What Changed in IEC 62305-2:2024, and Why It Matters for Your Facility

If your last lightning risk assessment was carried out against the 2010 edition of IEC 62305-2, the numbers behind it are now built on a superseded method. The third edition, published in 2024, cancels and replaces the 2010 second edition, and it is not a light touch-up. It changes how risk is defined, how the threat is counted, and what counts as a protection measure.

For owners and operators of critical and high-value infrastructure, that matters for a practical reason. A risk assessment is the document that justifies your protection spend, supports regulatory compliance, and underpins insurance and capital-approval conversations. When the standard behind it moves, an assessment that was sound a few years ago can quietly fall out of step, without anyone noticing until it is questioned.

Here is a plain-English walkthrough of what actually changed in the third edition, and why each change is worth your attention.

1. A single, combined risk

The previous edition treated different categories of loss as separate calculations. The 2024 edition introduces the concept of a single risk that combines loss of human life and loss due to fire into one assessment. Rather than evaluating these threads in isolation and reconciling them afterward, the standard now brings them together into a more coherent picture of the danger a structure faces.

The practical effect is a clearer, more decision-ready result. Instead of a set of separate figures that an engineer has to interpret and weigh, the assessment produces a unified view that maps more directly onto the question owners actually ask: how exposed are we, and is that exposure tolerable?

2. Frequency of damage to internal systems

The third edition introduces the concept of frequency of damage that can impair the availability of the internal systems within a structure. This is a direct acknowledgement that, for a modern facility, a lightning event does not have to cause a fire or threaten life to be a serious problem. It can simply take your systems offline.

For a data centre, a control room, or any operation where continuity is the whole point, this is the change that most closely reflects reality. Availability of internal systems, computer networks, and automation is now something the risk methodology speaks to directly, rather than treating downtime as an afterthought to structural and life-safety concerns.

3. N_SG replaces N_G: counting the threat more accurately

This is the change most likely to move your actual risk figures. The 2024 edition introduces lightning ground strike-point density, N_SG, replacing the older lightning flash density, N_G, in the evaluation of the expected average annual number of dangerous events.

The distinction is more than a relabelling. Ground strike-point density better represents how lightning actually reaches the ground, including the way a single flash can produce multiple strike points. The result is a more accurate basis for estimating how many dangerous events a given site can expect in a year, which feeds directly into the rest of the calculation. Two facilities that looked similar under the old flash-density metric can produce meaningfully different risk profiles under N_SG.

The catch is data. N_SG is only as good as the lightning data behind it, and the standard rewards a documented, consistent method over a single convenient number. This is precisely where the source of your lightning data, and the rigour of how it is applied, starts to matter.

4. Thunderstorm warning systems as a recognised measure

For the first time, the standard recognises that a few risk components can be reduced through preventive temporary measures activated by a thunderstorm warning system (TWS) compliant with IEC 62793. The third edition also introduces the risk of a direct strike to people in open areas, and accounts for the reduction of that risk where a TWS is in use.

This is a meaningful shift in thinking. Lightning protection has traditionally been about the fixed physical system: the air termination, the down conductors, the earthing, the surge protection. The 2024 edition formally acknowledges that advance warning, used to trigger safe operating procedures before a storm arrives, is itself a legitimate part of a risk-reduction strategy. It does not replace physical protection, but it can complement it, particularly where people work in exposed outdoor areas.

What this means in practice

Put together, these changes mean a risk assessment carried out properly under the third edition will often look different from its 2010-era equivalent, sometimes materially so. The combined-risk view, the focus on internal-system availability, and the move to N_SG can each shift the result. An assessment that predates the third edition is not automatically wrong, but it is built on a method the standard itself has now superseded.

If your facility is in a regulated sector, or if your protection decisions need to stand up to an auditor, an insurer, or a board, the edition behind your assessment is a fair question to ask. Three sensible steps:

• Check the edition. Find out which version of IEC 62305-2 your current assessment was carried out against. If it is the 2010 edition, it is a candidate for review.
• Look at your lightning data. An N_SG-based assessment depends on credible, well-documented ground strike-point data for your site, not regional averages or dated keraunic estimates.
• Consider continuity, not just life and fire. If your operation lives or dies on system availability, make sure your assessment reflects the third edition's treatment of internal-system damage frequency.

How Aetheric approaches it

Our risk assessment studies are carried out against the current third edition of IEC 62305-2, alongside AS/NZS 1768:2021. The analytical engine behind them is the LRAplus® platform from Skytree Scientific, a technology company co-founded to close exactly the gap this standard update highlights: the distance between a real-world site and the numbers used to assess it.

LRAplus® uses AI-powered calculation with real-time lightning location system data, so the strike-point density behind an assessment reflects measured activity at the facility rather than a regional estimate. That matters more under the third edition than it ever did before, because N_SG puts the quality of that data at the centre of the result. Skytree Scientific has published its own guide to navigating these standards for readers who want to go deeper on the methodology.

The short version: the standard has moved to reflect how lightning behaves and how modern facilities actually operate. The assessments that support your protection decisions should move with it.