Cave diving is like skating on a freshly frozen pond. You don't realize you're in trouble until the ice cracks.Wednesday's tragic deaths of a father and son at a cave system in Hernando County had a familiar ring. Two untrained divers ventured someplace they had no business going and died.The scenario has played out hundreds of times before, and unfortunately, will likely play out again. The father, Darrin Spivey, was a certified scuba diver, but he had no cave training.Learning to scuba dive is sort of like getting a driver's license. Sure, you can get behind the wheel of a car, but that doesn't mean you're ready to race in the St. Petersburg Grand Prix.No amount of open-water scuba diving experience can prepare divers for the hazards they will encounter inside a cave. The most obvious danger is a ceiling of rock.If a scuba diver encounters a problem 30 feet down in the ocean, he can surface. But cave divers don't have that luxury.Cave divers also must contend with darkness. On land, the night often can be scary and at times dangerous. But underwater, with a ceiling overhead, darkness can be deadly.Silt, fine particles of sand, mud or clay that coat most cave or cavern floors, easily can be stirred up by an errant flipper and render the most expensive diving light useless in a matter of seconds.To date, more than 400 people have died diving in caves. Fatalities peaked in the mid '70s, but the numbers began to drop after formal cave training became widely available. The National Speleological Society's Cave Diving Section (NSS-CDS) offers a four-stage training program.Back in the early '90s, I spent several years going through classes and diving under the supervision of certified instructors in order to write a series of stories about Florida's underwater caves.I learned that cave divers must carry nearly twice the amount of equipment as normal divers — two tanks, safety lines, lights and computers — backup systems for backup systems. In a cave, you can't count on anybody but yourself.I also learned that entering a cave is like running the Daytona 500. You might be fine for 499 laps — but lose focus for a second, and you won't make it to the finish line.Many open-water divers are drawn to caves because they've heard the tales of gin-clear water and massive caverns with white limestone walls. Most take the time to get the proper training before they hit the water.Those who don't take the time to get formally trained sometimes die. In fact, more than 95 percent of all cave diving deaths involve untrained divers. The remaining 5 percent are trained divers who go deeper than they should.Cave diving is time- and equipment intensive. It's not a casual sport, and there's no room for weekend warriors.My instructor once offered me some advice that I remember to this day. "There are old cave divers, and there are bold cave divers," he said. "But there are no old, bold cave divers."