Normally there are very safe and well tested and the Crew could abord safely at any time. But there are of course exceptions like the Space Shuttle which didn't have a Launch escape system. But of course, there are exceptions like the ejection seats of the Gemini program. There were tested as much as NASA would probably do with anything but there were tested in a 70% Nitrogen, 30% Oxygen environment and the Final Gemini capsule used a 100% Oxygen. So an abort would have likely set the Crew on Fire and burned them to death before they could land safely.

Normally there are very safe and well tested and the Crew could abord safely at any time. But there are of course exceptions like the Space Shuttle which didn't have a Launch escape system. But of course, there are exceptions like the ejection seats of the Gemini program. There were tested as much as NASA would probably do with anything but there were tested in a 70% Nitrogen, 30% Oxygen environment and the Final Gemini capsule used a 100% Oxygen. So an abort would have likely set the Crew on Fire and burned them to death before they could land safely.

EDIT: Sorry totally forgot the source. I think that Everyday Astronaut put it pretty nicely together in this Video