Sand can turn from castle to trap

'I just couldn't believe it could happen'

Mark Mullaney here is playfully buried in the sand. On one occasion, it almost cost him his life.

(CNN) -- Like many families, the Mullaneys enjoy summer vacations at the beach.

And like most parents, Paul and Nancy are on high alert while their kids are in the water. They concede, however, that they let their guard down a bit once their kids are on land.

After all, what could go wrong when you're building sand castles?

Mark Mullaney found out something could go terribly wrong even on dry land.

"Me and my brother were digging holes and I was getting buried feet-first and we were jumping in butt-first," says young Mullaney.

"I got up and just saw two legs out of the sand," says his father, Paul. "The walls had collapsed on him and that's all you saw were two legs. And -- in trying to dig him out by my hands, not knowing what to do or how to react to the situation -- those legs slowly just kept slowing down."

Lifeguards managed to dig Mark out by creating a vacuum with a nearby trash can.

He'd been buried for about 10 minutes according to witnesses. Doctors say irreversible brain damage can occur after just three to five minutes. It took the work of paramedics performing CPR and doctors at a Boston hospital before he was OK.

That was three years ago.

"I just couldn't believe it could happen, basically because they were just playing in the sand and it was right in front of us," says Nancy.

Mark was victim of what's called a sand trap or sand hole.

"People who are in a recreational environment such as on the beach may be focusing their attention on other safety hazards -- most prominently water safety and drowning -- (and) may be unaware of the hidden risks associated with digging holes in the beach," says Dr. Bradley Maron of Brown University.

No one officially tracks sand hole incidents. But Maron gathered national media reports from the last five years and found an astonishing death rate of 61 percent for people trapped in sand.

Compare this to highly publicized shark attacks. Worldwide statistics indicate a 15-percent death rate during the last six years.

Maron wants to see sand hole accidents tracked and suggests posting warning signs on beaches.

Here are some things parents can do to ensure this doesn't happen to their kids.

The Mullaneys still go the beach. But young Mark does things differently now. "I don't dig that deep of holes and I don't get buried," he says.

Good advice for anyone on dry land.