It sadly was over so fast that I couldn't take a screenshot, but basically this is what happened:
One of my dupes was digging away at some sand that fell down and trapped him in a rather low oxygen environment. he was holding his breath. He got hungry and grabbed a worm that was nearby. Still in the low oxygen environment, holding his breath he was munching down on it, but for the duration of that eating animation he suddenly had an exo-suit helmet, which vanished after the animation finished.
Have dupe in low oxygen environment without suit (or sweater). If he gets hungry and starts eating still inside that environment, the helmet should appear.