QUESTION #101

# Can lightening travel through matter (specifically a canvas awning supported by aluminum poles) and strike the children sitting beneath on wooden tables supported by a concrete slab? If so, how do you calculate a safe distance from the lightening that is visible?

Lightening is a discharge of static electricity that 'contains' millions of volts of potential difference and many thousands of amps of electrical current. The temperature of a lightening bolt is hotter than the sun by at least 15 times! So, to put it plainly, a lightening bolt can pretty much travel through anything it wants! This is like asking 'Where does a 300 pound gorilla sit?' 'Anywhere it pleases!'

Now, why would lightening go one place and not another? Would lightening 'go after children sitting on a concrete slab?' Probably not. Lightening will travel the path of least resistance from cloud to ground or ground to cloud. But this is resistance to electrical current flow. So, can the lightening 'more easily' ground itself on bare ground or through concrete? Most often bare ground offers less electrical resistance so a concrete slab is probably safe. But, if that slab has steel reinforcement bars in it and if these pairs are exposed that slab would most certainly not be safe. You car is safe because the rubber, real or not, offers a lot more electrical resistance to the lightening than the bare ground.

As to what is the safe distance from visible lightening that depends on where you are relative to the storm and which direction the storm is moving and how fast it is moving and how big it is or is getting. With all these factors to consider, and I am sure to have left many out, the safest thing to do when you see a storm coming is to get inside a building or a car. If you cannot, I am sure you already know the drill.

Note by the editor: The most I am concerned with are those aluminum poles supporting the canvas awning. Since they are conductors, and they are probably placed directly into the ground they are a perfect attractive point for lightening.
Answered by: Tom Young, M.S., Science Teacher, Whitehouse High School, Texas