The level of lightning protection a system requires is never determined by guesswork. Which building needs which level of protection is calculated through a risk assessment carried out under TS EN / IEC 62305-2. The tool on this page is a preliminary assessment aid, designed to give you a quick view of your building's risk profile.
Why Is a Risk Assessment Necessary?
Two neighbouring buildings, on the same street and of the same height, can still require entirely different levels of protection. One might have ten people working inside it, the other two hundred; one might hold standard office equipment, the other a control system that halts production the moment it stops. Risk has less to do with the building itself than with what's inside it.
For this reason, the standard does not lay down a simple rule such as "a building of this height needs this system." Instead, it produces a numerical risk value by jointly assessing the building's location, dimensions, materials, purpose, the density of people and equipment inside it, and the local lightning density. Where this value exceeds the threshold the standard considers acceptable, protective measures become mandatory.
Four Distinct Risks Are Assessed
TS EN / IEC 62305-2 addresses the loss lightning can cause under four headings. Not every heading needs to be calculated for every building; which risks apply depends on the nature of the building itself.
Risk of Loss of Human Life
The risk of loss of life or permanent injury. This is assessed for every building and carries the lowest tolerance threshold of the four risks.
Risk of Loss of Service
Interruption of a service provided to the public. Applies to infrastructure such as power distribution, telecommunications, and water supply.
Risk of Loss of Cultural Heritage
Loss of assets that cannot be replaced. Assessed for museums, historic buildings, and archives.
Risk of Economic Loss
The financial value of the building, its contents, and lost production. Assessed together with a cost-benefit analysis of the protection investment.
What Goes Into the Calculation?
- Dimensions of the building — Length, width, and height; these determine the collection area
- Location and surroundings — Neighbouring structures and terrain conditions
- Local lightning density — The number of lightning strikes per square kilometre per year
- Roof and wall materials — Affect fire risk and conductivity
- Intended use — Residential, office, industrial facility, hospital, school, data centre
- Number of occupants and time spent inside — The primary input for the risk of loss of human life
- Fire load and explosion risk — The nature of the materials present on site
- Connected service lines — How power, telecom, and data lines enter the building
- Existing protection measures — The current state of any external lightning protection, SPDs, and earthing
The Result: Lightning Protection Level (LPL)
The output of the calculation is the Lightning Protection Level that must be applied to the building. The standard defines four levels; as the level rises, the air termination system becomes denser and protection becomes more comprehensive.
| Level | Rolling Sphere Radius | Mesh Spacing | Typical Application |
|---|---|---|---|
| LPL I | 20 m | 5 × 5 m | Explosives facilities, critical infrastructure, hospitals |
| LPL II | 30 m | 10 × 10 m | Industrial facilities, schools, data centres |
| LPL III | 45 m | 15 × 15 m | Commercial buildings, office buildings, warehouses |
| LPL IV | 60 m | 20 × 20 m | Low-risk buildings, residences |
The placement of the air terminals is determined by these values. Under LPL I, any point a 20-metre sphere can touch on the building is treated as unprotected; under LPL IV, that radius extends to 60 metres. This difference directly affects how dense the air termination system needs to be.
What This Tool Does — and Doesn't Do
This calculator gives you a quick, preliminary picture of your building's risk profile and indicates which protection level is likely to apply. It does not, however, replace a formal risk assessment report.
A risk assessment prepared under TS EN / IEC 62305-2 requires a site survey, review of the architectural and electrical drawings, and engineer sign-off. This report is what design, permitting, and inspection processes are based on. If your preliminary assessment points to a risk, contact us for the next step.
Calculate your building's lightning risk using the simplified method of TS EN / IEC 62305-2. You'll get a result in four steps, and you'll see it before submitting any information.
