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Mr. Vollmer said the problem occurred among 24 valves that control the flow of nitrogen tetroxide, a propellant used by Starliner’s thrusters.

Some of the nitrogen tetroxide appears to have permeated through Teflon seals and interacted with moisture on the other side to produce nitric acid, Mr. Vollmer said.

Orange clouds in the video might be toxic hydrazine and nitrogen tetroxide, which fuel the rocket’s first stage.

The elevated levels of nitrogen tetroxide around Crew Dragon reinforce the necessity of keeping the splashdown area clear throughout the recovery process, he added.

And levels of nitrogen tetroxide, a toxic oxidizer, remained slightly elevated around the capsule for longer than mission team members expected, spurring the recovery team to “purge” the gas before extracting Behnken and Hurley from the spacecraft.