'When thunder roars, go indoors' applies to everyone - even the White House sentry

WASHINGTON -- No matter what you're doing outside, lightning can be dangerous -- even if you're protecting one of America's most important buildings.

Video from a C-SPAN camera captured the moment a lightning bolt struck near the White House grounds Thursday as a Marine sentry stood guard.

DC lightning strikes outside of White House

Video from a C-SPAN camera captured the moment a lightning bolt struck near the White House grounds.

Analysis of the clip showed just 12 frames of video between the lightning strike and the crack of thunder, which translates to 0.4 seconds.

Since the speed of sound is considerably slower than the near instantaneous speed of light, a general rule of thumb is a lightning strike is one mile away for each five second delay in hearing the thunder.

A 0.4 second delay translates to being only 0.08 miles from the lightning strike -- or about 400 feet!

One of the National Weather Service's main messages around lightning safety is "when thunder roars, go indoors," which is exactly what this Marine did moments later.

Though C-SPAN cameras found the White House Marine sentry was back at its post a short time later as the storm raged.