Close friends tell TMZ the victim's name is Mike Bridger -- a welder and water safety guy who had 20 plus years in the biz ... and one of his biggest breaks was working with Bruckheimer on the set of the first "Pirates of the Caribbean" movie.
We're told Bruckheimer respected his work so much ... he hired him for every single "Pirates" sequel and then for "Lone Ranger." Our sources say he also became close with Depp while working on those films.
Close friends of Mike tell TMZ ... the family does not blame the production company for his death, and believes he died of a heart attack.
TMZ broke the story, Mike was working in a large tank on "The Lone Ranger" set when he passed away. Law enforcement also believe his death was due to a heart attack. He was 48.
His funeral is currently being planned by family and friends.