Legionella in Offices: 8 Things Occupancy Changed
Legionella is usually associated with cooling towers, spa pools and large industrial water systems. Office occupiers reasonably assume it is somebody else's problem.
That assumption has aged badly. The control that matters most in an ordinary building is water movement, and the last few years have changed water movement in almost every office in the country. Floors sit empty two days a week, desks are unoccupied, meeting room kitchenettes go unused, and end-of-trip showers are used by a handful of people.
The risk did not arrive with new equipment. It arrived with lower occupancy.
Eight things.
1. The duty applies to ordinary buildings
There is no legionella-specific regulation. The duty arises from general law.
Section 3 of the Health and Safety at Work etc. Act 1974 requires employers to conduct their undertaking so that people not in their employment are not exposed to risk, and regulation 6 of the Control of Substances Hazardous to Health Regulations 2002 requires assessment of risks from substances hazardous to health, which includes biological agents.
HSE's approved code of practice L8 sets out the control of legionella bacteria in water systems, and its legionnaires' disease pages cover the practical arrangements.
The duty is to assess and control. It applies to a normal office water system, not only to industrial plant.
2. The risk in an office is not where people look
Three conditions have to coincide: water at a temperature that lets the bacteria multiply, something for it to feed on, and a means of creating breathable droplets.
In an office that points to a short list, and it is not the cooling tower most people picture.
Infrequently used outlets, where water sits. Showers, which produce exactly the aerosol required. Hot and cold water storage at the wrong temperature. Dead legs, meaning pipework left in place after a fit-out and no longer serving anything. And occasionally spray taps, water features and humidifiers.
Drinking water coolers and kettles are not the issue. Showers and stagnant pipework are.
3. Infrequently used outlets are the central problem now
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The direct consequence of the occupancy change, and the one most buildings have not adjusted for.
An outlet that was used forty times a day in 2019 may now be used twice. A floor that was fully occupied may be half let or sublet. A kitchenette serving a team that now attends on Tuesdays and Wednesdays sits unused for five days at a time.
The established control is regular flushing of outlets that are not in regular use, typically weekly, running them long enough to replace the water in the pipework.
Two practical points. Somebody has to own the flushing schedule, and it is usually either not assigned or assigned to a cleaning contract that does not mention it. And the schedule has to reflect current usage, which means revisiting it whenever occupancy patterns change rather than keeping the one written at fit-out.
4. Showers deserve particular attention
The highest-risk item in a typical office building.
End-of-trip facilities, cycle storage showers and gym facilities all produce fine aerosol, and they are frequently used by a small number of people, which is the worst combination: aerosol generation plus low throughput.
The usual controls are regular use or flushing, cleaning and descaling of shower heads and hoses at defined intervals, and attention to temperature. Where a shower is genuinely out of use, the better answer is often to take it out of service properly rather than leave it idle.
5. Temperature control is the other half
Alongside movement sits temperature, and the parameters are well established.
The principle is to keep hot water hot and cold water cold, so that bacteria cannot multiply. In practice that means hot water stored and distributed hot enough to control growth, cold water kept below the temperature at which growth accelerates, and both reaching outlets at the right temperature within a short run.
This is where the tension covered elsewhere in this series appears: water hot enough for legionella control is hot enough to scald, and the resolution is thermostatic mixing at the outlet rather than reducing storage temperature. Lowering the stored temperature to prevent scalding creates a legionella risk.
Monitoring temperatures at sentinel outlets is part of any control scheme, and it is one of the records an insurer or auditor will ask to see.
6. Dead legs and fit-out legacy
The hidden one, and offices accumulate it.
Every fit-out, reconfiguration and tenancy change leaves pipework behind. A kitchen removed, a tea point relocated, a shower decommissioned at the valve rather than at the main. Each leaves a section of pipe holding water that never moves.
These do not appear in a usage schedule because nobody uses them, and they do not appear in a drawing because the drawing was not updated. A risk assessment that has not looked for them has not looked at the main structural risk in an altered building.
7. The landlord and tenant split, which is rarely written down
The question that decides whether any of this is yours.
In a typical leased office, the landlord holds responsibility for the incoming supply, storage and the system serving common parts. The tenant typically holds responsibility for outlets and pipework within its demise, and certainly for anything it installed during fit-out.
Three practical steps. Read the lease rather than assuming. Ask the landlord for their risk assessment and control scheme covering the parts they hold, and check what areas it actually covers. And treat anything you fitted as yours, including the kitchenette and the shower in your end-of-trip facility.
The common failure is both parties assuming the other holds the outlets.
8. The control scheme and the records
What good looks like, and it is not a long document.
A written risk assessment identifying the systems, the risks and who is responsible. A written control scheme setting out what is done, by whom and how often: flushing, temperature monitoring, cleaning and descaling, tank inspection. A named responsible person. Records of monitoring and actions, kept and reviewed. And review triggers, which for current purposes means any change in occupancy, any alteration to the system, and any period where part of the building has been out of use.
That last trigger is the one to act on now. Any building whose occupancy has materially changed since its assessment was written needs that assessment revisited.
The eight, in short
| Point | Position |
|---|---|
| The duty | General law: section 3 and COSHH, with L8 as guidance |
| Where the risk is | Infrequently used outlets, showers, storage, dead legs |
| Occupancy change | Flushing schedules written for a fuller building |
| Showers | Aerosol plus low throughput; the highest-risk item |
| Temperature | Hot hot, cold cold, mixed at the outlet |
| Dead legs | Fit-out legacy nobody uses or records |
| Landlord and tenant | Follows the lease; fit-out items are yours |
| The scheme | Assessment, scheme, named person, records, review triggers |
Rows three and six are where the actual risk sits in most offices today, and neither is visible without somebody deliberately looking.
What to do this month
Four steps, none of them expensive.
Find your risk assessment and check its date. If it predates your current occupancy pattern, it describes a different building.
Ask who flushes, and look at the record. The answer "the cleaners, probably" is the one to worry about.
Walk the building for outlets nobody uses. Kitchenettes on quiet floors, showers, taps in meeting room areas, and anything in a space that has been sublet or vacated.
Ask the landlord for their documentation, and establish in writing which parts they cover.
Periodic health and safety audits frequently find control schemes that have never been updated for how the building is now used, and holding the scheme, the monitoring records and the review dates in one register is where health and safety consultants and software are worth more together than either alone.
For international groups
Two considerations.
Requirements are national and some are more prescriptive. Several jurisdictions covered in this series set specific water hygiene duties, testing regimes and reporting requirements with no direct British equivalent, and in some the responsible person must hold a prescribed qualification.
Climate changes the analysis. Cold water in warmer countries sits closer to the temperature range in which bacteria multiply, which makes cold side control a bigger issue than it is in Britain.
Our global health and safety consultants establish what each jurisdiction requires, and our international health and safety consultants keep that current.
Where Arinite fits
Arinite's legionella work covers the assessment, the control scheme and the practical question of who holds what under the lease, which in a multi-tenant building is usually undocumented. We support 1,500+ businesses across 50+ countries and protect 100,000+ employees, with 95%+ client retention over 15+ years.
Our health and safety consultants work extensively with legal, insurance, education and IT and software organisations, most of which occupy buildings they do not own and have changed how they use them.
If part of your building has been lightly used for a while and nobody has revisited the flushing schedule, a free gap analysis is the right place to start.
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Arinite Health & Safety Consultants
Health & Safety Expert at Arinite
