Star Trek: Enterprise, season 2
Shockwave
Summary
While visiting an alien mining colony on Paraagan II, a shuttle accidentally sets fire to the large amounts of tetrazine in the atmosphere, instantly incinerating the 3,600 colonists on the surface. Despite Lieutenant Reed's precautions, Captain Archer personally puts full blame on himself for all the deaths caused. He doesn't argue with Starfleet's Admiral Forrest when Enterprises mission is officially cancelled, and the ship is ordered to return home (on the advice of Vulcan Ambassador Soval).
Summary from Wikipedia, CC BY-SA 4.0.
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