Space debris is accumulating in earth's orbit, which is a problem because, "due to its very high speed in orbit—even relatively small pieces can damage or destroy satellites in a collision."

As an example, Russia's November 2021 anti-satellite test created over a thousand pieces of debris, a cloud of which came close to the International Space Station, "forcing astronauts to take shelter for hours in a pair of spacecraft capable of returning them to Earth" according to the New York Times.

Evasive manoeuvres can help, but according to NASA, we can track discrete objects >5cm, but debris shields are effective only for objects <1cm. This means there are objects between 1 cm and 5cm that can severely damage human spacecraft, but cannot be tracked.

Space debris could kill humans in three ways. First, space debris could damage human spacecraft and kill one or more of its occupants. Second, re-entering space debris could kill humans on earth. Third, space debris could take out satellites linked to critical infrastructures and thereby cause death on earth via failure of such infrastructure. This question only focuses on the first risk — i.e. astronaut fatalities in space.