This article was posted 11/30/-0001 and is most likely outdated.

Vehicle Lightning Safety - Sun Roof
 

 
Topic - Lightning and Surge Protection
Subject - Vehicle Lightning Safety - Sun Roof

August 28, 2006  

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Vehicle Lightning Safety - Sun Roof

 

Question: I'm shopping for a new car and the model I'm interested in has a glass sun roof. Until now I thought that would not matter in regards of lightning safety because the rest of the body is metal, but I found a news report where a woman’s car windshield was hit by lightning. I never thought lightning could hit a car window. Is this possible?

 

Just out of curiosity, there's a substantial amount of Corvettes on the road, so it might be interesting to compare those cars in regards of lightning safety to metal cars. Did anyone ever get killed by a lightning strike while driving or seeking shelter in a Corvette?

 

Comment from Mike Holt: (Sorry the news report link is no longer online, but you can still get the picture)

 

Response: Safety against electric shocks, regardless of whether the source is lightning or man-made electricity, rests on creating an equipotential zone which encompasses all the points that are likely to be touched by any part of the person's body.  In case of vehicles, the metallic/conducting body of the vehicle forms an equipotential zone, thus keeping the occupants safe.

 

As an additional precaution, occupants are urged not to stick their arms out of the windows nor rest against the metallic sides of the vehicle through which the lightning current will be flowing.

 

The above protection is unaffected by whether the vehicle is insulated from the ground by means of rubber tires, or is in contact with the ground as in the case of trams and trains which have metallic wheels.  Hence, the statement in the news article that "the rubber tires saved the life of the motorist" is false and should be ignored.

 

A lightning strike to a vehicle can terminate on any point of its upward facing surfaces or on the radio antenna, with the antenna receiving a significant percentage of all strokes.  However, the probability that the stroke will terminate on any of the glass surfaces is very small.  In the reported case, there does not appear to be any deployed antenna and the stroke appears to have terminated on the tip of the metallic wiper on the passenger side of the windshield.  The resulting localized heating then shattered the windshield.

 

The risk of shattering of the glass of the car is outside the scope of the protection afforded by the equipotential rule.  This applies regardless of whether the damage is caused by a stone or by the heating from a lightning stroke.  However, based on typical configurations, the shattering of the windshield is not likely to compromise integrity of the equipotential zone. This is evident in this case as no electric shock was reported and the driver was able to steer the car to the side of the road.

 

The above applies both to windshields and sun roofs.  In other words, a sun roof will have negligible impact on lightning safety.  The undesirability of sun roofs rather rests on risk of rain leakage as the car ages and on weakening the frame, thus making it less safe in case the car overturns.

 

Abdul M. Mousa, Ph.D., P. Eng., Fellow IEEE Co-moderator

 

Correspondence obtained from the Lightning Protection forum on yahoogroups.com which discusses Lightning and Power Quality issues.

Visit this forum here:

http://groups.yahoo.com/group/LightningProtection

 

 

 
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Comments

  • Just so the issue is put into perspective, I think it should be noted that the likelihood of an occupied vehicle being struck by lightning is very, very low. Perhaps so low that it would not need to be a consideration when purchasing a vehicle.

    I would imagine the number of vehicles with a sunroof or convertible top involved in a roll-over crash is quite higher than those struck by lightning each year.

    Bryan Holland
    Reply to this comment

  • Mike Recently the company I work for established a metal galvanized chain link fence in front of a metal structure that has a 480V 100 amp disconnect mounted on it for a dust collector. The fence is only 27" away from the disconnect which is in violation of the NEC 110.26 and it's tables. The compant states that it will install a mangate thus when personnel work on the disconnect tyhe gate will be open. Problem I have with this is the gate is always locked due to security reasons, that is why the fence has been installed. I still feel the installation will be in violation of the NEC. Am I right in my thinking? Thank You, Mr Fetch

    Ken Fetch
    Reply to this comment

  • A good friend of mine was struck by lightning through the METAL roof of his Buick while driving on an isolated section of interstate highway. Between the electrical damage, and the damage that occurred when all four tires blew and the car spun off the road into a ditch, his car was a total loss. There were a dozen spots in the roof where the lightning burned holes through the metal and the melted headliner. He had second-degree burns on his head and on each hand where the current jumped to the steel-cored steering wheel.

    Fortunately, other than the burns and temporary memory loss (about two months of "Did I ever tell you the joke about . . .") he was fine.

    My point is, lightning that can go from the ground to a cloud can and does go wherever it wants. In my friend's case, a sunroof of glass MIGHT have caused the strike to occur somewhere other than direcly over his head.

    Mikey Meredith
    Reply to this comment

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