Lightning Protection Parameters for High-rise buildings

 

With an increase of 85% in the number of apartments built in Ireland between 2002-2016, apartments accounted for 12% of all household types in 2016, compared to 11.1% in 2011 according to the Central Statistics Office.

According to the (CSO), there are now over 200,000 apartments occupied in Ireland, with the number increasing from 183,282 to 204,145, over the 2011-2016 period.

In Dublin City’s local area, apartments (74,537) became the main household type for the first time, replacing terraced houses. In the town of Clonee in County Meath, two out of every three households live in apartments.

The development of high-rise buildings continues to trend upward both in Ireland and Europe, with the average height of a high-rise building in Europe being 130 metres.

LPI’s Senior Electrical Engineer, Mr Hadi Beik Daraei, explains the lightning protection parameters for High-rise buildings including:

  • Direct strike probability
  • Building side flash
  • Spark and fire initiation source

High-rise Building Definition

A high-rise building is defined in technical guidelines and distinguished in some standards as a building above 5 floors or higher than 20-25 metres.

Lightning Protection Considerations for High–rise Buildings

 

Direct Strike Probability

The probability of exceeding a lightning current with a magnitude of 100 kA is 5 %. This means that 95 % of lightning strikes have a magnitude less than 100 kA.

A higher building leads to a higher possibility of a direct lightning strike, therefore the average flash density value could be varied at the building location. Accordingly, an increased probability of a higher (>30KA) or lower (<3KA) level of lightning current magnitude could occur.

As a rule of thumb, in an area with an average flash density greater than 1.5, for a building higher than 25 meters the risk of probable damage and loss of human life which contained more than 100 people is considered high risk. In this situation the protection of electrical or telecommunication equipment installed on the roof against a direct lightning strike is crucial.

Technical lightning protection diagram

Typical detail for LPS components in a high-rise building

 

Building Side Flash

On structures greater than 60 metres high, flashes to the building side elevations may occur, especially to points, corners, and edges of surfaces. Therefore, an air-termination system should be installed to protect the upper part of tall structures and the equipment installed on them.

The air-termination unit is typically installed to the topmost 20 % of the height of the structure as far as this part exceeds 60 m in height.

Spark and Fire Initiation Source

Lightning currents flow through a long conductor (i.e., Down Conductors), thus creating a vast number of voltages at one of its terminations ends. For this reason, the following issues need to be considered in lightning protection design for high-rise buildings:

  • Lightning discharge route design needs to be completed in such a way as to ensure the reasonable sharing of lightning currents between the down conductors. Therefore, using the rebars or steel structure as a supplement or main route of discharging the lightning current is a factor that impacts the types of bonding connections between down conductors.
  • The voltage difference may ignite the spark in the masonry in two ways:
    • between the down conductor and structure elements (columns or rebars).
    • between the structure elements (columns or rebars) and the possible metal structure which is located on the other side of the masonry.

Key Takeaways

  • According to the Central Statistics Office (CSO), there are now over 200,000 apartments occupied in Ireland, with the number increasing from 183,282 to 204,145 over the 2011-2016 period.
  • A higher building leads to a higher possibility of a direct lightning strike.
  • In an area with an average flash density greater than 1.5, for a building higher than 25 meters the risk of probable damage and loss of human life which contained more than 100 people is considered high risk.
  • On structures greater than 60 metres high, flashes to the building side elevations may occur, especially to points, corners, and edges of surfaces.
  • The air-termination unit is typically installed to the topmost 20 % of the height of the structure as far as this part exceeds 60 m in height.
  • Lightning discharge route design needs to be completed in such a way as to ensure the reasonable sharing of lightning currents between the down conductors.
  • The voltage difference may ignite the spark in the masonry between the down conductor and structure elements (columns or rebars), and between the structure elements (Columns or rebars) and the possible metal structure which is located on the other side of the masonry.

What LPI Group Can Offer

LPI Group can offer clients turnkey solutions in lightning protection design including Surge protection studies and supply and install of surge protection devices for already established premises.

Fill out the contact form to to talk to our technical design team about your lightning protection system.

LPI Group – Cloud to Ground Protection for Your Industry

By Hadi Beik Daraei, Senior Electrical Engineer at LPI Group