{
  "id": "protocols:elf-magnetic-survey",
  "collection": "protocols",
  "slug": "elf-magnetic-survey",
  "name": "ELF magnetic field survey",
  "summary": "A source-finding walkthrough plus a 24-hour log, because power-frequency magnetic fields track electrical load and a spot reading answers almost nothing.",
  "status": "verified",
  "lastVerified": "2026-08-12",
  "data": {
    "aliases": [
      "how to measure milligauss",
      "gaussmeter survey"
    ],
    "goal": "Find the source of any elevated 50/60 Hz magnetic field and quantify exposure at sleeping and working positions over a full day.",
    "quantity": "magnetic-flux-density",
    "equipment": [
      "elf-gaussmeter",
      "data-logger"
    ],
    "steps": [
      "Record meter model, axis configuration and frequency response.",
      "Walk the perimeter of each room with the meter at waist height, noting every local maximum and its apparent source.",
      "Measure at 0.3 m, 1 m and 3 m from each candidate source to confirm the inverse fall-off that identifies a compact source.",
      "Check the service panel, meter base, and both sides of every wall that backs onto one.",
      "If readings are elevated everywhere and do not fall off with distance, suspect net current on the neutral or a shared neutral, and involve an electrician.",
      "Log continuously for at least 24 hours at the pillow position, sampling at least once per second where the instrument allows.",
      "Report the mean, the night-time mean and the 95th percentile, not just the maximum."
    ],
    "pitfalls": [
      "Spot-reading at one time of day, when line and household loading vary by several times",
      "Using a single-axis meter and rotating it inconsistently",
      "Assuming shielding is the fix; magnetic fields pass through nearly all common materials",
      "Missing a wiring fault, which is the one cause that raises the whole building and cannot be solved with distance",
      "Using a 50/60 Hz-only meter near inverters, EV chargers or induction hobs, where the energy is in the kilohertz range"
    ],
    "interpretAgainst": [
      "limits:sbm-2024-magnetic-bands",
      "limits:who-elf-leukaemia-association",
      "limits:icnirp-2010-public-magnetic-50-60",
      "limits:ch-onir-power-lines"
    ],
    "related": [
      "emitters:electrical-service-panel",
      "meters:elf-gaussmeter"
    ]
  },
  "sources": [
    {
      "id": "sbm-2024",
      "title": "Building Biology Evaluation Guidelines for Sleeping Areas (SBM-2024)",
      "publisher": "Institut für Baubiologie + Nachhaltigkeit (IBN)",
      "url": "https://buildingbiology.com/site/downloads/SBM-2024_EVALUATION_GUIDELINES_EN.pdf",
      "year": 2024,
      "kind": "ngo",
      "retrieved": "2026-08-12"
    },
    {
      "id": "niehs-emf",
      "title": "Electric and Magnetic Fields",
      "publisher": "National Institute of Environmental Health Sciences",
      "url": "https://www.niehs.nih.gov/health/topics/agents/emf",
      "kind": "government",
      "retrieved": "2026-08-12"
    },
    {
      "id": "who-elf",
      "title": "Electromagnetic fields and public health: exposure to extremely low frequency fields",
      "publisher": "World Health Organization",
      "url": "https://www.who.int/teams/environment-climate-change-and-health/radiation-and-health/non-ionizing/exposure",
      "year": 2007,
      "kind": "government",
      "retrieved": "2026-08-12"
    }
  ],
  "links": {
    "self": "https://emfbase.com/api/protocols/elf-magnetic-survey",
    "html": "https://emfbase.com/protocols/elf-magnetic-survey",
    "markdown": "https://emfbase.com/protocols/elf-magnetic-survey.md",
    "collection": "https://emfbase.com/api/protocols"
  }
}