Data center nuisances

Q: How far away from a data center is considered safe?

There is no regulated distance between a data center and homes. What the rules govern is not separation but emergence : how much the noise rises at the neighbour's when the plant runs. The French order of 23 January 1997 generally allows +5 dB(A) by day and +3 dB(A) at night . The consequence runs against intuition: the same machine does not have the same effect everywhere . Countryside that drops to 30 dB(A) at night leaves almost no headroom, while an industrial district absorbs it. Two houses the same distance from two identical sites do not live the same life. That is why we publish the distance to the nearest dwellings on each fiche where we have it: it is the one parameter nobody can fix afterwards, and it should be read alongside the rest of the file. Find the site near you on the map .

Q: Are there health risks to living near a data center?

We are not a health authority and we measure no health effect — asserting one, or denying it, would be equally dishonest. What we can say rests on the facts filed in the dossiers. What comes up most often in the environmental-authority opinions we reviewed: backup generators , fuel tanks and noise . Night-time noise is the most constant subject, because it is continuous and has no lull — that is what sets a data center apart from a building site or a road. We publish these facts next to the grade, never inside it , and we say what they rest on. To see when these questions can still change a project, read Rights and calendar (in French).

A data center is usually argued over its global balance sheet — electricity, climate. What is experienced from the street is more concrete: continuous noise, backup generators under test, fuel tanks, water abstracted and discharged. Across the 41 French environmental authority opinions we reviewed, backup generators come up most often, ahead of fuel tanks and noise.

Noise, the everyday nuisance

A data center never stops: it continuously evacuates the heat of its machines. The noise therefore comes not from the building but from what sits on and around it — fans, dry coolers, chillers — and it is continuous, day and night. That is what sets it apart from a building site or a road: there is no lull.

Three things matter more than the raw level:

The gap with background noise, not the absolute decibel. French regulation for classified installations reasons in terms of “emergence”: the order of 23 January 1997 generally allows +5 dB(A) by day and +3 dB(A) at night at the neighbour's, with a site-boundary ceiling of around 70 dB(A) by day and 60 dB(A) at night. The direct consequence: countryside that drops to 30 dB(A) at night leaves almost no headroom, while the same machine disappears into an industrial district. The same equipment is not acceptable everywhere.
The distance to the nearest dwellings. It is the one parameter nobody can fix afterwards, which is why we measure it site by site.
Tonality. A whine or a hum on a marked frequency is noticed far more than a diffuse rush at the same level; regulation treats it separately for that reason.

Cooling technology changes the picture: an air-cooled site relies on large fan banks that speed up precisely during heatwaves — when windows are open. An adiabatic or water-cooled site blows less hard, but consumes water. Liquid cooling at the chip reduces fans further. There is no choice without a trade-off: noise, water and electricity are exchanged against one another.

Backup generators: why they count as a nuisance

These engines produce nothing in normal operation. They exist so the site survives a grid outage — and a data center sizes its fleet to carry its entire load, cooling included, with redundancy on top. As an order of magnitude, a site of several tens of megawatts therefore lines up several dozen engines the size of a ship's. It is a backup power station, parked at the edge of town.

Neighbours do not hear them during outages, which are rare. They hear them during the periodic tests that are required to guarantee the engines will start: typically one test per month per machine, plus a longer load test once a year. A site with thirty engines therefore runs tests very regularly, and that is by far the first source of friction in the files we read.

From what point is it “a lot”? Two markers rather than a figure: the fleet's aggregate power — beyond a certain thermal threshold it moves the installation into a more demanding authorisation regime for classified installations — and the ratio between that power and the size of the municipality. It is the second ratio that explains why the same project passes unnoticed in an industrial zone and stalls elsewhere.

Fuel tanks: quantity before substance

Generators mean reserves: the engines must run for hours, sometimes days, without a delivery. A file therefore declares a storage volume, and that volume is what we record.

The declared fuel varies: some opinions declare hydrotreated vegetable oil, others heating oil or diesel.

So what? The substance matters less than three things:

The quantity stored. That is what measures the risk: a few cubic metres and several hundred are not managed the same way, and it is volume thresholds — not the nature of the product — that trigger the heaviest obligations.
Containment. Double-skinned tanks, retention bunds able to hold both the fuel and the water used to fight a fire: that is where most of it is decided. An uncontained spill near a drinking-water catchment or a watercourse is the scenario that worries the authorities.
What comes out of the exhaust during tests. Nitrogen oxides and particulates, at roof height, during working hours.

