Legionella Myths: Why It Doesn't Come From Your Air Conditioning Vents

What usually goes wrong, why it happens, and what a thorough audit looks for

When we audit the fire safety side of a building's mechanical services, we rarely find deliberate corner-cutting. More often, we find an installer who didn't fully understand the standard they were working to. The work looks finished; it may even be signed off, but a missed detail can matter a great deal when there's an actual fire.

Those details are easy to overlook because most fire safety systems sit idle for years. A smoke exhaust fan or a stair pressurisation system might only run during testing. So the only real chance to find a problem is a proper inspection by someone who knows what to look for.

Here are the issues we come across most often, and why each one matters.

Mistake 1: Standard Cabling on Life-Safety Equipment

Some systems are designed to keep running during a fire. Smoke exhaust fans are the obvious example. Their job is to pull smoke out of a space such as a shopping centre or car park so people can get out and firefighters can get in.

If the power cable feeding that fan is ordinary cable, the fire can burn through it, and the fan stops. That's the moment it's needed most. Equipment like this needs fire-rated cabling, built to keep working for a set period at extreme temperatures.

From the outside, a fire-rated cable and a standard cable can look similar, and the fan runs perfectly well on either during a routine test. That's why this one so often goes unnoticed until someone traces the cabling back and checks what was actually installed.

Mistake 2: Fan Capacity Not Reassessed After the Building Changed

A building's mechanical design is based on how it was drawn. Plans change during construction and over a building's life. Floors get added, tenancies get reconfigured, and occupancy goes up.

A good example is a stair pressurisation system. If a stairwell was designed for a certain number of levels and a couple more are added later, the fan that pressurises it may no longer be big enough. Nobody necessarily went back to check, because the fan still turns on and still moves air. It just doesn't move enough to keep smoke out of the stairs across the full height of the building.

We see the same pattern with car park and smoke exhaust systems. The equipment is fine. It's simply been asked to do more than it was sized for.

Mistake 3: Penetrations Too Close to Fire Dampers

On a busy construction site, many trades are competing for the same ceiling and wall space. Plumbers, electricians and data installers all need to get through walls, and fire dampers sit inside those same walls.

A pipe or cable tray installed too close to a damper can affect its performance or prevent it from closing properly. It can also happen years after handover, when a new fit-out puts a penetration somewhere it shouldn't be. This is one reason scheduled damper inspections are worth doing properly. Our post on fire damper testing explains how that inspection cycle works.

Mistake 4: The System Doesn't Behave the Way the Fire Strategy Intends

In a fire, a building's fans are meant to respond in a set sequence. Some start to exhaust smoke, others stop, and others pressurise stairs or corridors. The building's fire engineering documentation sets out that sequence.

When we test a building, we sometimes find that the sequence doesn't match what the fire strategy actually needs, even where it matches the paperwork. When that happens, we raise it with the fire engineer so we can bring the documentation and the system back in line.

Why These Issues Happen

Most of these problems come down to knowledge, not intent. Fire safety standards are detailed and they change over time. A tradesperson who mainly does general mechanical work may not encounter these requirements often enough to know them inside and out.

That's also why we think an audit should be constructive. The goal is to find genuine risk and fix it, not to blame whoever installed the system.

Why This Work Is Taken So Seriously

The 2017 Grenfell Tower fire in London, which claimed 72 lives, is the best-known recent example of how a building compliance failure can have devastating consequences. That fire involved external cladding, not mechanical services. It still changed how seriously building compliance is treated, including in Australia, where buildings across the country were audited for combustible cladding in the years that followed.

The lesson for building owners is simple. Fire safety systems are only as good as the detail in their installation and upkeep.

What a Thorough Audit Actually Looks For

A proper audit goes beyond switching equipment on and checking that it runs. On our audits, we check:

•  Cabling on life-safety equipment, and whether it's rated for fire conditions.

•  Fan capacity against the building as it stands today, not as it was originally drawn.

•  Clearances and penetrations around fire dampers.

•  Airflows and pressures in stairwells and exhaust zones, measured rather than assumed.

