Glossary
Air-conditioning - A form of air treatment whereby temperature humidity and air cleanliness are all controlled within limits determined by the requirements of the air-conditioned enclosure.
Artificial Water Systems - Any water system that has been constructed and does not occur naturally such as a hot water system.
Audits - The inspection and verification of an existing Legionella risk management system. This would normally involve the review of existing Legionella risk assessment reports and other documentation to ensure all critical risks are addressed and action plans are operational.
Biofilm - A community of bacteria and other micro-organisms, embedded in a protective layer with entrained debris, attached to a surface.
Calorifier - An apparatus used for the transfer of heat to water in a vessel by indirect means, the source of heat being contained within a pipe or coil immersed in the water. Usually cylindrical design, manufactured from steel / copper and mounted in the vertical / horizontal plane. Usually 750 – 2500 litres storage.
Chilled Water System - A type of air conditioning system that has no refrigerant in the unit itself. The refrigerant is contained in a chiller, which is located remotely. The chiller cools water, which is piped to the air conditioner to cool the space.
Chlorination - The process by which cold water storage tanks are cleaned of all dirt and debris. Chlorination should be carried out in accordance with BS6700 specification for the design, installation, testing and maintenance of services supplying water for domestic use and their curtilages.
Cold Water Service - Installation of plant, pipes and fitting in which cold water is stored, distributed and subsequently discharged.
Deadlegs - Pipes leading to a fitting through which water only passes when there is draw-off from the fitting.
Decontamination - The process of removing or neutralising pathogenic bacteria in a water or other system.
Dipslides - A dipslide is a means of testing the microbial content of liquids. It consists of a plastic carrier bearing a sterile culture medium which can be dipped in the liquid to be sampled. It is then incubated to allow microbial growth. The resulting microbial colonies are estimated by reference to a chart.
Direct Vent - Pulls outside air for combustion and vents combustion gases directly outside.
Disinfection - A process which destroys or irreversibly inactivates micro-organisms and reduces their number to a non-hazardous level.
Domestic Water Services - Hot and cold water intended for personal hygiene, culinary, drinking water or other domestic purposes.
Ductwork - Pipes or channels that carry air throughout a building.
Electronic Air Cleaner - An electronic device that filters out large particles and contaminants in indoor air. It then electronically pulls out tiny particles that have been magnetized, such as viruses and bacteria, drawing them to a collector plate.
Flushing - The process of draining and cleaning a cooling system, including all associated pipework.
Hot Water Services (HWS) - Installation of plant, pipes and fittings in which water is heated, distributed and subsequently discharged (not including cold water feed tank or cistern).
Legionnaires’ Disease - A severe form of pneumonia caused by Legionella bacteria.
Legionella - Type of aerobic bacterium which is found predominantly in warm water environments (singular of legionellae).
Legionellosis - Any illness caused by exposure to legionella.
Low use - Any outlet / appliance that has been identified as being used less than once a week. It is important that all of the domestic hot and cold water outlets and appliances are being used on a regular basis so that satisfactory turnover is achieved. If possible, low use outlets and appliances should be removed and the pipework services should be cut back and capped at the nearest live distribution positions. If the low use outlets and appliances cannot be removed, it must be ensured that they are thoroughly purged on a weekly cycle under a log book regime.
Micro-Organism - An organism of microscopic size including bacteria, fungi and viruses.
MCWS - Drinking water supplied from the Mains Cold Water Service.
Pasteurisation - Heat treatment to destroy micro-organism usually at high temperature. There is no British standard for pasteurisation but
Plume - The visible discharge of air and moisture from a cooling tower or other scooling system. This can include condensation and aerosols and as such represents a potential Legionella risk.
Point-of-use heater (in-line) - A water heater that is served off the mains supply or a down service and without an integral cold water storage tank facility. Normally electrically heated and with a small storage volume i.e. 15 – 50 litres. Normally serves single point or small number of WHBs / sinks.
Point-of-use heater (storage) - A water heater with an integral cold water storage tank facility. Normally at point of use or locally to the area it serves. May serve one or more rooms. Normally electrically heated. Variable storage volume i.e. 25 – 300 litres.
Pontiac Fever - A disease caused by species of legionella, an upper respiratory illness less severe than Legionnaires’ disease.
Risk Assessment - Identifying and assessing the risk from legionellosis from work activities and water sources on premises and determining any necessary precautionary measures.
Scale - Crystalline deposits that form on system surfaces or pipework. Scale normally results from a build up of unwanted minerals, usually calcium carbonate.
Scale Inhibitors - Chemicals used to control scale. They function by holding up the precipitation process and/or distorting the crystal shape, thus preventing the build-up of a hard adherent scale.
Sentinel Taps - For a hot water services – the first and last taps on a recirculating system. For cold water systems (or non-recirculating hot water systems), the nearest and furthest taps from the storage tank. The choice of sentinel taps may also include other taps which are considered to represent a particular risk.
Sludge - A general term for soft mud-like deposits found on heat transfer surfaces or other important sections of a cooling system. Also found at the base of calorifiers and cold water storage tanks.
Spa Pools (Spa Bath/Hot Tub/Jacuzzi) - A spa pool is a self-contained body of warm water designed for sitting in (not whole body immersion). It is intended for a small number of people to use at one time. The water is re-circulated and kept between 30ºC - 40ºC and is usually not drained between use and is continually filtered and cleaned. A hydro-jet circulation, with or without an air induction bubble system, is also used to agitate the water.
Stagnation - The condition where water ceases to flow and is therefore liable to microbiological growth.
Stratification - Stratification can occur in any calorifier or cylinder and there will be some temperature gradient across the vessel depending on the heat input and rate of draw. Temperature stratification can be overcome by the use of small pump units, which can circulate water from the top to the bottom of the hot water storage vessel.
Temperature Gauge - A suitable temperature gauge should be sited near to the calorifier / cylinder water supply outlet so that a quick visual indication can be made of the operating temperature. The temperature gauges should be checked and re-calibrated on a periodic basis.
Thermal Disinfection - Heat treatment to disinfect a system.
Thermostatic Mixing Valves - The hot water distribution temperatures that are required for the control and prevention of Legionella can lead to discharge temperatures in excess of 50º C. To prevent scalding injury to young children, the elderly and other vulnerable persons, action will be needed to limit water discharge temperatures.
Thermostatic mixing valves can be installed to reduce hot water temperatures to a safe level. The following maximum safe hot water temperatures are derived from the, “NHS Estates health Guidance Note ‘safe’ hot water and surface temperatures” 1998.
Showers 41º C
Wash basins and sinks 41º C
Baths 44º C
Ventilation - The process of supplying or removing air, by natural or mechanical means, to or from any space. Such air may or may not have been conditioned.
