The last post talked about the probability of a lightning strike for steel buildings with metal roofing. As can be deduced from the list, this probability is more or less the same for any other kind of structure. The probabilities have a lot to do more with the height and size of the structure, its location, and its surroundings, rather than the type of materials used in buildings’ construction.

What are the possible consequences if lightning does strike a building? A lightning strike pose threats to human life, damage to the contents of the building and to the steel building itself. The severity of these threats and the consequences of a lightning strike, are affected by a lot of factors such as:

1. The kind of construction materials used for both framing and roof coverings – Threats of fire, explosion, and therefore, to human lives, are greatly reduced if the construction materials used are electrically conductive. Also, threats are further reduced if these materials are non-combustible because they will not contribute as fuel source to any fire resulting from a lightning strike.

2. Physical contents of the building – Flammable or explosive contents, obviously increases the risks of fires. Besides, if the contents are highly sensitive, valuable and irreplaceable, the consequence of loss is magnified.

3. Human occupancy – Buildings which are heavily occupied, are considered high risk. In addition, the risk to human life further increases if the occupants are handicapped or non-ambulatory and are incapable of quick evacuation.

As can be inferred from the above discussion and the post yesterday, metal roofing is the most desirable type of roofing system for steel buildings because it is both an electrical conductor and a non-combustible material.

Another point worth mentioning is the fact that steel buildings provide reduced risks to fire and explosion due to a lightning strike, because steel is an electrical conductor and a non-combustible construction material.

Source: http://www.metalconstruction.org/pubs/pdf/1040%20Lightning%20Metal%20Roofing.pdf

Some people are under the impression that using metal roofing for steel buildings heightens the probability of lightning strikes to the metal structures. On the other hand, it has been found that metal roofing does not increase this risk.

Lightning is an atmospheric discharge of electricity accompanied by thunder or a flow of electrical current between earth and sky. Most experts agree that the route for a lightning strike begins from the clouds and extends earthward. However, there are instances when the route of the strike starts from earth to sky.

Just like any flow of electrical current, lightning follows the path of least resistance. The heat energy that is generated by the resistance to the flow of electricity is the one that causes explosions, fires, and other damage.

The probability of lightning strikes to steel buildings with metal roofing, is determined by a number of factors:

1. Topography of the area where the structure is located – The probability of a lightning strike for a steel building is higher if it is built on a mountaintop or hilltop as opposed to a field.

2. Size and height of the steel building – A tall steel building or one covering more ground area is more likely to be struck than a short or small building.

3. Relative location of the steel building with respect to nearby larger and taller structures – The presence of a very tall structure in proximity to a small and short steel building will tend to further reduce the likelihood of a strike to the small building.

4. Frequency and severity of thunderstorm activity in the geographic area of the steel building.

(to be continued)

Source: http://www.metalconstruction.org/pubs/pdf/1040%20Lightning%20Metal%20Roofing.pdf