The short version
- Risk is judged per zone, not as one structure-wide total.
- Occupancy scaling is gone — a zone's risk is no longer diluted by its share of the building's people.
- The density input is the strike-point density NSG (from a lightning location system), with the older flash density NG as a fallback.
- Loss values were reorganised, and the old special-hazard factor is folded into them.
- Net effect: the same inputs can give a different verdict than a 2010-edition spreadsheet — by design, not by error.
1. Risk is evaluated per zone
The biggest structural change is how the verdict is formed. Under the 2024 edition, each risk zone is assessed on its own and compared against the tolerable risk RT; the structure needs protection if any zone exceeds its limit. There is no single structure-wide risk figure to compare — the per-zone truth is the assessment.
Practically, this means the way you divide a building into zones matters more than it used to. A small, high-consequence zone — a server room, an operating theatre — can drive the whole result even though it is a fraction of the floor area, because its risk is no longer averaged into the rest of the structure.
2. Occupancy scaling has been removed
The 2010 edition scaled a zone's loss of human life by the fraction of the structure's occupants present in that zone. In the 2024 edition that scaling is gone. A zone's risk stands on the danger present in that zone, not on how many of the building's people happen to be in it. This is the change most likely to move a number upward relative to an old calculation — risks that used to be diluted by a small occupancy share no longer are.
3. Strike-point density NSG, not just flash density
The event rates start from the lightning density at the site. The current edition works from the ground strike-point density NSG — the quantity a modern lightning location system reports (per IEC 62858) — rather than the ground flash density NG alone. Where only NG is available, it is converted with a factor; where you have satellite data, that is a last resort. If your old assessment plugged a flash-density map value straight in, that step now has an extra rung.
4. Loss values were reorganised
The typical loss values were restructured, and the separate special-hazard factor from the older edition is absorbed into the loss rows rather than applied on top. Physical-damage losses are treated as loss of property that is at risk whether or not people are present, so they are not weighted by time of presence. The upshot for a practising engineer is that the loss side of the calculation is read differently from the 2010 tables — one of the reasons a like-for-like comparison against an old worked example will not line up exactly.
What this means for your numbers
Put together, these changes mean a building assessed under Ed. 3 can land on a different verdict than the same building under the 2010 edition — most often a higher zone risk, because the occupancy dilution is gone and the consequence sits with the zone. That is not a tool disagreeing with a spreadsheet; it is two different editions of the standard. When you reconcile a new result against an old one, expect the per-zone structure, the occupancy treatment and the loss values to be where they diverge.
Run it on the current edition
Voltbench assesses lightning risk to IEC 62305-2 Ed. 3:2024 — per zone, each factor clause-cited, free on screen. See how it's validated.
This guide describes the method changes between editions in the authors' own words for practising engineers; it is not a reproduction of IEC 62305-2 and does not restate its tables. Always work from a current licensed copy of the standard. Voltbench is a calculation aid and does not replace the judgement of a licensed engineer of record.