When we show a client a value measured on their property, say 40 nT of low-frequency magnetic field, the question that almost always follows is: "is that good or bad?". The honest answer is: it depends which reference you're comparing it to. That is exactly where the most common confusion in the field of electromagnetic fields (EMF) arises: the generic term "standard" gets used for documents that have neither the same legal status, nor the same purpose, nor the same level of scientific evidence.
This article sets out to clarify three families of references (legal limits, precautionary values, and building-biology grids), then to explain two principles that are often quoted but rarely defined correctly: the precautionary principle and the ALARA principle.
Three families of values, three different statuses
Before comparing numbers, one technical distinction matters, because it explains why an EMF audit always presents two separate sets of tables:
- Low frequency (LF): fields tied to the electrical grid (50/60 Hz) and household electricity. Here we distinguish the electric field (measured in V/m) from the magnetic field (measured in nT, sometimes in mG, 1 mG = 100 nT).
- High frequencies / radiofrequencies (RF): waves emitted by Wi-Fi, mobile telephony (2G to 5G), DECT, mobile masts. Here we measure electric field strength (V/m), converted into power density (µW/m²), the unit most used to compare limits.
These are two distinct physical phenomena, with different units and orders of magnitude: an LF value is never compared to an RF value. For each of these two categories, the same three-tier hierarchy of references applies, detailed below.
1. Legal limits (binding)
These are the only values that carry legal force. In Europe, they build on the recommendations of ICNIRP (International Commission on Non-Ionizing Radiation Protection), taken up by European recommendation 1999/519/EC and then transposed into Belgian law through CENELEC (following ICNIRP 1998/EU). They set thresholds beyond which acute, well-established biological effects (tissue heating, nerve stimulation) can occur in the short term.
Low frequencies
| Quantity | ICNIRP / Belgian limit |
|---|---|
| LF electric field | 5,000 V/m |
| LF magnetic field | 200,000 nT (ICNIRP 2010) / 100,000 nT (Belgium, CENELEC) |
High frequencies / radiofrequencies
Here the limit is expressed as electric field strength (V/m) or as equivalent power density (µW/m²): the two columns below give the same limit in both units.
| Zone | Limit (V/m, eq. 900 MHz) | Limit (µW/m²) |
|---|---|---|
| Wallonia, indoors (since 2022) | 18.4 | 899,000 |
| Brussels, indoors | 9.19 | 224,300 |
| Brussels, outdoors | 14.57 | 563,500 |
| Flanders, indoors | 20.6 | 1,126,000 |
These values vary across Belgian regions, proof that the same physical quantity can be regulated differently depending on which level of government holds the power to do so. The table below situates these Belgian limits against the ICNIRP recommendation and a few neighbouring countries:
| Reference | Limit (V/m, eq. 900 MHz) | Limit (µW/m²) | Status |
|---|---|---|---|
| ICNIRP (2010) / WHO, base limit | 41.2 | 4,500,000 | International recommendation |
| France, public places (decree no. 2002-775) | 41 | 4,460,000 | Legally binding |
| Germany, public places | 41 | 4,460,000 | Legally binding |
| Switzerland, public places | 41 | 4,460,000 | Legally binding |
| Switzerland, sensitive-use places (homes, schools, permanent workplaces) | 4 | 42,400 | Legally binding |
| Italy, base limit | 20 | 1,060,000 | Legally binding |
| Italy, extended stays (> 4h/day) | 6 | 95,500 | Legally binding |
Among these countries, Switzerland and Italy are the only two that apply limits markedly stricter than the ICNIRP recommendation in sensitive-use or extended-stay places, and they do so as a matter of binding law rather than mere recommendation.
2. Precautionary values (recommended, not binding)
Below the legal limits, some authorities or bodies propose more cautious values, with no legal force but motivated by the precautionary principle (see below).
Low frequencies
| Reference | Quantity | Value |
|---|---|---|
| Brussels Region, precautionary value for children | LF magnetic field, 24h average | 4 mG (400 nT) |
| Sweden, Svenska kraftnät, voluntary internal policy | LF magnetic field | 4 mG (400 nT) |
| Sweden, TCO screens, 30 cm | LF electric field (ELF band) | ≤ 10 V/m |
| EUROPAEM (2016), daytime exposure | LF magnetic field (avg./max) | 1 mG / 10 mG |
| EUROPAEM (2016), sensitive populations | LF magnetic field (avg./max) | 0.3 mG / 3 mG |
High frequencies / radiofrequencies
| Reference | Context | Value (power density) |
|---|---|---|
| France, voluntary local charters (e.g. Paris) | Not binding, municipal initiative | 2 V/m, i.e. 10,600 µW/m² |
| EUROPAEM (2016) | Daytime exposure (Wi-Fi, 2G-4G) | 10-100 µW/m² |
| EUROPAEM (2016) | Sensitive populations (Wi-Fi, 2G-4G) | 0.1-1 µW/m² |
| BioInitiative | Target RF value (2007 → 2012) | 1,000 µW/m² → 3-6 µW/m² |
EUROPAEM (the European Academy for Environmental Medicine's EMF working group) brings together physicians and researchers in environmental medicine who work day to day with patients reporting electrohypersensitivity (EHS). Their recommendations translate that clinical experience into cautious thresholds, in a field where the scientific research on the long-term effects of non-ionising exposure remains active and still evolving. The BioInitiative Report follows the same logic: its 2012 revision lowered its target values (×10 compared with 2007) to account for effects reported across several studies (headaches, concentration and behavioural issues in children, sleep disturbances). Neither reference replaces ICNIRP's legal limits, but both give sensitive individuals and professionals a precautionary benchmark built from clinical observation.
