Instances wherein your life may hang in the balance abound. Such as atmospheric braking when landing on Mars? ;^)
Many terrestrial examples, but that one sprang to mind.
I recall an incident, but not the details of the incident, wherein a jet airliner was loaded out with fuel a number of years ago. This recollection may or may not be accurate in every detail, but as I recall, the people fueling the airliner were asked to load it with "liters" of fuel instead of gallons. Or perhaps it was kilos versus pounds. In any case, the error that they created was very large and the airliner ran out of fuel somewhere up in Canada, I believe. The pilot succeeded in landing the craft on a drags-strip which was in use at the time. Fortunately, some of the people using the strip saw the airliner making its approach and cleared the strip.
This is what I had in mind when I made my comment concerning one's life hanging in the balance. There are many cases where it is very important that people making technical decisions have a clear understanding of the relationships (or lack thereof) between the English measurement system and the Metric system or System International.