From the first article “The Story of Lightning Part 1”, we know that lightning is a natural phenomenon caused by static electricity. We also noted that there are several religious and cultural beliefs associated with lightning and the devastation caused by lightning.
From the second article “The Story of Lightning Part 2” the devastation to human lives was discussed. The “Big Killers of a Lightning Strike” were also identified. We learnt about the correct safety action/position to take if we are caught outdoors during a thunderstorm.
The American National Weather Service slogan “When Thunder Roars Go Indoors” remains very good advice. However, it should be noted that not all buildings are lightning safe and therefore we need to remain vigilant and aware of what is happening around us. In this article, I will discuss what lightning safe buildings are.
INDOOR DEATHS DUE TO LIGHTNING:
A Times Live article headline, written on 3rd March 2017 was titled “Three sisters were declared dead after being struck by lightning while they were at home alone in the Eastern Cape” (South Africa).
Traditional African houses, with reed or thatched roofs and no LPS (Lightning Protection System), do not provide much protection against lightning strikes. Most of these houses are situated in rural areas, a long distance from Fire Protection services. This does not imply that all thatched roof houses are death traps in a thunderstorm, if they are equipped with a correctly designed, installed and certified LPS system they can be quite safe.
Below is a picture of a traditional African house, in a rural area that was destroyed due to lightning. Often when lightning strikes these houses, catch alight and burn down to the ground in an incredibly short period of time. In most instances the occupants do not have sufficient time to flee the house safely, resulting in deaths.
From Kreci, Albert, Gentian Vyshka, and Admir Sinamati
Indoor deaths, due to lightning, occur all around the world. In an article published by Kreci, Albert,
Gentian Vyshka, and Admir Sinamati “Lightning Injuries in an In-door Setting” A Case Report and Review of the literature published in the Journal of Environment Pollution and Human Health in 2013, the case study lists a man that was killed in the kitchen of his house in Albania. The man was killed while attending to the wood burning stove, when the lightning struck the steel pipe that was used as a chimney. The picture below shows the damage cause by this incident.
From Manchester Evening News
OTHER INDOOR DAMAGES CAUSED BY LIGHTNING:
A Manchester Evening News article headline, written in 23rd July 2013 was titled “Church in Ramsbottom (UK) badly damaged by lightning strike”. The picture below shows the extent of this damage and people could have been injured, if they were in the church at the time.
From Bothwell Electrical
INDOOR ELECTRICAL DAMAGES CAUSED BY LIGHTNING:
Quite often when lightning strikes, direct strike or nearby strike, a high surge voltage is generated in electrical wiring systems. This can be cause by induced electromagnetic coupling between earthing/grounding conductors and live phase conductors. It should also be noted that there will be a rise in the earth/grounding potential. If no SPD (Surge Protective Device) has been installed, these surge voltages can cause extensive damage to the electrical wiring systems within buildings and may result in fires. The picture below gives an indication of this type of damage.
LIGHTNING SAFE BUILDING:
The best form of protection against Lightning is a Faraday cage, for this reason metallic motor vehicles with enclosed roofs are Lightning Safe. As for buildings to be lightning safe, they require full integrated LPS (Lightning Protection Systems).
Home owners are very resourceful and like to take on DIY projects, however Lightning Protection Systems for homes are not to be attempted as a DIY project. A half completed LPS system can be extremely dangerous and increase the Risks to which we are exposed. All LPS systems must be designed, installed, and certified by a reputable professional contractor.
A Lightning Protection System is an implementation of a process, as follows:
1. Lightning Risk Assessment, even if this is a short form assessment and not the full SANS/IEC 62305 type risk assessment. The assumptions and the Lightning Protection Level, needs to be documents and the client needs to sign acceptance of the risk assessment.
2. The Lightning Protection Level will then determine the spacing and number of Air Terminals that are required. When Air Terminals are installed on a building, a minimum of two parallel paths are required for the Down Conductor System, possibly situated at opposite ends of the building.