3. Building-biology grids (Baubiologie / SBM-2024)
The Standard of Building Biology Testing Methods (SBM-2024), from the Institut für Baubiologie + Nachhaltigkeit (Germany), is yet another kind of tool: a comfort grid designed specifically for rest and sleep areas, on the basis that nighttime vulnerability warrants extra caution. It brings all three quantities together side by side: the only table in this article where low frequency and high frequency appear together, column by column.
| SBM-2024 category | LF, magnetic field | LF, electric field | RF, power density |
|---|---|---|---|
| No anomaly | < 20 nT | < 0.3 V/m | < 0.1 µW/m² |
| Slight anomaly | 20-100 nT | 0.3-1.5 V/m | 0.1-10 µW/m² |
| Severe anomaly | 100-500 nT | 1.5-10 V/m | 10-1,000 µW/m² |
| Extreme anomaly | > 500 nT | > 10 V/m | > 1,000 µW/m² |
SBM-2024 is a recognised professional methodology in the field of building biology, developed by a long-established German institute. It is a comfort target, designed for sleep areas and the vulnerability specific to them: it does not replace legal limits, but adds a finer level of stringency on top of them, particularly useful for sensitive individuals. For the magnetic field, the "extreme anomaly" threshold (> 500 nT) is still 200 times below the Belgian legal limit (100,000 nT); for radiofrequencies, the "extreme anomaly" threshold (> 1,000 µW/m²) is still more than 4,000 times below the ICNIRP limit at 900 MHz (4,500,000 µW/m²).
The takeaway: the further down this hierarchy you go (legal, precautionary, building biology), the tighter the thresholds get, offering a growing margin of protection for the most sensitive people. A measured value is never simply "good" or "bad" in absolute terms: it sits somewhere on several scales at once, and a serious audit report should show that explicitly rather than issuing an arbitrary verdict.
The precautionary principle
The precautionary principle is a principle of public action, enshrined notably in European law (the Treaty of Lisbon, Article 191 TFEU): when a risk is plausible but scientifically uncertain, it justifies proportionate cautionary measures, without waiting for complete scientific proof of harm. It does not claim a risk is proven: it says that in the face of reasonable doubt, it is legitimate to act with caution.
This is the principle underlying the Brussels precautionary value for children (4 mG, i.e. 400 nT): the authorities do not consider 5 or 10 mG to be dangerous (the legal limit remains 1,000 mG, i.e. 100,000 nT), but for a population judged more vulnerable, they choose an extra margin of safety, in the absence of total scientific certainty about the effects of low but prolonged exposure.
The ALARA principle
ALARA ("As Low As Reasonably Achievable") is a principle born in ionising radioprotection (X-rays, radioactivity), formalised by the International Commission on Radiological Protection in its Publication 26 of 1977. Its idea: even below the legal limits, it is good practice to reduce exposure as far as reasonably possible, meaning without disproportionate cost or constraint relative to the expected benefit.
Its application to non-ionising electromagnetic fields (low frequency, radiofrequencies) is more recent: research into the biological effects of non-ionising exposure, including at everyday levels, remains an active scientific field, with several studies pointing to effects worth taking seriously and monitoring closely. In this context of uncertainty, applying an ALARA approach is a precautionary step that many professionals in the field consider fully justified: it protects people, particularly the most sensitive, without waiting for science to settle every question definitively.
In practice, applying ALARA logic to an EMF audit means reducing what can reasonably be reduced: removing unnecessary sources (poorly placed chargers, powerline networking adapters, low-end dimmers), optimising wiring, and giving electrohypersensitive people as calm an environment as possible.
In summary
| Reference | Status | Purpose |
|---|---|---|
| ICNIRP / Belgian law (CENELEC) | Binding | Prevent well-established acute biological effects |
| Precautionary (Brussels children, EUROPAEM, BioInitiative) | Recommended, not binding | Margin of caution against scientific uncertainty |
| SBM / Baubiologie | Private comfort grid | Quality target for sleep areas |
A rigorous audit, then, is not about comparing a measurement to "the" standard, but about placing it honestly on these different scales, always specifying whether we're talking about low frequency or radiofrequencies, and explaining what the reference used does, and does not, represent.
This article stays factual and deliberately measured on health: none of these scales should be presented as establishing a causal link with any given illness, which is not recognised by any reference health authority (WHO, ANSES, Belgian Superior Health Council).
Sources
- ICNIRP, Guidelines for Limiting Exposure to Electromagnetic Fields (1998, 2010)
- Council of the European Union recommendation 1999/519/EC
- CENELEC, standards transposing the ICNIRP recommendations into Belgian law
- Walloon, Brussels and Flemish regional orders on exposure limits for electromagnetic waves
- EUROPAEM, EMF Guideline 2016
- BioInitiative Report (2007, 2012 revision)
- Institut für Baubiologie + Nachhaltigkeit, Standard of Building Biology Testing Methods (SBM-2024)
- Treaty on the Functioning of the European Union, Article 191
- International Commission on Radiological Protection, Publication 26 (1977)