BEVERLY - Landmark School employees felt firsthand the power of a lightning strike yesterday when they were knocked from their chairs by a shock wave of superheated air, fire officials said.

The strike occurred at about 4:30 p.m. as a small but fierce thunderstorm zapped Beverly but left nearby cities and towns mostly unscathed.

Beverly Deputy fire Chief William Walsh said the strike came within 50 feet of the employees who were in the school's computer building on Hale Street.

Walsh said the employees were watching the storm out the window when lightning struck two pine trees behind the building.

"It was probably the biggest destruction to a tree I've seen," Walsh said.

Trees struck by lightning usually have burn marks and are split in half, but these pine trees were shattered, Walsh said.

What's more, the workers who were watching the storm out the window were knocked off their chairs and onto the ground when the trees were hit.

"The air expands so rapidly when a strike (occurs) because of the heat and high moisture in the air," Walsh said.

The phenomenon is what's behind thunder, but when lightning strikes nearby, the resulting shock wave, or pressure wave, can be strong enough to knock a person down.

Walsh said the employees were not injured.

Former Salem State College professor and meteorologist Arthur Francis said the strike at Landmark School is the first case he's heard of someone being knocked to the ground from a lightning strike.

The same lightning strike at the private school for students with language-based disabilities proceeded to travel underground and hit another school building on the Beverly Farms campus.

"We assessed the building, and we did find smoke in the gymnasium," Walsh said.

Firefighters ripped out some wall board and found some charred marks on the wall.

Some faculty and staff were inside the building, but no one there was injured, Walsh said.

The same lightning also caused a fire alarm activation at Endicott College less than a mile down the road. Additionally, firefighters scrambled to locations across the city - from a home on Dodge Street in North Beverly to the School for the Deaf on Echo Avenue.

National Grid spokeswoman Elise Del Barone said 25 Beverly customers lost power during the storm and crews were working to restore power.

Neighboring cities and towns reported only minor damage, if any at all, from the storm.