3. A suitably rated Down Conductor System, taking into account the required separation distances. These down conductors must be correctly secured to the building, and are normally installed in insulated PVC pipe for the first 2 m above the ground. These down conductors often terminate at a test link, where they are connected to the Earth Electrode System.
4. Before the Earth Electrode System is designed, it is advisable to conduct Soil Resistivity tests to establish the Soil Model. If Soil Resistivity tests are not conducted, it becomes a trial and error type situation and a lot of time and money can be wasted. The Earth Terminal System also needs to be adequately rated and normally is either a Type A or Type B configuration
and can consist of trenched electrodes and/or vertical rod electrodes.
5. The Earth Terminal System of the Lightning Protection System, must be bonded to the buildings earthing/grounding system. This is to ensure an equipotential earthing system, and limit high Touch Potentials between different equipment.
6. Where required, as a mitigating factor in the Lightning Risk Assessment, Surge Protective Devices must be installed. Surge Protective Devices need to be correctly coordinated, where different classes of Surge Protective Devices are installed. Where the prospective short circuit fault current is higher than the rating of the Surge Protective Device, then correctly
rated Pre-Fusing must be installed.
7. Once the Lightning Protective System has been installed and tested, the correct certification needs to be issued to the client. In terms of the South African requirements a “Certificate of Safe Installation” as per SANS 10313, this is not a CoC (Certificate of Compliance). As per South African legislation (Electrical Installation Regulation R242-March 2009), if Surge
Protective Devices are retrofitted into any Distribution Board, a revised/amended CoC (Certificate of Compliance) must be issued for the additions/modifications to the “Electrical Installation”. The revised/amended CoC must then include the “Certificate of Safe Installation”, which is Annexure I in the SANS 10142 wiring code. The certification requirements may be different for other countries and therefore the local requirements need to be checked.
8. Where roof top PV (Photovoltaic) systems are installed, special Lightning Protection Systems are required. These systems are referred to as “Isolated Lightning Protection Systems”. The wiring code (SANS 10142) requires that the PV panels be directly connected to the house/building earthing system. In the event of a direct lightning strike to the PV panel, the full lightning current will be earthed via the buildings wiring system and the Distribution Board. For this reason, an “Isolated Lightning Protection System” is required. This type of system, by means of correct placement of Air Terminals, will prevent a direct lightning strike to the PV panel, the lightning current then flows to earth via the Down Conductor System. The Earthing systems are then bonded at ground level and this prevents the full lightning current from flowing via the buildings wiring system.
LPS systems require an integrated approach and need to cover the full spectrum of the requirements. A phased LPS installation, were the installation is done in stages with time gaps between the stages, can lead to dangerous situations. That is, we can’t install Air Terminals Systems without Down Conductors Systems, Earth Termination Systems, Equipotently Bonding and possibly Surge Protective Devices.
SAFETY INDOORS DURING A THUNDER STORM
To go back to the unfortunate death in the house in Albania, although I doubt if it was the intention to use the steel pipe chimney as an Air Terminal System, the chimney did act as an Air Terminal System, and without proper Down Conductor System and Earth Termination System in place this became a lethal installation.
It is only by means of a Lightning Safe Building/Structure, that we can ensure safety indoors. Even though it is a Lightning Safe Building, we still need to take the following additional safety measures:
1. Stay away from electrical plug sockets and fittings;
2. Do not use landline telephones;
3. Do not touch water pipes or take a bath/shower. If the equipotential bonding has been done
correctly, this may not pose a danger, however if the bonding is faulty, this could then
become lethal. It is really NOT worth taking a chance.
4. Stay away from windows and metallic door frames.
5. Be alert to the possibility of fires. Ensure that there is a plan of escape in the event of a fire
and have fire extinguishers available.
In the next article, I will review the effects lightning has on outdoor sporting and recreational events.