•  Whether the system's fire mode sequence matches the fire engineering strategy.

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Afterwards, we sit down with the building owner, go through what we found, and explain which items need attention first. Where a finding is borderline, a fire engineer may be able to assess it through a performance solution rather than full rectification.

If you'd like a second set of eyes on your building's fire safety systems, talk to the team.

Talk to the team about your Mechanical Fire Safety needs.

Where Legionella really comes from, who is most at risk, and why cooling towers are so closely regulated

One of the questions we hear most often is some version of this: can I catch Legionella from my air conditioning? It's an understandable worry, especially after a news story about an outbreak. The short answer is no. Legionella doesn't come out of the vents and grilles in your office, shop or home.

The bacteria linked to most large outbreaks come from cooling towers, a specific piece of plant used on larger commercial buildings. Knowing the difference helps building owners focus on the right risk.

Where Legionella Actually Comes From

Legionella bacteria live naturally in water. They become a problem when they're given the right conditions to multiply, such as warm, still water, sludge and biofilm, and poor water treatment.

A cooling tower can provide exactly those conditions if it isn't looked after. Cooling towers work by evaporating water to reject heat from a building's air conditioning. That process involves warm water and moving air, and it releases fine water droplets into the air around the tower.

Most split systems, ducted residential units, and car air conditioners don't use a cooling tower. They use air to reject heat, not open evaporating water. The air coming out of their vents isn't the source of Legionella, as many people imagine.

How It Actually Spreads

People get Legionnaires' disease by breathing in fine droplets of contaminated water. With a cooling tower, those droplets are released from the top and can be carried by the wind.

That means people most likely to be exposed are often outside the building, nearby or downwind, rather than people inside. It also explains why outbreaks are usually investigated by mapping where affected people had been, then tracing back to towers in that area.

According to NSW Health, Legionnaires' disease is not normally spread from person to person.

Who Is Most at Risk

Most healthy people who come into contact with Legionella won't become seriously unwell. Some may have mild, flu-like symptoms.

The risk is much higher for some groups. NSW Health notes that middle-aged and older adults are most affected, particularly smokers and people with chronic lung disease, along with people whose immune systems are weakened by illness or medication. For them, Legionnaires' disease can cause serious pneumonia.

This is one reason cooling tower management matters so much near hospitals, aged care facilities and other places where vulnerable people live, work or visit.

Why Cooling Towers Are So Heavily Regulated

Because a poorly managed tower can affect people well beyond the building it serves, NSW closely regulates cooling towers. Owners must register each tower with council, have a risk management plan in place, test the water monthly, and have the system independently audited annually.

These rules exist because the risk is real but manageable. When a tower is properly treated, cleaned and tested, the risk of it becoming a source of Legionella is much lower. We cover what happens at each stage of that schedule in our post on monthly, quarterly and annual cooling tower servicing.

What Building Owners Can Do

If your building has a cooling tower, the most useful steps are practical ones:

•  Make sure the tower is registered and has a current risk management plan.

•  Check that monthly testing is happening and that results are being recorded.

•  Ask your contractor to tell you early if results are trending upwards, rather than waiting for a failed test.

•  Keep records organised for the annual audit.

If you don't have a cooling tower, the air conditioning in your building isn't a Legionella source in the way many people fear. Regular servicing still matters for comfort, efficiency and indoor air quality, which are separate issues.

Common Questions

Can I get Legionella from a split system air conditioner?

Split systems don't use open evaporating water the way cooling towers do, so they aren't the kind of system usually linked to Legionnaires' outbreaks.

Are the people inside a building with a cooling tower at risk?

The main exposure risk comes from droplets released from the tower and carried on the wind, so people nearby and downwind are usually the focus. A well-located and well-maintained tower keeps that risk low for everyone.

How often are cooling towers tested in NSW?

Cooling water must be sampled and tested monthly, and each system must be independently audited annually.

What happens if a test comes back high?

The owner must notify council within 24 hours, and the system is treated and retested until results are back within safe limits.

