Turns out 250 tons of riveted, reinforced steel doesn’t stand a chance against 6 pounds of copper-encased explosives.

The directional charges — all 36 of them, essentially C-4 plastic explosive encased in copper — sliced through the steel supports for a 251-foot section of original Kansas River bridge along the Kansas Turnpike, dropping the 55-year-old hunk of history onto a temporary sandbar about 30 feet below.

It’s a process that will be repeated at 10 a.m. Thursday, when a similar hunk is scheduled to be blasted, and then again in early December as contractors for Kansas Turnpike Authority continue to dismantle the original bridges that were built beginning in 1954.

“This went great,” said Rex Fleming, the turnpike’s project engineer. “We’re ready to do it again.”

Jeremiah Seibel wouldn’t mind seeing it again. The 11-year-old took in Sunday’s blast from the safety of Burcham Park, standing tall alongside his 4-year-old brother, Jude, who had his hands over his ears the whole time.

“I’ve seen things blow up, but never up this close,” Jeremiah said confidently, moments after gasping as the bridge fell. “Usually it’s just firecrackers or something — blowing up a plastic cup with a firecracker.”

Not a bridge that used to carry two lanes of turnpike traffic since the day the highway opened in 1956.

This was better.

Lots better.

“It’s just bigger,” he said, cracking a wide-eyed smile. “I just knew it’d be awesome.”

Jeremiah, his brother and parents were among more than 150 people who crowded into Burcham Park, where a picnic shelter in the park and an awning at Kansas Athletics Inc.’s boathouse provided curious onlookers with all the cover they’d need from a steady rain that had threatened to delay the scheduled 12:30 p.m. blast.

In the end, the elements sped things up.

Anticipating a break in the weather, officials geared up to blast the bridge earlier. Shortly after noon, the Kansas Highway Patrol started slowing down traffic that had been approaching Lawrence from the east and west, just long enough to open up a window of no traffic on a new Kansas River bridge that now carries all turnpike traffic.

The countdown came to turnpike officials over hand-held radios — 5, 4, 3, 2, 1 — before onlookers saw the flash of magnesium in the last lines. Then the blasting caps and intense flash from the RDX explosives, which sent copper cutting through the steel supports at 26,800 feet per second.

The bridge section already had hit the ground by the time the explosion’s shock and sound had reached Burcham Park, where camera shutters struggled to keep up with the action.

Observers watched from under the shelter, leaning against trees and, for some affiliated with Kansas University’s crew team, atop the boathouse’s observation deck. A few Lawrence old-timers, such as Lawrence street division manager Tom Orzulak, mixed in with families from Wichita and Mulvane, some in town for the KU-Nebraska game Saturday afternoon.

Dr. Terry Riordan, a Lawrence pediatrician, had stopped by the park after making rounds at nearby Lawrence Memorial Hospital.

“I saw two new ones — two babies coming in — and one bridge going out,” he said.

The bridges are being demolished to make way for construction of a second new bridge over the river. The entire project is replacing the two original bridges, overhauling interchanges and making other upgrades at a cost of $130 million, and is to be completed by the end of 2011.