Fear of the inky black void at the bottom of the sea and of drowning down there drives the simple but flawlessly executed diver-down thriller “Last Breath.”

It’s an almost-real-time account of a deep sea diving accident, and a film — like “Sully” or “Only the Brave” — that illuminates a little-appreciated profession and the professionals who practice it.

Director and co-writer Alex Parkinson based this film on a documentary he made on the same subject with the same title of a few years back, putting the story in the capable hands of Woody Harrelson, Mark Bonnar, Cliff Curtis, Simu Liu and others and underwater cameraman Ian Seabrook, who give us a tense, workmanlike look into one of the world’s most dangerous professions in one of the most forbidding environments on Earth — hundreds of feet underwater.

“Saturation” divers spend month-long shifts doing maintenance on North Sea oil pipelines and rigs, living and sleeping in pressure chambers, diving for hours at a time to prevent leaks and fix gear in the pitch-dark of the sea bed.

Harrelson plays Duncan, the old salt and veteran of the trade whose 20 year career is winding down. “Peaky Blinders” vet Finn Cole is Chris, Duncan’s young Scots protege with a new seaside Aberdeenshire manufactured home and a fiance (Bobby Rainsbury) to come home to.

Simu Liu is Dave, a “legend” of the profession, “The Vulcan,” they call him. And Cliff Curtis is the new skipper of the Tharos, the support ship that gets divers to and from “the worksite,” and which hovers over that site — in all sorts of sea conditions — when it sends them below.

That “hovering” is what goes wrong one night during a storm. The thrusters that maintain station for the Tharos quit, divers are trapped below and there’s only so much time to save them.

This “true story” sets up like a veritable primer on perilous workplace melodramas of the “Backdraft” or “The Perfect Storm” model. The characters are “types” — the guy with the gal he promises to come home to, the crusty veteran being put out to pasture who regales one and all with his “in MY day” claims about all you used to need to do this deadly work was “a little common sense and a bottle of Scotch.” Throw in the perhaps untested captain, the all-business diving veteran you can supposedly rely on and the improvising crew who scramble to save the day before the oxygen runs out and you’ve covered all the formula melodrama bases.

Parkinson knowing this story backwards and forwards means he’s become an expert on how to tease out the suspense and tug at the heartstrings with this material.

And that is the oxygen that “Last Breath” lives on — a “routine” day on the job that is anything but, an outcome which we fear will be the worst and the people trained to handle the situation thinking outside the box, and whatever their emotions, never panicking, keeping calm and carrying on.

Rating: PG-13, profanity, life-and-death peril

Cast Woody Harrelson, Finn Cole, Bobby Rainsbury, Mark Bonnar, MyAnna Buring, Kosph Altin, Cliff Curtis and Simu Liu.

Credits: Directed by Alex Parkinson, scripted by Richard LaFortune, Alex Parkinson and David Brooks. A Focus Features release.

Running time: 1:33