How We Approach It

We manage cooling towers on a planned schedule, with monthly testing, regular cleaning and clear records ready for the annual audit. We also explain results in plain terms, so building owners and facility managers know where they stand and what, if anything, needs to happen next.

If you have questions about your cooling tower, or you're not sure whether your building has one, talk to the team.

Talk to the team about your Chillers & Cooling Towers needs.

A plain-language guide to the cooling tower maintenance year in NSW

If your building has a cooling tower, you're probably paying for a maintenance contract with visits spread across the year. It isn't always clear what happens at each visit, or why some take an hour while others take most of a day.

The short answer is that cooling tower maintenance runs on a yearly schedule. Different work happens at different points in the year, and much of it is tied directly to NSW law. Here's how that schedule usually breaks down.

Why Cooling Towers Are Treated Differently

A cooling tower rejects heat from a building's air conditioning by evaporating water. Warm water, air and sunlight are good conditions for bacteria, including Legionella. If a tower isn't managed properly, that bacteria can grow and be carried away from the building in fine water droplets.

That's why cooling towers in NSW are regulated under the Public Health Regulation 2022, and why so much of the work involves testing and record-keeping, as well as mechanical repairs.

Every Month: Testing and Early Checks

Monthly visits are the backbone of the schedule. NSW requires monthly cooling water sampling and testing for Legionella and heterotrophic colony count, a general measure of bacteria in the water.

On a typical monthly visit, we also:

•  Check water treatment levels and dosing equipment.

•  Look for corrosion, scale, sludge or biofilm building up.

•  Check that fans, pumps and drift eliminators are working as they should.

•  Record what we found so it's ready for the next audit.

If a lab result comes back above the levels set in the regulation, the owner has to notify council within 24 hours, and the system needs to be treated and retested. Catching a rising trend early through regular monthly checks is the best way to avoid reaching that point.

Every Quarter: Deeper Cleaning

Quarterly visits are longer and more hands-on. Depending on the tower and its risk management plan, this is when the tower may be drained down, cleaned out and pressure washed to remove sludge and biofilm that chemical treatment alone won't shift.

Because the tower has to come offline for part of this, we plan these visits with the building manager to keep the impact on cooling to a minimum.

Every Year: The Independent Audit

Each year, an independent auditor must check the cooling water system against its risk management plan and the regulation. The auditor reviews the tower itself and the paperwork: test results, maintenance logs, and any corrective actions taken during the year.

There are a few other annual and ongoing obligations to keep track of:

•  Every cooling tower must be registered with the local council.

•  The tower must display a unique identification number issued by the council.

•  A risk management plan must be in place and reviewed at least every five years, or sooner if something changes.

•  Certificates for the risk management plan and the annual audit must be sent to council within seven days of completion.

NSW Health has more detail on the independent audit requirements.

Why the Records Matter as Much as the Work

Almost everything about cooling tower compliance comes back to proving it. When the auditor or council asks, you need to produce test results, service records and certificates for the whole year. Saying the work has been done isn't enough.

We've seen buildings where the tower itself was in reasonable shape, but the records had gaps. That's a compliance problem in its own right, and it's an easy one to avoid if records are kept as the work happens.

Is a Cooling Tower Still the Right Choice?

For some buildings, it's worth asking whether a cooling tower is still the best option. Alternative heat rejection systems now exist that don't rely on open evaporative cooling. These generally need less testing, less chemical treatment and less ongoing maintenance, which can also help with insurance.

Each option has trade-offs in cost, efficiency, and space, so it's a decision best made with good advice. When a tower is due for major work or replacement, it's a good time to have that conversation.

How We Approach It

We service cooling towers on a planned yearly schedule, with each visit aligned with regulations and your risk management plan. We keep the records organised so the annual audit isn't a scramble, and we tell you early if test results are trending the wrong way.

Where it helps, we also connect cooling tower performance with the rest of the plant, including your chillers and building management system, so we catch problems across the whole system.

If you'd like to review your current cooling tower program, talk to the team.

Talk to the team about your Chillers & Cooling Towers needs.