Why has Sweden become, since the 1990s, the world reference for electromagnetic precaution? And what does that have to do with your laptop's USB-C cable? A dive into a Swedish story that still sheds light on our practices today.
The starting point: a study that changed the debate
In 1993, two researchers at the Karolinska Institute in Stockholm, Maria Feychting and Anders Ahlbom, published a study that would durably mark the debate on low-frequency electromagnetic fields. Their method: track an entire generation of children who had lived within 300 metres of a high-voltage power line (220 or 400 kV) between 1960 and 1985, and cross that data with the national cancer registry.
The result, published in the American Journal of Epidemiology, did not go unnoticed: among children exposed to a calculated magnetic field above 200 nanotesla (nT), the relative risk of leukaemia was multiplied by 2.7. Above 300 nT, it rose to 3.8. Notably, no similar association was found for central nervous system tumours or for childhood cancers as a whole, a result specific to leukaemia that fuelled nearly thirty years of scientific debate, until the IARC classified low-frequency magnetic fields as "possibly carcinogenic" (Group 2B) in 2001.
Sweden's response: no law, but a doctrine
Here is what makes the Swedish case so interesting: this study never led to a law setting a mandatory minimum distance. Sweden made a different choice, and, in hindsight, a rather visionary one.
As early as 1996, four national authorities published a founding guide, "Low-frequency electrical and magnetic fields: The precautionary principle for national authorities", setting out a simple principle: act with precaution on risks that science has not ruled out, without waiting for definitive proof.
Today, the Swedish radiation safety authority (Strålsäkerhetsmyndigheten) translates that principle into concrete recommendations: design and position new electrical installations to limit exposure, avoid siting schools, nurseries and housing near high-field installations, and reduce fields that deviate significantly from normal, provided this remains economically reasonable.
The national grid operator, Svenska kraftnät, has even translated this doctrine into a numerical target, purely internal and not legally binding: aim for a magnetic field below 400 nT near permanent residences when designing new lines. This is, almost point for point, the risk zone identified by Feychting and Ahlbom two decades earlier.
The lesson to remember: Sweden clearly distinguishes two logics that are too often conflated in Belgium, the regulatory limit (100,000 nT, the ICNIRP/EU threshold) and the precautionary level (400 nT, a policy choice aimed at reducing persistent scientific uncertainty). These are not the same thresholds, the same objectives, or the same legal basis.
The same country, another battle: computer screens
Sweden did not only legislate (or rather, not legislate) on high-voltage power lines. As early as the start of the 1990s, the Swedish trade union confederation TCO imposed electromagnetic emission standards for computer screens on the whole world, well before anyone spoke of "precaution" for the general public.
The TCO standard, through its successive versions (TCO'92, '95, '99, '03, '06), set two constant thresholds for nearly three decades, measured at 30 or 50 cm from the screen:
- Low-frequency band (5 Hz – 2 kHz): 10 V/m electric field, 200 nT magnetic field
- Very-low-frequency band (2 kHz – 400 kHz): 1.0 V/m electric field, 25 nT magnetic field
These values are deliberately far stricter than generic regulatory thresholds; the TCO logic was never that of a legal framework, but of a quality and comfort label, driven by a private actor that ended up shaping an entire industrial sector.
Coming full circle: the unexpected return of the problem
Here is the most striking part of this story: the problem was thought settled since the demise of the cathode-ray tube screen. Flat screens (LCD, LED) no longer have an electron beam and, in theory, emit far less low-frequency electric field.
But a recent European directive, motivated by ecological objectives, ended the requirement for a grounded USB-C cable. An unintended consequence: some laptops, the MacBook being the most documented example, are reintroducing measurable low-frequency electric fields, exactly within the band that the TCO standard had capped at 10 V/m for three decades.
In other words: a problem the industry thought it had solved through a thirty-year-old Swedish standard is resurfacing, not because of any relaxation of electronic requirements, but because of a regulatory choice made for an entirely different objective (cable ecology). It is a near-perfect textbook case of what electromagnetic engineering calls an "unanticipated consequence", and a reminder that vigilance on these subjects is never settled once and for all.
These two Swedish stories (high-voltage power lines and computer screens) illustrate the same truth: managing electromagnetic fields is as much a matter of societal choice as of pure science. Understanding the difference between a regulatory standard and a precautionary level is already half the work of an electromagnetic environment consultant.
Sources
- Feychting & Ahlbom, Magnetic fields and cancer in children residing near Swedish high-voltage power lines, American Journal of Epidemiology (1993)
- International Agency for Research on Cancer (IARC), classification of low-frequency magnetic fields, Group 2B (2001)
- Swedish national authorities, Low-frequency electrical and magnetic fields: The precautionary principle for national authorities (1996)
- Strålsäkerhetsmyndigheten (Swedish Radiation Safety Authority), recommendations on low-frequency electromagnetic fields
- Svenska kraftnät, internal design target for new high-voltage lines
- TCO Development, TCO'92 to TCO'06 standards on electromagnetic emissions from computer screens