We are all aware of the Torah imperative to avoid even the smallest chance of danger regardless of the financial or physical cost or even if it involves the violation of a mitzvah.  Yet, we intuitively understand that the Torah allows us to drive in a car even though in 2006, 1.42 people died for every 100 million miles driven.¹  An analysis of some of the rationales for why this is permitted will help us understand how Poskim evaluate other less obvious situations to decide whether the Torah wants us to ignore or avoid a specific risk. 

Note:    The goal of this article is to present some factors involved in this type of decision, and the article is not intended to serve as a source for a halachic ruling.  Rulings on these types of questions must be addressed by a Posek.

There appear to be a number of possible reasons to permit an act that appears to have some element of risk:

1. Although the halacha requires that one be concerned with even a tiny chance of danger, there may be some risks that are so remote that we may ignore them even as they relate to sakanah.  An extreme example of this is that Chasam Sofer² says that (as relates to pikuach nefesh) one need not be concerned about occurrences which happen once in a thousand years.  Chasam Sofer’s guideline is obviously meant as a hyperbole, and the exact level at which something is considered truly remote as relates to sakanah requires further clarification.
2. In deciding whether an act meets the aforementioned criteria of being “too risky”, one must be careful to properly identify the “act”, as follows.  For example, while there is reason to believe that eating too much salt raises one’s blood pressure, eating too much pop leads to diabetes, and basking too much in the sun may lead to skin cancer, that doesn’t mean that it is forbidden to ever consume salt or sugar or walk outdoors.  In each of these cases, it is a dangerous “act” when one has more than a specific amount of the otherwise-safe item, and therefore one cannot classify salt as being dangerous and forbidden.³
3. Even when the item is considered truly dangerous, the Gemara⁴ tells us that if people commonly ignore the danger inherent in a specific act (דשו ביה רבים ), others are permitted to follow suit and rely on Hashem’s protection.  At the same time, as people become more concerned with that particular danger, the previously-permitted act may become forbidden.  A full discussion of this principle, known as שומר פתאים ה' , is beyond the scope of this article,⁵ but the following words of Rav Shlomo Zalman Auerbach⁶ are instructive:

ולענין עיקר הדבר מה נקרא ספק פקוח נפש ומה לא, ועד איפה הוא הגבול, גם אנכי בעניי הסתפקתי טובא בזה, אלא שמצד הסברא נלענ"ד דכל שדרך רוב בני אדם לברוח מזה כבורח מפני הסכנה הרי זה חשיב כספק פקוח נפש וקרינן ביה בכה"ג וחי בהם ולא שימות בהם, אבל אם אין רוב בני אדם נבהלים ומפחדים מזה אין זה חשיב סכנה, קצת דוגמא לכך הרכבת [זריקת] אבעבועות לילדים, אע"ג דמצד הדין אפשר שצריכים באמת להזדרז ולעשותו בהקדם האפשרי אם הרופא אומר שכבר הגיע הזמן לעשותו, אך אעפ"כ אין רגילין כלל לעשותן בבהילות ובזריזות, ולפיכך אף אם באמת יש בזה קצת סכנה הו"ל כמ"ש חז"ל והאידנא שומר פתאים ד' וחלילה לחלל שבת עבור כך, משא"כ אם אחד נמצא במקום כזה שיודע ברור שאם לא ירכיב עכשיו את האבעבועות בשבת יצטרך לחכות ד' או ה' שנים, כיון דבזמן מרובה כזה ודאי נבהלים ומפחדים לשהות, אפשר דשפיר חשיב כפקוח נפש ודוחה שבת.
Tzitz Eliezer⁷ adds two other factors to consider:

4. Binyan Tzion⁸ says that the stringency associated with sakanah only applies if the person is already ill or in some other situation which might lead to death, but doesn’t restrict a person from entering a situation where sakanah may develop in the future. 
5. Shem Aryeh⁹ understands that one may do those things which are required for “normal living” and need not be concerned with the sakanah aspect.  It is noteworthy that within this opinion, Tzitz Eliezer cites a disagreement as to whether it is limited to people entering the situation for business purposes or if it applies to all people.¹⁰   

Summary

There are many experiences in life which carry with them a certain element of risk but are permitted according to Halacha.  Using the example of food, we determine whether a specific food is “safe” based on a number of factors – what the chances are that consuming the food will lead to danger, how much of the food must be consumed before reaching the dangerous level, and whether consumption of such foods is considered safe by the average consumer.  [Later Acharonim suggest two other factors that may play a role in this decision].  Clearly the answer to this question will be different depending on how much of the given food the person is considering eating, and on what is considered safe in the locale and times that the person lives in.