In a big wave wipeout, a breaking wave can push surfers down 20 to 50 (6.2 m to 15.5 m) feet below the surface. Once they stop spinning around, they have to quickly regain their equilibrium and figure out which way is up. They may have less than 20 seconds to get to the surface for a breath of air before the next wave hits them. Additionally, the water pressure at a depth of 20-50 feet can be strong enough to rupture one's eardrums. Strong currents and water action at those depths can also slam a surfer into a reef or even the floor, which can result in severe injuries or even death.
One of the greatest dangers is the risk of being held down by two or more consecutive waves without the chance to reach the surface for air. Surviving a triple hold-down is extremely difficult which is why it is important to know how to swim out of these situations.
Despite these hazards, very few big-wave surfers have ever died in the practice of the sport, with the notable exceptions of Mark Foo, who died surfing Mavericks on December 23rd, 1994, Donnie Solomon, who died exactly a year later at Waimea Bay, and Todd Chesser who died at Alligator Rock on the North Shore of Oahu on February 14th, 1997. A possible explanation for the relatively low fatality rate is experience; most big-wave surfers are highly skilled in the water and have likely trained themselves to handle the difficult conditions.