Safety Orange vs Fire Orange

How close are they?

ΔE 17.4, loose: different enough that you should pick on purpose. Fire Orange is noticeably darker, cooler than Safety Orange.

Can I use Fire Orange instead of Safety Orange?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Fire Orange is noticeably darker, cooler than Safety Orange.

Can I use Safety Orange instead of Fire Orange?

The same difference applies the other way round: Safety Orange is noticeably lighter, warmer.

ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.