Calculation of the risk index

The regulations UNE 21186, NFC 17102 and NP 4426 contain a method for assessing the risk of lightning, extracted from the international standard IEC 62.305-2, which determines the necessary protection systems. The following program is a simplified and automated version of this method, in order to make it more accessible to everyone. If a more precise calculation is required, or more complex structures, please contact us.

The aforementioned regulations include 3 parameters for calculating the risk index:

  • - The number of dangerous events per year.
  • - The probability of damage to a structure.
  • - The losses in case of damage.

1. Dangerous events are divided into 4 types, depending on how they can reach the structure:

  • - Events in the structure.
  • - Events near the structure.
  • - Events in power lines that affect the structure.
  • - Events near power lines that affect the structure.

2. The probability of damages is divided among three parameters:

  • - Direct injuries to living beings.
  • - Physical damage to the structure.
  • - Damage to electrical and electronic systems.

3. The losses are divided into 4 types:

  • - Human losses.
  • - Losses of service.
  • - Losses of cultural heritage.
  • - Economic losses.

Protection against lightning is necessary when the calculated risk exceeds the tolerable risk set out in the regulations.

Project data


 Made by:


 Phone number:



L, W, H

Dimensions in meters of the structure, which allow to calculate the area of lightning capture of the same.

 L1 (short side in meters):

 L2 (long side in meters):

 H: Height (m):

Hp: Extra height (Optional)

It is necessary in case of having a point very superior in height to the rest of the structure such as antennas, bell towers, towers, etc. Hp will be the height from the ground to the highest point.

 Hp (m):

 Ks1: Structure

Construction material of the structure, which provides electromagnetic shielding to the interior.

 Rf: Risk of fire

The risk of fire that the structure has, according to the material of its construction and its content.

Click on the point where you want to place the device

* Point chosen for the placement of the device.
* Farthest point to which the device should provide coverage.

Necessary protection radius: m.


 Ng: Density of impacts/year, km2

Number of lightning strikes per year per square kilometer in the area of the structure. If the value is unknown, enter it by taking it from this map or from the list of countries.

 Cd: Situation

The situation of the height of the structure with respect to the environment.

 Ce: Environment

The environment where the structure is located.

Electric lines

 PL: Situation of the cable

The situation of the electrical connection of the structure.

 PLD, PLI: EXternal cable type

If the electrical connection is shielded or not.

 Ct: Transformer

If the electrical connection has a transformer that protects from surges.

 Ks3: Type of intern cable

If the internal wiring of the structure is shielded or not.


Type 1: Human

 Lf1: Fire

The possibility of loss of human life caused by a fire, depending on the usual occupation.

 Hz1a: Panic

The possibility of loss of human life caused by panic, depending on the number of people, their mobility, etc.

 Hz1b: Environmental consequences

The possibility of environmental damage caused by possible contamination.

 Lo1: Surges

The possibility of loss of human life caused by surges, depending on the type of structure.

Type 2: Services

 L2: Losses of services due to fires and surges

The possibility that there are losses of public services and that subscribers see their service affected, according to sector.

Type 3: Cultural heritage

 Lf3: Losses of cultural heritage due to fire

The probability of cultural heritage losses due to fires.

Type 4: Economics

 Hz4: Environmental consequences

The possibility of economic losses caused by possible environmental contamination.

 Lf4: Fire

The possibility of economic losses caused by a possible fire.

 Lo4: Surges

The possibility of economic losses caused by surges.

 Lt4: Beasts situation

The possibility of economic losses due to the death of beasts, depending on whether or not they are inside the structure.


 Pb: Level of ESE lightning rod

If there is a lightning protection system according to the regulations, the level of protection it has.

 Pc: Surge arresters

If there is a surge protection system according to the regulations.

 Pa: Electric protection

The electrical protection measures for humans and animals.

 rp: Fire-fighting measures

The fire prevention measures that exist in the structure.


If you do not have enough information about it, do not modify the data that appears by default.

Lc: Cable length to the node
(max: 1000 m)

Hc: Cable height
(if air)

ra: Type of terrain

The type of terrain whose characteristics affect the human loss factor.

Lt1: Situation of humans

The location where humans can be with respect to the structure.

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