ASSE 12080 key terms

A gram-negative bacterium and the species most often linked to human legionellosis; it multiplies inside protozoa and biofilms in engineered water systems and reaches people through inhaled aerosols.

A severe form of pneumonia caused by Legionella bacteria, typically appearing 2 to 14 days after exposure to contaminated aerosols; older adults, smokers, and immunocompromised people are at highest risk.

A mild, self-limiting flu-like illness caused by Legionella exposure that usually resolves within a few days without treatment and does not progress to pneumonia.

The formation and release of fine water droplets or mist that can carry Legionella bacteria into the air and be inhaled deep into the lungs.

A community of microorganisms attached to a surface and embedded in a self-produced matrix; biofilm shields Legionella from disinfectants, heat, and shear forces and acts as a persistent reservoir.

A free-living amoeba or other single-celled organism that Legionella can infect and multiply inside; this relationship protects the bacteria from treatment and helps them persist in water systems.

The time between exposure to Legionella and the onset of symptoms, commonly 2 to 14 days for Legionnaires' disease and shorter for Pontiac fever.

A person whose immune defenses are weakened by illness, medication, or age, making them much more likely to develop severe Legionnaires' disease after exposure.

A consensus standard that sets minimum requirements for a building water management program to prevent legionellosis, including hazard analysis, control measures, and documentation.

A structured review of a water system to identify where Legionella could grow, multiply, or be aerosolized, and to decide which conditions need control.

A schematic showing how water enters, moves through, and leaves a building system, including treatment, storage, and points of use; it supports hazard identification and control planning.

A walk-through inspection and inventory of all water systems, equipment, and uses in a building, used to map hazards and confirm that drawings match actual conditions.

A section of pipe with no regular flow, allowing water to stagnate and temperatures to drift into the range that supports Legionella growth.

Low or no water flow in a system, which lets disinfectant residuals decay, sediments accumulate, and temperatures reach levels favorable for Legionella.

The length of time water resides in a system or storage tank; older water tends to lose disinfectant and warm toward growth-promoting temperatures.

Layering of water at different temperatures within a tank or system, which can create warm zones where Legionella grows even when bulk water appears adequately hot or cold.

The process of evaluating the likelihood and severity of Legionella exposure at each part of a water system and prioritizing controls where risk is highest.

A point, step, or procedure where a control measure can be applied to prevent, eliminate, or reduce a Legionella hazard to an acceptable level.

A documented, site-specific system of policies, procedures, and controls designed to prevent Legionella growth and transmission across all building water systems and devices.

A multidisciplinary group responsible for developing, implementing, and maintaining the water management program, typically including facility, engineering, maintenance, infection control, and safety representatives.

The designated individual accountable for day-to-day coordination of the water management program, including assigning tasks, tracking monitoring, and escalating problems.

A written, step-by-step instruction describing how a task is performed consistently, such as flushing, sampling, or disinfectant dosing, including who does it and when.

Records, drawings, procedures, and logs that demonstrate the water management program is designed, implemented, and maintained as intended.

The process of verifying that a new or modified water system is designed, installed, and operating according to specifications before it is placed into service.

A specific action, treatment, or design feature applied to prevent Legionella growth, reduce exposure, or keep a water system within established limits.

Maintaining hot water storage at 60°C (140°F) or higher and return water at 51°C (124°F) or higher to limit Legionella growth, while managing scalding risk at points of use.

A chemical agent such as chlorine or monochloramine used to kill or inhibit Legionella and other microorganisms in water systems.

Temporary or targeted dosing of chlorine at elevated concentrations to disinfect a system, often used for remediation after contamination or during commissioning.

A water treatment method that releases copper and silver ions to inactivate Legionella; effectiveness depends on water chemistry, contact time, and regular monitoring.

A filter installed at a fixture or showerhead to remove Legionella and sediment immediately before water is used, often used as a temporary or supplemental control.

Opening outlets or drains to move fresh water through piping, reducing stagnation, biofilm, and warm water conditions that support Legionella growth.

The step taken to fix a deviation, such as retreatment, repair, or flushing, and to prevent the problem from recurring when monitoring shows a limit was exceeded.

Routine measurement or observation of control parameters, such as temperature, disinfectant residual, or flow, to confirm that controls are operating within specified limits.

Evidence-based confirmation that the water management program, as designed and implemented, actually prevents or controls Legionella hazards under real building conditions.

Periodic checks, such as record review, sampling, or audits, that confirm the program is being followed and that control measures are achieving their intended results.

Predetermined parameter values that trigger investigation or corrective action; an alert limit signals a trend toward loss of control, while a response limit requires immediate action.

A general test of culturable bacteria in water that can indicate overall water quality and biofilm conditions, though it does not measure Legionella specifically.

A laboratory method that grows Legionella from water samples on selective media, providing confirmation and quantification but requiring days to weeks for results.

Reviewing monitoring data over time to detect gradual changes, such as rising water age or falling disinfectant residual, before they become compliance failures.

A structured review of the water management program against its own procedures and applicable standards to identify gaps and drive improvement.