooling tower recirculating water.

Glossary: E

Evaporative condenser

These units are similar in principle and in operation to cooling towers. Water is distributed directly over a bank of pipes, which contain circulating refrigerant or other fluids, but there is no fill as in cooling towers. These systems must be registered under the Building Act 1993 as cooling towers.

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Evaporative cooler

Evaporative coolers are also known as evaporative air conditioners, evaporative air coolers, and "swampies". They use water to cool outdoor air for use indoors (as opposed to a cooling tower, which uses air to cool water). Evaporative cooling is based on the same principle that the human body uses to cool itself down, with perspiration being evaporated from the skin by circulating air. Warm outside air is drawn into the unit through a series of wetted filter pads. Energy is removed from the air by the water causing a drop in temperature. The energy consumed by the water turns the water into vapour causing increased humidity in the air. The cool, humidified air is discharged indoors (where it is blown over the body causing additional evaporation or drying of perspiration from the skin and lowering of the body temperature). Doors/windows must be open to permit the forcing of this cooled air through the building.

Glossary: F

Fill

The structure located at the top of a cooling tower that is designed to create an extensive wetted surface area through which air passes.

Flushing

The process of draining a cooling tower, cleaning the basin, associated pipework and other parts of the tower.

Glossary: H

Heterotrophic colony count

Or "HCC" means an estimate of the number of viable units of bacteria per millilitre of sample water, using a laboratory based method such as the pour plate, spread plate or membrane filter test (also known as total bacteria count, total plate count or viable bacteria count test) method.

Glossary: I

Induced air crossflow cooling tower

This type of cooling tower has the fan mounted on one side of the tower. Air is induced through the fill; with the air passing in a cross flow manner past the falling water.

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Induced air counterflow cooling tower

This is the most commonly used type of cooling tower, where air is drawn through the tower fill by a fan located at the discharge of the cooling tower. Air enters the tower through louvres located above the basin perimeter and is drawn vertically through the tower in the opposite direction to the tower water flow.

Glossary: L

Legionnaires' disease

A rare form of pneumonia caused by the Legionella species of bacteria. Early symptoms of the disease resemble those of the flu, and include headache, fever, chills, muscle aches and pains and generally a dry cough, followed by shortness of breath. Other systems in the body can be sometimes affected resulting in diarrhoea, mental confusion and kidney failure.

Legionella

The bacterium responsible for causing Legionnaires' disease. They are a water-associated bacteria and infection is acquired through inhalation of infected aerosols. Legionella is widespread in the environment. It has been found in lakes, rivers, creeks, hot springs and other bodies of waters and soils.

Legionella count

Refers to the number of Legionella colony-forming units (CFU's) found in one millilitre of the water sample. The minimum level of detection is deemed to be 10 CFU/mL as per Australian/New Zealand Standard 3666: Air handling and water systems of buildings - Microbial Control. A count of less than 10 CFU/mL is regarded as not detected.

Legionellosis

Legionellosis (infection by any Legionella species) is an acute bacterial infection that can present as - Legionnaires' disease:

• This is the pneumonic form of the illness where the patient typically presents with severe pneumonia that frequently culminates in respiratory failure.
• Early symptoms are anorexia, malaise, myalgia and fever (flu-like).
• There is usually multi-system involvement with diarrhoea, vomiting, mental confusion, delirium and renal failure.

All cases of Legionnaires' disease must be notified to the Victorian Department of Human Services.

or -

Pontiac fever:

• The non-pneumonic form, presents mainly as a flu-like illness with spontaneous recovery and no reported deaths.
• It has a high attack rate (95 per cent) and outbreaks have been reported overseas.
• Pontiac fever has not been reported in Australia.
• It is not notifiable.

LRMP

Legionella Risk Management Project.

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Glossary: N

Nutrients

Any food source providing sustenance to an organism.

Glossary: P

PH

A term used to describe the hydrogen-ion activity of a system that provides a measure of the acidity or alkalinity of the water on a scale (range) between 0 and 14. Pure water has a pH of 7, acid solutions have a pH less than 7, and alkaline solutions have a solution greater than 7. For effective use of chlorine as a disinfectant pH should be maintained in a range of 7.0 - 7.8. Above this, and up to pH 8.5, bromine should be used if the pH cannot be easily adjusted.

PIC

Victorian Plumbing Industry Commission.

Plume

The visible discharge of air and moisture from a cooling tower. This can include condensation and aerosols. Usually most visible on cool mornings as condensation emanating from the top of a system.

PPE

Personal Protective Equipment.

Glossary: R

Risk management plan (RMP)

A risk management plan is defined in the Building Act 1993 as a document that identifies risks associated with the use of the system and that sets out the steps to be taken -

1. to manage the risks; and
   
   
2. to ensure compliance with any requirements relating to the system imposed by, or under the Building Act 1993 or the Health Act 1958.

Glossary: S

Scale

A crystalline deposit that can form on surfaces or pipework within the cooling tower system due to a build up of minerals (usually calcium carbonate). The water of the cooling tower system must be alkaline for scale formation to occur.

Scouring

The process of cleaning the internal piping of a cooling tower system.

Scum

A film of impurities that rises to or is formed on the surface of a liquid or is formed upon the surface of a solid object (such as the structure of a cooling tower).

Sludge

A build up of sediment that can be found in the basin or pipework of a cooling tower system.

Stagnant water

Pockets of motionless water within the cooling tower system that can allow microorganisms to grow.

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Spray drift

Aerosol emissions from cooling towers due to the fan forced or extracted air exiting the cooling tower.

Sterilisation

An act or process of destroying all forms of microbial life on or in an object.

Surfactant

A soluble surface acting agent that reduces surface tension between particulate matter and water.

Swampy

Commonly used term meaning "evaporative cooler".

Thermostatic mixing valves

Valves that mix the hot and cold water of the system to provide water at a predetermined temperature. These valves can overcome the necessity for long-term storage of tepid water and should be located close to the point of use.

Total Bacteria Count (TBC)

An estimate of the number of viable units of bacteria per millilitre of water under the conditions of testing (refer to "Heterotrophic Colony Count"). Note that a TBC does not test for the presence of Legionella.

Glossary: V

VWA

Victorian WorkCover Authority.

Glossary: W

Warm water system

Means a piped water system, including any thermostatic mixing valve, which is designed to supply water at a temperature of between 30°C and 60°C.

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