HBO dealt with the Triangle fire — a 1911 tragedy that claimed the lives of 146 young women and teenage girls, caught in a high-rise factory that went up in flames — in its earlier documentary on the garment industry, “Schmatta: Rags to Riches to Rags.”

Now the channel revisits that part of the story in “Triangle: Remembering the Fire,” a 40-some-odd minute project from the same filmmakers — Marc Levin and Daphne Pinkerson — that premieres on March 21. (PBS’ “American Experience” aired its own take earlier this month.)

Triangle06 Although the question of the horrifying conditions that workers faced in the early 20th century — before organized labor fought for higher standards and protections — seems especially relevant right now, HBO’s interest in the material is more than just academic. Celia Gitlin, a 17-year-old Russian immigrant who perished in the fire, is the great aunt of the channel’s documentary guru, Sheila Nevins.

Given the clout that she wields within the documentary community, Nevins’ interest in labor issues, economic disparity, workplace conditions and the environment — as evidenced by themes in documentaries that HBO has championed — provides perhaps the strongest media foothold that labor has going for it at this tenuous moment. “Schmatta,” notably, chronicled the exodus of garment-industry jobs to cheaper locales, including Bangladesh, where another sweatshop fire with eerie parallels to the Triangle disaster occurred.

By contrast, “Triangle” is more personal than that and seeks to give those who died a dignified memorial — but still makes a strong advocacy case that resonates beyond what happened a century ago.

“People forget the Triangle fire at their peril,” Adelphi University historian Leigh Benin says in the film. “If people want to know what deregulated industry would look like, look at the bodies on the sidewalk outside the Triangle building.”

Subtle? No. Effective? Definitely.