No it is redundant. The comparative and superlative of "safe" are "safer" and "safest". The "most" is unneccesary. You would write or say simply "the safest".
The safest and easiest way to check petrol purity is the filter paper test. Take a piece of filter paper and drop a small bit of petrol on it. If it evaporates in a short amount of time and doesn't leave a line or mark behind it is good quality.
That is the correct spelling of the adjective "safest" (most safe or secure).
Petrol is gasoline and most internal combustion engines, thus most vehicles, use it.
Petrol will catch fire first, petrol is highly flammable, diesel is not.
Petrol is mainly alkanes, and so is probably miscible with most of them.
petrol
a goldfish
Iceland
if petrol was in short supply then emergancy services would be the vehicle that needed it most eg the police, ambulance and fire brigade
The Cadillac beast is the world's most safest car with bomb proof body & bullet proof tyres & windows.
Most elements are completely stable and safe. However, the safest elements would be the most unreactive. So, in that sense, the Inert Gases (exc. Radon, which is radioactive) are probably the safest group of elements, as they are completely unreactive.