i think it was sulfur dioxide that was the culprit in those deaths, and the einstein-szilard refrigerator was also an ammonia-absorption refrigerator, though it didn't have leak-prone moving seals https://en.wikipedia.org/wiki/Einstein_refrigerator

ammonia-absorption refrigerators of more or less the einstein-szilard type still aren't leak-proof, even without moving seals as you will easily learn if you go to a junkyard to find spare parts for one (they're still popular in rvs, and i stayed in a hotel room earlier this year that had one, manufactured within the last decade)

freon was a huge safety improvement over early vapor-compression refrigerants like propane and sulfur dioxide, but ammonia-absorption refrigerators are a different beast entirely