So what is virtuous? Less volume, better contained, and a cleaner fuel. Hydrotreated vegetable oil clearly reduces emissions and is not fossil — but it burns, and it is stored in the same tanks: it improves the balance, it does not remove the risk.

Water: the volume, but also the discharge

Cooling with water costs far less electricity than cooling with air — the same trade-off as above, seen from the other side. Two questions follow: how much is abstracted, and from which resource. A modest volume taken from a catchment already stressed in summer weighs more than a large volume taken elsewhere.

Discharge is the forgotten half: the water leaves warmer, more concentrated in salts, and treated against scaling and legionella. For a municipality the question is not only “how much”, but “to where, at what temperature, with what treatment”.

Electricity: the nuisance you cannot see

It is neither heard nor smelt, yet it often decides. A high-power connection consumes grid capacity that the territory's other uses — industry, housing, transport — will not have for years, and its queue is counted in years. It is also what makes the generator fleet so large: the more powerful the site, the more imposing its backup.

The “hidden” part

An operator presents itself through its energy efficiency. It rarely highlights its generators, its tanks or the acoustic modelling the environmental authority requires of it. The gap between a communication brochure and the content of an assessment file is, in itself, information — and it is the raw material of this page.

When the site itself carries a hazard

Some projects store fuel in quantity on site, lithium-ion batteries, sometimes hydrogen. The site then carries a hazard instead of merely enduring one — that is no longer a nuisance but a risk, handled in the hazard study. We publish these elements as information, next to the grade, for as long as coverage does not allow grading them without distorting comparison between sites.

Where our measurement stands

Our corpus holds 3,267 sites. A distance to the nearest dwellings is available for 784 of them — the one exposure indicator we compute ourselves, the same way everywhere. The nuisance detail comes from the 41 environmental opinions reviewed: projects that went through assessment, not the whole estate. These facts are published next to the grade, not inside it.

See data center acceptability, the map and the method.

The questions people ask us

How far away from a data center is considered safe?

There is no regulated distance between a data center and homes. What the rules govern is not separation but emergence: how much the noise rises at the neighbour's when the plant runs. The French order of 23 January 1997 generally allows +5 dB(A) by day and +3 dB(A) at night.

The consequence runs against intuition: the same machine does not have the same effect everywhere. Countryside that drops to 30 dB(A) at night leaves almost no headroom, while an industrial district absorbs it. Two houses the same distance from two identical sites do not live the same life.

That is why we publish the distance to the nearest dwellings on each fiche where we have it: it is the one parameter nobody can fix afterwards, and it should be read alongside the rest of the file. Find the site near you on the map.

Are there health risks to living near a data center?

We are not a health authority and we measure no health effect — asserting one, or denying it, would be equally dishonest. What we can say rests on the facts filed in the dossiers.

What comes up most often in the environmental-authority opinions we reviewed: backup generators, fuel tanks and noise. Night-time noise is the most constant subject, because it is continuous and has no lull — that is what sets a data center apart from a building site or a road.

We publish these facts next to the grade, never inside it, and we say what they rest on. To see when these questions can still change a project, read Rights and calendar (in French).

More — what is an environmental authority opinion worth?

For projects of this size the developer must produce an impact assessment. A body separate from the service that will grant the permit examines it and issues a public opinion: in France, the environmental authority, most often a regional mission (MRAe).

What that opinion is: an expert view on the quality of the file and on how the project accounts for the environment, with recommendations. What it is not: an authorisation, nor a refusal. The opinion does not decide the project.

It is not decorative either. The developer must answer it in writing, and both opinion and answer are attached to the file put to public consultation; the permitting authority must justify its decision in their light. In practice an opinion that points to a gap forces the file to be completed, and gives elected officials and residents something solid to stand on. It is the single most useful document to read before forming a view on a project — and it is our raw material.

More — how a project's noise is assessed

Before construction, an acoustician measures the existing background noise, by day and by night, at the nearest dwellings. The site in operation is then modelled and compared: what is judged is the gap between the two, not the machine's own level. Commitments follow — screens, enclosures, fans slowed at night, generator tests barred in the evening — and a verification campaign after commissioning is normally required.

Two classic weaknesses, visible when reading the opinions: background noise measured out of season or on a poorly chosen day, which inflates the available headroom; and modelling done at nominal fan power when the real peaks arrive in a heatwave. Hence the value of post-commissioning measurements — and of distance to dwellings, which at least cannot be renegotiated.