We Wrote The Book on Grounding and Earthing

Toll Free: 888.367.0888

Ask The Experts Blog

Is it safe to use structural steel as a down conductor for a Lightning Protection System at a school?

Alan is from England and tells us:

I have concerns for my grandson’s safety regarding the method of lightning protection used at his new school. They have not used the conventional copper down conductors but have instead used the steel columns, which have also been painted which, in my view increase the dangers of the strike.

These VERTICAL steel coloumns are NUMEROUS and strategically located INSIDE the building and within touching distance of pupils.  There are numerous other steel objects as integral part of the school which have not been bonded to the LPS: steel downpipes, steel windows, steel staircase, floodlights, etc.

My limited knowledge of the LPS specifications are that the Steel Structures can be used but they must be insulated or isolated to the first 3 meters.  I hope you can reasure me on this matter.

Hi Alan,

Thank you for your question regarding Lighting Protection Systems (LPS) in public buildings.  It is our pleasure to help.

It sounds from your email that you are quite frustrated by the lack of response from your grandson’s school.  We have found that lightning is an underrated risk in the eyes of the public, as single lightning events typically claim only one or two victims per incident and generally causes only localized destruction.  Lightning strikes are a very serious and dangerous natural phenomenon; we hope that our response will alleviate some of your concerns.

To start, here are a few interesting statistics about lightning strikes:

  • Lightning can generate temperatures in excess of 50,000 degrees Fahrenheit
  • Lightning bolts have been measured to have as much as 200,000 amps and from 100 Million to 1 Billion volts (from cloud to earth)
  • As you read this, there are some 1,800 thunderstorms occurring somewhere on the earth equating to 16 million storms each year.
  • In the United States alone, electronic monitoring devices record an annual average of 25 million flashes of lightning from the cloud to ground
  • It has been estimated that there are 100 lightning strikes per second, or 8,640,00 times a day, occurring somewhere on the planet
  • Annually, lightning kills more people than tornadoes, hurricanes or winter storms. It is second only to flash floods in deaths from annual storm-related hazards.
  • The Federal Emergency Management Agency (FEMA) estimates there are 750 severe injuries and 200 deaths in the U.S. from lightning each year
  • In the U.S. the odds of becoming a lightning victim in any one year is 1 in 700,000.  In your lifetime the odds of being struck by lightning is 1 in 3,000.
  • 20% of all lightning strike victims die
  • 70% of survivors will suffer serious long-term injuries
  • 85% of lightning victims are young men and children between the ages of 10 and 35 engaged in outdoor activities
  • More than 10,000 forest fires caused by lightning annually
  • In the U.S. lightning causes an estimated $4-5 billion in damage annually

We relay this information primarily to inform you that you are right to be concerned.  However, you are quite fortunate to be located in the British Isles.  England is arguably the world leader in lightning protection and has codified it’s knowledge in the excellent BS EN 62305:2006 document.  While this document itself is quite cumbersome, the following link will summarize its contents.  Please note under section 3 that there are very specific requirements for using steel columns as part of the lightning protection system.

http://www.esgroundingsolutions.com/about-electrical-grounding/lightning-protection-systems-nfpa-780.php

We would recommend that you contact your grandson’s school and ask for a copy of the Risk Factor Assessment as required under BS EN 62305:2006.  Rest assured, if the Lightning Protections System (LPS) for the school was built in accordance with BS EN 62305:2006, your grandson is safe.

Now, to your point about the steel columns being within touch range of the children; this is called Touch Voltage.  While it is a difficult concept to understand, the situation is not that different from why birds on a high-voltage wires and not electrocuted; there is no voltage difference between the birds feet.  Now, if the bird were to straddle two separate wires… that would be a well cooked bird.

The same is true for humans as long as there is no difference in potential between the feet and hands.   The students at the school will be quite safe as long as the steel rebar in the concrete is bonded to the LPS (as required under BS EN 62305:2006).  In fact, for certain situations, adding insulation can actual generate voltages that would not have existed without the added resistance.   The following link talks about Touch Voltages and other Human Safety hazards:

http://www.esgroundingsolutions.com/about-electrical-grounding/what-is-step-and-touch-potential-and-resistance-to-ground.php

Now with all of the above said, we agree with you in principle; that LPS’ should be designed to protect the building by directing as much of the lightning energy away from the structure as possible.  Using the building as a conductor goes against that fundamental principle and unnecessarily places lightning energy directly into a structure and all its electronic equipment.  But then again, there is a long and successful  history of structures using building steel as part of the LPS.  While it may seem that your grandson’s school has chosen this Lightning Protection method simply to save money (and it may well have), you should know that the method does in fact work, when done properly.

We hope you find this information useful.  If you should have any further questions or concerns, please do not hesitate to call during normal working hours (California time) and one of our engineers will be glad to speak with you , free of charge.

Best regards,

The Engineering Team at E&S Grounding Solutions

Photo credit: http://www.flickr.com/photos/[email protected]/5683294429/sizes/l/in/photostream/

8 Responses

  1. my company is stating that during lightning warnings from our ACCU-WEATHER ALERTS that as long as we are not exposed to the possible lightning strike meaning on the upeer 2 levels of our steel structure that we can go to work and feel completely safe in doing so. Is this true in what they are telling us? I am an electrician and I am not completely statisfied about that statement just because of the steel structure being a very good conductor for electricity. we are having a great big debate in this issue can you please respond soon we are just getting into our thunder storm season here in the United States Midwest part of the country Chicago, Illinois.

  2. Buddhika

    If we use structural steel (Column re bar ) for LPS ( lightning protection systems), will it heat up during lighting earthing. Is this cause to damage the Concrete column? Or else are there any side effects of using structural column (Reinforcement bars inside the concrete column) as part of LPS?
    Thank you.

  3. Zuraidah Idris

    Hi,

    With regards to using rebars in concrete columns as downconductors, I would like to refer to Table 5 in BS EN 62305-3:2006 which recommends that the material used should be hot galvanised steel. Is this a “MUST” because I understand that most rebars for construction are normal high tensile steel and not galvanised.

    I would appreciate it if you could give some clarification about this.

    Thank you.

    Zuraidah

    1. Hi Zuraidah,

      We really don’t have much experience in this particular aspect of the 62305 standard, and don’t know why Table 5 would specify galvanized steel. We agree with you that it is uncommon to see galvanized steel in use for concrete rebar. As far as we are concerned any bare steel is just fine as long as there is a continuous and positively bonded metallic path all the way to earth, and the overall impedance falls within the guidelines. What would be very bad is if you used a plastic coated rebar, then you could not use the steel as a down conductor.

      But that said, our official policy is to use copper down conductors for your lightning protection systems (LPS). The goal of the LPS is to protect the building and its super structure from lightning damage. Making the structural system of your building part of the LPS, may be cost effective, but it adds risk, potential damage, and electrical interference to sensitive equipment inside the structure.

      Hope this helps and sorry for the delay.

      1. alan m dransfield

        Hi Zuraidah
        I agree with you about using the structural steel and it might be OKf or a warehouse or farm but is is not suitable for a public building or a school.One other MAJOR violation is the failure to execute any Equipotential Bonding on these buildings.

Leave a Reply