From a lifeguard's chair here on the long, crowded beach, there are two ways to spot a neck injury in the making.

One is right in front: the waves. When they come in big, and break with a big slap right on the sand, there's a chance that a swimmer or boogie-boarder could come smashing down with them.

The other sign comes from behind the chair. Giddy teenagers, happy to have finally reached the beach, drop their stuff and pass the lifeguards at a dead run.

They dive straight into the waves -- unaware of an underwater sandbar until they hit it headfirst. "Sometimes they're still in their jeans," said 1st Lt. Walter R. "Skip" Lee III of the Ocean City Beach Patrol.

Neck and spinal injuries affect approximately 1 in 50,000 visitors to Maryland and Delaware beaches each year, and usually the incidents are not serious, ranking behind riptides and lost children in the problems lifeguards must address, local statistics for the past two summers show.

But at times, the injuries can be devastating, as in the case of Joshua Basile, a Potomac teenager partially paralyzed last year while on his boogie board near Bethany Beach, Del. Basile, now 19, and his family have called on authorities to provide more signs and warnings about a phenomenon known as "shorebreak," in which large waves that normally would break in deep water roll up and crash right onto the sand.

One town already has reacted.

After Basile's injury and recovery were chronicled in a Washington Post article July 4, Bethany Beach officials began discussions about increasing their warnings to beachgoers, said town Beach Patrol Capt. Joe Donnelly.

Many lifeguards, though, said the problem is difficult to handle, because the source of the injuries is often the same one that draws tourists to the beach in the first place: the crashing Atlantic surf.

"It's kind of like riding a roller coaster," said Todd Fritchman, captain of the Dewey Beach Patrol, of entering the water at the beach. "There's always that chance."

A steep incline at the Delaware and Maryland beaches can exacerbate the shorebreak problem. These strong waves can overwhelm swimmers standing in the surf, or boogie-boarders riding a wave, said Stephen P. Leatherman, a professor and beach-safety expert at Florida International University.

"It actually picks you up off the bottom and drives you like a pile driver into the beach headfirst," Leatherman said.

Lifeguards and some beach-safety experts said these conditions are made worse by beach-replenishment projects, which bring in sand from the ocean floor to replace parts of the beach that have eroded.

But Maryland and Delaware state officials said they take care to prevent making long-term changes to the beach. And statistics from a variety of sources suggest that Ocean City and the Delaware beaches are not significantly worse than beaches in Virginia and North Carolina when it comes to surf and spinal injuries.

B. Chris Brewster, president of the U.S. Lifesaving Association, said the most dangerous beaches in the country are in Hawaii and California, where the shore is constantly pummeled by big, breaking waves. Still, spinal cord injuries are relatively uncommon. For every spinal-injury case, there might be 100 or more instances when lifeguards must save people from rip currents or drowning, Brewster said.

A survey of beach patrols yields an estimate that at least 80 people were hurt enough to cause lifeguards to respond in Delaware last year, and about 85 in Ocean City. Only a handful of those resulted in serious spinal damage. Most beachgoers wind up with minor, but still painful, injuries. Their cases are common in the logbook of incidents kept by the Dewey Beach Patrol.

"Slammed by wave and abrasion on side of body . . . dislocated shoulder . . . abrasion," read Fritchman, paging through the book.

Most large Delaware beaches seem to rely on such temporary warnings as signs or flags, which are displayed when surf conditions are dangerous.

At Dewey Beach -- where about 14 spinal injuries occurred last year, at least three of them fractures -- Fritchman said there were no plans to switch to permanent signs. One reason, he said, is fears about the economic impact if the signs drove beachgoers away.

"For a small fraction [of people injured], we don't want to scare the entire whole," Fritchman said.

Ocean City has permanent signs on the back of every lifeguard chair that warn of shorebreak, as well as rip currents, sunburn and other dangers.

But even there, one family has argued, the current warnings aren't enough.

Margaret Lill of Silver Spring said her husband, Robert E. Lill, 65, broke his neck and died last year while riding the waves in an inflatable raft off Ocean City.

Though no one saw how he was injured, Margaret Lill said she's convinced a wave slammed her husband to the bottom.

"They have to make people more aware," she said.

Jacob Servin, 7, of Pennsylvania rides the waves in Ocean City, where 85 people were hurt badly enough last year to cause lifeguards to respond.First Lt. Walter R. "Skip" Lee III points out the warning signs on lifeguard chairs in Ocean City. Listed dangers include rip currents, "shorebreak" and shallow diving.Lifeguards in Dewey Beach, Del., begin their day with a briefing, then head to the beach for calisthenics before dispersing to their posts. "It's kind of like riding a roller coaster," Todd Fritchman, captain of the Dewey Beach Patrol, says of the ocean dangers. "There's always that chance."