An investigation has been launched into the shocking death of a crew member on the set of "The Lone Ranger."

A welder/water safety expert named Mike Bridger died on the L.A. movie set Friday while working inside a large water tank. Law enforcement sources tell TMZ it appeared Bridger suffered a heart attack.

Now Cal/ Osha, a workplace safety enforcement agency, has launched an investigation to see if there was any negligence or wrongdoing on the part of Bridger's employer, standard operating procedure following a death on a movie set.

Cal/Osha will look into how workers responded once they realized Bridger was unresponsive. Did they follow proper emergency protocol? Was there a proper emergency protocol?

A rep for Cal/Osha tells TMZ they are looking into the equipment and the tank and will also review the medical condition of the victim before his death. Cal/Osha will also conduct interviews with everyone who was on the set during the incident.

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There have been no official findings yet, and the final report could take up to six months to complete.

As TMZ previously reported, Bridger's friends and family believe he died of a heart attack and do not blame the film for his death.

Bridger had worked alongside "Lone ranger" producer Jerry Bruckheimer and star  Johnny Depp for years. One of his big breaks was working with Bruckheimer on the set of the first "Pirates of the Caribbean" movie.

Bruckheimer respected his work so much he hired him for every single "Pirates" sequel and then for "Lone Ranger." TMZ sources say he also became close with Depp while working on those films.

His funeral is currently being planned by family and friends.