We’ve talked a lot about lightning protection but not actually about the phenomenon of lightning itself to understand how protection works its worth having a look at why and how lightning strikes.
The lightning most frequently referred to in terms of lightning protection is cloud to ground lightning, other forms of lightning exist but cause less damage to buildings and people than this particular recognised form of lightning.
A lightning strike originates about 15,000 to 20,000 feet above sea level and works its way down to about 50 yards above ground, it’s about at this height that will determine the attachment point which is the point where lightning will strike. The currents in lightning range up to 400kA with average individual stroke of lightning ranging between 25kA to 40kA, the total current will be divided between the different paths of the lightning strikes.
When lightning strikes a stepped leader works its way towards the ground and is met by an upward leader that comes from the ground then a number of return strokes occur which are flashes from the point of contact to the cloud.
Lightning strikes cannot be prevented, they can only be intercepted or diverted onto a path that if well designed will not result in damage, injury or loss of life. Any designed path to earth should have a low impedance connection to earth; this means that the opposition to the flowing current should not be high. The measure is calculated using a complex formula but a protection system can be designed to have low impedance connection.
Lightning protection should always be installed by certificated ATLAS accredited lightning protection designer, if this is not possible measures should be taken to ensure that the installation is assessed by a suitably qualified ATLAS company and that the lightning protection installation will work and protect the building and its occupants against the effects of a lightning strike.
To discuss your lightning protection requirements email our design team at firstname.lastname@example.org