Legionella and Fire Fighting Systems - Residential Sprinkler ...

LPCTBN 14 MAY 1999Loss Prevention CouncilBriefingTechnicalnotefor InsurersLEGIONELLA AND FIRE FIGHTING SYSTEMSThis Technical Briefing Note is part of a series of publications from The Loss Prevention Council. Technical BriefingNotes offer information and guidance for insurers and others on topical issues. They are intended to provide earlyadvice where attitudes and loss prevention measures are not fully established. They present an in-depth critical reviewof current knowledge and practice together with references and sources of further information. Where appropriateThe Loss Prevention Council will produce additional Notes on the topic, or more detailed reports.This Note has been prepared by The Loss Prevention Council. Further information on this issue can be obtained fromDr Richard Bailey at The Loss Prevention Council.CONTENTSPageLegionellosis 1Fire fighting systems 2Assessment of risk 3Control of legionella 3Conclusions 4References 4Further information 4SUMMARY• The term Legionellosis covers a group of diseases(which includes legionnaires’ disease, a form ofpneumonia) that can be contracted by inhalingwater droplets or aerosols containing bacteria fromthe genus legionella.• There are roughly 175 cases of legionnaires’ diseasein England and Wales per year, the mortality ratebeing about 10-15%. These cases are usuallyassociated with water towers for air conditioningsystems.• The operation of fire fighting systems (sprinklers,drenchers and ring mains) may create inhalablewater droplets. However, the conditions normallyfound within fire fighting systems are not thoughtable to support the growth of populations oflegionella.• The risk of catching legionellosis from a properlyinstalled and maintained fire fighting system isnegligible, although this risk may increase forprivate water supplies, for maintenance personneland in health care establishments.• LPC suggested control measures:• Incorporate fire fighting system into any existinglegionella monitoring system for the site.• Minimise production of aerosols during testingand maintenance.• Maintaining pipes and water storage tanks at

acterium can cause a mild fever (Pontiac fever) inotherwise healthy individuals. Other legionella speciesinclude L. micdadei (non-pneumonic Lochgoilheadfever) and L. feelei (pneumonia-type illness).There are roughly 175 cases of legionnaires’ disease inEngland and Wales per year, the mortality rate being about10-15%. Infections tend to occur in public buildings(hospitals, hotels, etc.) following contamination ofrecirculating and/or hot water systems such as airconditioning systems.Medical aspectsLegionellosis can be contracted by inhaling fine aerosols(clouds of fine droplets and particles) from a water sourcecontaminated with legionella. Potential aerosol-producingsources include running taps, showers, fountains, coolingtowers, whirlpool spas, and misting devices such ashumidifiers. If the aerosols are small enough (≤5 µm indiameter) they can pass deep into the lungs where theymay be deposited into the terminal air sacs (alveoli).Another (theoretical) route of exposure is breathing in ofwater whilst drinking. There is no evidence that thedisease can be transmitted from person to person.Legionnaires’ disease develops within 2 to 10 days afterexposure to L. pneumophila. Symptoms of legionnaires’disease may include loss of energy, headache, nausea, highfever, and muscular pain, followed by a dry cough andpneumonia. About 50% of patients become confused ordelirious and about 30% also develop diarrhoea orvomiting. The symptoms can be indistinguishable frompneumonia and it is possible that many L. pneumophilainfections are misdiagnosed as viral pneumonia, ratherthan the bacterial legionnaires’ disease.Pontiac fever develops within five hours to three days afterexposure, exhibiting influenza-like symptoms. Victimsgenerally recover in two to five days without treatmentLegionnaires’ disease has a reported 1% contraction ratefor exposed persons. The infection risk increases with theconcentration of legionella in the air, the respiratory rateof the individual, the length of time the person is exposedand the ability of the individual to fight off the infection.Persons at a higher risk of infection include:• Males (who are three times more susceptible thanfemales).• Adults, particularly those over 50 years.• Those with pre-existing respiratory disease.• Smokers.• Alcoholics.• Those with immunosuppressive illnesses, e.g. cancer,diabetes, AIDS, or kidney disease.• Those undergoing immunosuppressive drug therapy,e.g. organ-transplant and chemotherapy patients.Microbiology of legionellaThe general requirements for growth of populations oflegionella are tepid stagnant water with a ready supply ofnutrients.• Growth can occur between 25 - 45°C, the optimumgrowth temperature being 36 - 37°C. Below 20°Clegionella is dormant (not killed), while temperaturesabove 60°C will kill the bacterium.• Potential nutrients include sludge, scale, rust,organic material (algae, leakage of jointing andsealing materials) or dirt.