As the Miami firefighter cooked, he joked with Oscar Celorio, a man whose boat was anchored next to his, about trading some meat for some of Celorio's cakes.
But seconds later, Hernandez's day off turned into a rescue mission, as he jumped into the knee-high waters to retrieve and revive a man who had apparently dove into the shallow water from a nearby boat.
The impact knocked the 36-year-old man out.
''When I got him out, his forehead was purple and black, he hit himself so hard,'' Hernandez said. ``I suspected he had spinal injury and with his weight, his neck went way back.''
The victim -- whose name was not released -- is now recovering at Jackson Memorial Hospital.
No one, Hernandez said, saw him jump. Yet the fireman said he can still picture the man standing on the side of a boat.
''If I would have known he would have done that, I would have told him not to do it,'' Hernandez said. ``I feel so bad.''
Moments earlier, Hernandez said, the victim and his passengers were struggling to anchor their boat because of the choppy seas and wind that July 18.
So when Hernandez saw the man floating face down, he didn't think much of it at first, he said.
''He looked like he was looking for the anchor or something,'' Hernandez said. 'But then I said, `that guy is not moving, that guy is knocked out.' ''
So Hernandez abandoned the barbecue and let his training and instinct take over.
Seconds after the victim regained consciousness and told his savior he couldn't feel his arms or legs, Hernandez directed a nearby boater to call rangers at Biscayne National Park.
In the meantime, Hernandez said he asked his friend, Luis Carraquillo -- a Miami fire rescue paramedic, too -- to help him hold the man and make sure his neck and spine wouldn't be further injured.
Following Hernandez's orders, other boaters jumped in the water, said Celorio -- who witnessed the entire rescue -- and used their bodies to block the incoming waves and help keep the man still.
Hernandez ''was very professional,'' Celorio said. ``He was giving the victim first aid, and was directing everybody.''
Within minutes, Hernandez said, rangers arrived with a backboard and a neck-brace. And while Hernandez was tending to the victim, ranger Jason Marsh was coordinating with Miami-Dade fire rescue to arrange an air lift.
Celorio said, although he was worried about the man's condition, what struck him most was Hernandez's reaction.
''What impressed me was that Hernandez was on his day off,'' Celorio said. ``And his priority at that moment was the injured person -- nothing else.''
