Legionella Control and HSE ACoP L8 — Water System Cleaning and Cooling Tower Compliance

Legionella bacteria thrive in water systems where conditions allow -- stagnant water, temperatures between 20 and 45 degrees C, and the presence of nutrients including rust, scale, sludge and biofilm. Legionnaires disease, caused by inhaling water droplets or aerosols containing Legionella pneumophila, has a fatality rate of approximately 10 to 15 percent. Employers and building owners have a legal duty under the Health and Safety at Work Act 1974 and the Control of Substances Hazardous to Health Regulations 2002 to control the risk from Legionella in water systems they are responsible for. HSE Approved Code of Practice L8 -- Legionnaires disease: The control of Legionella bacteria in water systems -- sets out how that duty is discharged in practice.

Legionella risk assessment and water treatment is specialist work requiring a competent person. This page covers the cleaning equipment implications of Legionella control programmes -- cooling tower cleaning, tank cleaning and system disinfection. It is not a substitute for a site-specific Legionella risk assessment.

The legislative framework

HSE ACoP L8 -- Legionnaires disease: The control of Legionella bacteria in water systems

ACoP L8 has special legal status. Failure to comply with an Approved Code of Practice is not in itself an offence, but in enforcement proceedings the failure to follow ACoP L8 is taken as evidence that the duty holder has not complied with their legal duties under HSWA 1974 and COSHH 2002. In practice, ACoP L8 compliance is the required standard.

ACoP L8 requires duty holders to identify and assess sources of risk, prepare a written scheme for preventing or controlling the risk, implement, manage and monitor precautions, keep records, and appoint a competent person to be responsible for the control measures.

HSG274 -- Technical guidance

HSG274 is the HSE technical guidance that supports ACoP L8. It is published in three parts: Part 1 covers evaporative cooling systems (cooling towers and evaporative condensers); Part 2 covers hot and cold water systems; Part 3 covers other risk systems (spa pools, vehicle wash systems, dental water systems, indoor ornamental fountains). The cleaning and disinfection procedures in HSG274 set the operational standard for Legionella control works.

COSHH 2002

Legionella bacteria are biological agents classified under COSHH. The risk assessment required under COSHH Regulation 6 must include the risk from Legionella in water systems. COSHH Regulations 2002

Cooling tower cleaning -- the highest-risk application

Evaporative cooling towers and condensers are the highest-risk Legionella source in most building portfolios. They generate aerosols -- fine water droplets -- that can travel significant distances in wind, exposing workers and members of the public to any Legionella present in the system water. ACoP L8 and HSG274 Part 1 require cooling towers to be cleaned and disinfected at least twice per year, with additional cleaning triggered by any indicator that the water quality has deteriorated.

The cooling tower cleaning process under HSG274 Part 1 involves:

Isolation of the tower from the system
Dosing with a biocide (typically sodium hypochlorite to achieve a minimum free chlorine concentration of 5 mg/l) and maintaining for a minimum period
Draining the system
Physical cleaning of all internal surfaces -- fill pack, basin, drift eliminators, distribution headers -- by high pressure washing to remove biofilm, scale and sludge
Refilling, dosing and monitoring before return to service

The physical cleaning stage requires pressure washing of cooling tower internals to remove biofilm and scale that biocide treatment alone cannot address. High pressure washing of fill pack and basin surfaces is a core element of a compliant cooling tower clean.

Equipment specification for cooling tower cleaning

Cooling tower cleaning is carried out in confined and restricted spaces with water management and biological contamination risk. The equipment requirements are:

Electric pressure washer -- petrol or diesel machines are not appropriate inside cooling tower structures due to exhaust risk in confined spaces and the potential for ignition of chlorine vapour from hypochlorite dosing. 240V or battery electric machines are the correct specification for internal cooling tower cleaning. View V-TUF electric pressure washers
Hot water capability -- hot water at 70 degrees C and above is effective against Legionella and biofilm. Hot water pressure washing of cooling tower surfaces after chemical dosing enhances the cleaning outcome. View hot water pressure washers
PPE for biological agents -- operatives carrying out cooling tower cleaning are potentially exposed to Legionella-contaminated aerosols during the cleaning process. FFP3 respiratory protection, eye protection, waterproof coverall and chemical-resistant gloves are required. A COSHH assessment specific to the tower and the cleaning operation must be in place before work begins.
Waste water management -- water drained from a cooling tower during cleaning is contaminated with biocide, Legionella and biological matter. It is trade effluent and must be managed and disposed of appropriately. Environmental Permitting guidance

Hot and cold water system cleaning -- tanks, calorifiers and pipework

HSG274 Part 2 covers hot and cold water systems in buildings -- cold water storage tanks, hot water calorifiers, water heaters, distribution pipework and outlets. The risk from Legionella in these systems arises from stagnant sections, incorrect temperature maintenance (cold water above 20 degrees C, hot water below 50 degrees C at distribution) and the accumulation of scale, sludge and biofilm that provides nutrients for bacterial growth.

Physical cleaning of cold water storage tanks is a core Legionella control activity. Tanks must be inspected and cleaned at appropriate intervals -- typically annually -- and whenever inspection reveals contamination. Tank cleaning involves:

Isolation of the tank from supply and distribution
Draining the tank
Physical cleaning of all internal surfaces by pressure washing to remove sediment, scale and biofilm
Disinfection with sodium hypochlorite solution
Rinsing with clean mains water
Refilling and testing before return to service

Confined space regulations apply to most cold water storage tanks -- entry requires a permit to work, gas testing, rescue provision and a competent supervisor. Confined Spaces Regulations 1997

Vehicle wash systems -- an often-overlooked Legionella risk

HSG274 Part 3 specifically identifies vehicle wash systems as a Legionella risk. Recirculating vehicle wash systems -- particularly those where water is stored in tanks and recycled through spray jets -- create exactly the conditions that support Legionella growth: water storage at ambient temperature, aerosol generation, biofilm in pipework and tanks. Duty holders responsible for vehicle wash facilities must include the wash system in their Legionella risk assessment and implement appropriate control measures.

For fleet operators and vehicle wash facility managers, this means regular cleaning and disinfection of wash water tanks, filters and distribution pipework -- not just the visible wash bay surfaces. Fleet and logistics hub

Sectors with significant Legionella risk

Related legislation and compliance

COSHH Regulations 2002 | Confined Spaces Regulations 1997 | Environmental Permitting | PUWER 1998 | Working at Height Regulations 2005

Trade accounts

V-TUF supplies electric pressure washers, hot water pressure washers and industrial vacuums to water treatment contractors, facilities management companies and building services teams carrying out Legionella control works across the UK.

Telephone: 01522 787978. Email through the contact page.

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Legionella Control and HSE ACoP L8 — Water System Cleaning and Cooling Tower Compliance