• The presence of microscopic organisms (protozoa)such as amoebae can greatly promote thereproduction of legionella as the bacteria canmultiply intracellularly.• The optimum pH for growth is between 5.0 and 8.5.• The presence of oxygen is essential as legionella arestrict aerobes.Direct sunlight may inhibit the multiplication of legionellabut can promote the growth of algae. The formation ofbiofilms is thought to play an important role in harbouringlegionella and providing favourable growth conditions. Abiofilm is a layer of micro-organisms contained in a matrix,which may form a slime on surfaces in contact with water.Incorporation of legionella in biofilms and enclosure withinprotozoa can protect the organisms from biocideconcentrations that would otherwise kill or inhibit legionellafreely suspended in water.LegislationThere are no named Regulations for protecting againstlegionellosis. An approved code of practise is published byHealth and Safety Commission 2 , detailing the generalduties of employers under the Health and Safety at WorkAct and Control of Substances Hazardous to HealthRegulations for hazardous micro-organisms. Guidance oncontrolling legionella is also published by Health andSafety Executive 3,4 . Legionnaires’ disease is not anotifiable infectious disease, although it comes under theReporting of Injuries, Diseases and Dangerous OccurrencesRegulations 1995 as a biological agent, so if your employeecontracts legionnaires’ disease, you have to report it.FIRE FIGHTING SYSTEMSFire fighting systems (FFSs) for a site may consist of acombination of:• Sprinklers - heat activated heads to control a firewithin a building,• Drenchers - open sprinkler heads for complete waterdrenching of internal and external areas, or• Site fire-fighting ring mains - hydrants around thesite to which hoses may be attached.These have connecting pipework and an appropriatewater supply. The water supply may be either direct fromthe public water mains or from a private tank. The FFSmay also have an automatic pump to aid the distributionof water. Other FFSs such as portable water fireextinguishers are not considered a risk.Private tanks may be: a gravity tank, an elevated reservoiror a pressure tank (containing the water under pressure). A2

gravity tank or elevated reservoir may be fed from eitherthe mains or another private source (e.g. local river orpond). Example tank materials include concrete, glassfibre-reinforced plastic, galvanised and ungalvanised steel,and butyl rubber lined aluminium. Tanks fed from themains are required to be cleaned and maintained every 15years, otherwise tank maintenance is required every 3 years.The installations (sprinklers, drenchers and ring mains) andpipework are generally constructed of steel, but can be of anyappropriate material. Usually, the whole FFS is constantlycharged with water. Cleaning of the pipework only occurs if alarge amount of corrosion is found in the storage tank or ifsolid accumulation in pipework is suspected for other reasons.ASSESSMENT OF RISKFor human infection to occur, any legionella present in aFFS would have to grow to an infectious level, be presentin an aerosol and be inhaled by a susceptible individual.These stages are assessed below.Potential for bacterial growthIt should be accepted that some legionella will probably bepresent in all water systems, including supplied mainswater. The question is whether conditions in a FFS wouldsupport the continued existence and growth ofpopulations of legionella. As mentioned above, the generalgrowth requirements for legionella are stagnant, tepid andoxygenated water, with a ready supply of nutrients (SeeTable 1). The concentration of legionella regarded asinfectious is hard to define, as the infectious dose willdepend largely on the method of delivery.Overall the temperature within FFSs will be below, orclose to, ambient at which legionella bacteria would bedormant. However, some pipework may become warmer,as might external/roof top tanks or tanks in roof voids.Water is stagnant in virtually all FFSs, potentiallyallowing an internal build up of biofilm. However, this isonly likely in areas exposed to light, of which there shouldbe none 1 . Some agitation of the water in storage tanks islikely during the weekly pump flow testing.Nutrients, in the form of rust and scale, will be presentthroughout the FFS. No organic material should bepresent in the FFS.Generally the conditions within FFSs are not thought tobe able to support growth of legionella, but there is apossibility that a poorly maintained private tank,allowing organic material and warmth to enter, mightoffer conditions for legionella to multiply.Potential for legionella transmissionThe potential for droplet formation and dispersal canoccur:• During installation/due to faulty plumbing• During maintenance/cleaning of pumps (weekly) /tanks (every 3 or 15 years)• During accidental sprinkler release (very rare) orsprinkler operation.The droplet size created will be generally of the order of0.5 mm, compared to the 5 µm (some 100 times smaller)needed to pass into the alveoli. However, smaller dropletscan be formed from larger ones evaporating