Written by Ian Richardson, National Sales Development – Surge & Lightning Protection
The Australian Standard for Lightning Protection, AS 1768:2021, provides the requirements for lightning protection for a wide range of structures and systems.
The 2021 edition of AS 1768 saw a major revision in comparison to previous editions, to align more closely with the global IEC standards. Whilst AS 1768:2021 compliance will not necessarily prevent damage to assets or personal injury, it will reduce the probability of damage and injuries.
The standard acknowledges that thunderstorms and lightning are natural phenomenon and largely unpredictable. The effects of a single lightning strike can be felt over a wide area and the standard states that almost half of all cloud to ground flashes have more than one ground termination, typically two, separated by distances of up to 10 kilometres.
To assist in reducing the risk of damage and injuries caused by a lightning strike, AS 1768 included an excellent risk assessment tool which compares a calculated risk against a tolerable risk level, however the standard also notes that protection measures may be justified regardless of the outcome of the risk assessment.
A fundamental consideration of the risk assessment is the average annual lightning ground flash density (Ng), taken from a map by the Australian Bureau of Meteorology (BoM) and reproduced in the standard. This map is available on the BoM website. The map broadly defines the lightning risk of areas of Australia to be used in the risk assessment. It is often recommended that areas with an Ng value of 2 or greater should consider a lightning protection system, equipotential bonding and the installation of surge protection devices.
The lightning ground flash density is defined as the number of ground flashes per square kilometre, per annum. So, to put it simply, in an area designated with an Ng value of 2, on average there could be 2 ground flashes (lightning strikes) every year in each square kilometre. Leading to the question regarding tolerable risk. Is a defined risk of even one lightning strike per kilometre each year a tolerable risk, given the potentially devasting effect on people, assets, and lost production?
Climate change is an ongoing debate and concern in the global community. Many scientists believe lightning frequency is changing, as the climate is changing. According to the University of WA lightning fact sheet published in 2010, it is reported that many scientists predict global warming will increase the number of severe storms around the world, in turn resulting in more lightning strikes. They go on to say this could potentially be up to three times more than the current number of lightning strikes.
We design our buildings and electrical systems for a long-life expectancy. When conducting a risk assessment according to AS 1768 it is recommended that you consider the facts beyond the basic risk assessment. The standard even advises the decision to provide lightning protection requires judgement on the part of the user.
The reality of our future is that the risk of lightning is likely to increase in coming years and the need to protect assets through lightning protection and surge protection measures will surely increase. Generally, the cost of lightning and surge protection solutions is small compared to the asset it is protecting. Well worth considering.