- The Halachah says (Rambam Rotzeach-uShmirat-Nefesh 11,5, read on to ch.13, interestingly haMechaber omitted those Halochos):
"הרבה דברים אסרו חכמים מפני שיש בהם סכנת נפשות.:"
"Our Sages forbade many matters because they involve a threat to life."
It is clear from Rambam, that our Sages of the Talmud defined "things that he considered dangerous" based both on their Torah AND empirical knowledge. Rambam followed the principle and added additional warnings based on his personal experience as a practicing physician and common knowledge of that time.
The Poskim of our times, used the same approach when discussing the dangers of the 20th century (such as smoking), with some (Chofetz Chaim, Thitz Eliezer) clearly prohibiting it and some (R' Ovadia Yosef and R' Moshe Feinstein) finding ways to allow. They consulted the leading professionals to get an אמדנא of the danger.
I heard a Shiur by a Rabbi in Jerusalem, that suggested, that since we all as a society (אנן סהדי) appoint special people responsible for setting the official definitions of "life threating" and not "life threating" situations in numerous areas, such as traffic laws, medicine, construction safety and many more, those laws can constitute the bar (אמדנא) for the Mitzvah of ונשמרתם.
Did some of the Poskim mention in their Shu"Ts relying on the federal laws and regulations (such as FDA for example), and do such directives create obligating אמנדא for שמירת הנםש Mitzvos?