or breakingup, resulting in a potentially inhalable fraction.The risk of being infected during operation is very low: thetriggering conditions for a sprinkler would tend to precludeany unprotected person being in the operational area.Potential for human infectionThe people most likely to be exposed are fire-fightingprofessionals and FFS maintenance personnel. Thepotentially exposed people who are most likely to become illare those in health care premises and people with existinglung disease.CONTROL OF LEGIONELLAManagement systemIncorporate FFSs (especially storage tanks) into anyexisting site legionella monitoring system.Table 1: Comparison of conditions in fire fighting systems and those required for growth of legionella.Component Bacteria Pipework & Water supplygrowth installationsrequirementsProperty Public Elevated private Gravity Automatic Pressuremains reservoir tank pump tankTemperature range 25 - 45 °C Ambient Ambient Ambient Ambient Ambient AmbientStagnant water † † ✜ † † † †Contamination- Organic † ✜ ✜ ? ✜ * ✜ ✜- Iron † † † † † † †Oxygen † ✜ ‡ † † ✞ ✞ ✞Light † ✜ ✜ ? ✜* ✜ ✜Bacterial growth - ✜ ✜ ? ✜ ✜ ✜† - Condition present. ✜ - Condition not present. ? - Condition possible. * See ref. [1]. ‡ Deoxygenated due to rust formation.3

Water sampling and treatmentRoutine water sampling for legionella has generally not beenrecommended as a method of determining risk, due to thelarger importance of the other risk factors discussed above,i.e. the formation and inhalation of aerosols 3 .However, it may be prudent to monitor the water qualityon a regular basis (e.g. yearly) using a simple quickbacterial assay such as a dip slide (measures total bacterialconcentration, not just legionella 4 ). Dip slide results withcolony forming units per millilitre counts above 100,000(10 5 cfu/ml) indicate that some remedial action isnecessary. To ensure any remedial action is successful,subsequent testing (and any further action required)should be performed at more frequent intervals untilbacterial concentration is below 100,000 colony formingunits per millilitre.The preferred method of chemical water treatment forcontrol of legionella (or any bacteria) is the use of abiocide such as chlorine dioxide. One of the difficultiesassociated with biocides is the lack of biofilm penetrationand it may be necessary to incorporate a dispersant toassist in the disinfection. The possible effect of chlorinelevels on the variety of building materials used in privatetanks (e.g. bitumen-lined concrete, steel and plastics)should be considered. It is recommended that any suchchemical water treatment is performed by a watertesting/treatment consultant.Other control methodsTo help prevent the growth of legionella, the FFS tankand piping should be kept cool (< 20°C), i.e. away fromany sources of heat such as sunlight, nearby hot waterpipes, heating ducts or warm air currents.To prevent the build-up of nutrients, visual inspection ofstorage tank condition, including monitoring for rustand internal deposits (e.g. sludge, biofilm), should beperformed annually. Internal deposits or any tankdeterioration should be corrected.During testing and maintenance of the FFS, proceduresshould minimise the production of aerosols and theexposure to persons nearby.CONCLUSIONS• FFSs directly supplied with public mains water presentno significant risk of infection with legionella.• FFSs supplied with water from poorly maintainedprivate tanks present a theoretical risk of infectionwith legionella, particularly to maintenancepersonnel, fire-fighting professionals and in healthcare premises.• LPC recommended control measures:• Incorporate FFS into any existing legionellamonitoring system for the site.• Minimise production of aerosols during testingand maintenance.• Maintain tanks and piping at < 20°C byshielding from possible heat sources.• Annual inspection of tanks to monitor corrosionand deposit build-up, with appropriate remedialactions.• Annual monitoring of water tank bacterialconcentration by dip slide. Concentrationsabove 10 5 cfu/ml indicate that chemicaltreatment of the water may be necessary.REFERENCES1 BS 5306(2) clause 17.3.1.3 - "the tank shall becovered to exclude daylight and solid matter"2 The control of legionellosis (including legionnaires’disease). ACoP, HSC, London. 19953 The control of legionellosis including legionnaires’disease. HS(G)70, HSE, London. 19934 HS(G)70, paragraphs 122-5.5 The control of legionellosis in hot and cold watersystems. HS(G)70 supplement, HSE, London. 1998FURTHER INFORMATIONMinimising the risk of legionnaires’ disease. TechnicalMemorandum 13, CIBSE, London, 1991Legionellosis. The New England Journal of Medicine,337 (1997), 682-7.BS 6068-4.12: 1998 Water quality. Microbiologicalmethods. Detection and enumeration of legionella.BS 7592: 1992 Methods for sampling for legionellaorganisms in water and related materials.Water testing/treatment consultants can be found inyellow pagesLPCFor further information please contact:Dr Richard Bailey, LPC Centre for Risk Sciences, BRE, Garston, Watford, WD2 7JRTelephone: 01923 664000 E-mail: frsenquiries@bre.co.ukWeb: www.bre.co.uk4