Protecting Buildings against Lightning Strike and EMP
01-12-2022 | Posted by Joaquín Martí
This post is extracted from one recently published by Dassault Systèmes.
As soon as we are left without WiFi, we realise how dependent we are on being connected. Hence, the buildings providing that connection and storing our data must be protected against unintentional or intentional electromagnetic (EM) events.
Lightning can be beautiful, but it has its downsides. It occurs when an electrical charge builds up on water or ice particles within a storm cloud and the electric field becomes sufficiently high to ionize the air. The region of ionized air develops ‘stepped leaders’, a step-like series of charges that branch their way down. When a stepped leader gets close to the ground, an oppositely charged ‘streamer’ rises to meet it and establish a conducting channel between cloud and ground. This discharges the cloud by enabling a current pulse to flow, which we see as a flash; it can reach tens, even hundreds, of thousands of amps and is extremely hot (up to 30 000ºC), causing a rapid expansion of the surrounding air and a shock wave that we hear as thunder.
A tall metallic building may offer a good path for lightning. The building will then become part of the lightning channel and be exposed to the intense current, which contains sufficient energy to cause significant heating and structural damage. The magnetic fields associated with the current can induce harmful currents and voltages in cabling and electrical/electronic systems, causing the destruction of sensitive electronic components.
Electromagnetic pulse (EMP)
EMP can occur naturally or because of human activity. A natural occurrence is a solar EMP, caused by a burst of plasma, and its embedded magnetic field, being ejected from the solar corona. A man-made EMP occurs as a result of a nuclear explosion due to particles interacting with the earth’s atmosphere and magnetic field.
EMP generates high-intensity EM waves with peak electric field levels of tens of kilovolts per metre. These waves can enter buildings through windows, seams around doors, air vents, pipes, and cabling. Once inside, EMP-generated fields couple to electronic systems and can damage devices and destroy stored data.
Protecting digital infrastructure
Lightning protection partly involves diverting current away from sensitive systems; for example, a lightning rod may collect the lightning at a controlled location and conduct it to the ground safely.
Shielding is used to prevent low-frequency magnetic fields from diffusing through building materials and may also be applied to cabling. EMP protection generally involves ensuring that apertures are kept smaller than the EMP wavelengths and applying shielding to create protected zones. Conductive gaskets are installed in seams to remove apertures, and conductive coatings can be applied to windows to attenuate field transmission through the glass material.
Filtering and transient protection devices may be used to attenuate or clamp the voltages and currents at connector interfaces. Metallic mesh in utility pipes can filter electromagnetic waves and prevent them from entering the building.
Simulation enables evaluating lightning/EMP vulnerabilities before constructing a new building or hardening an existing one. Different protection schemes can be analysed to assess their effectiveness, study design trade-offs, and reduce costs.
A multi-disciplinary approach ensures that EM protection features do not impair structural integrity or cooling system performance, or vice-versa. For example, metal piping deployed as part of the cooling system could potentially act as a conduit for electromagnetic fields and currents and could even enhance the fields, and worsen the damage, due to electromagnetic resonance effects.
Modern simulation techniques using the Virtual Twin open new avenues for innovation by giving the engineer a full understanding of the entire system. Simulation with CST Studio Suite technology enables visualising fields and coupling paths, providing insight into the performance of the building, leading to optimal design and protection. By accessing SIMULIA EM simulation technology through the 3DEXPERIENCE platform, all stakeholders work with up-to-date data, maintaining continuity from design to simulation to manufacturing.