Use with abandon.
Disclaimer: FAWPI seems to me to be exponential.
As you saunter past the 10 hours that make up your shift,
and then swing over the 12.5 hour safety break,
you then arrive somewhat saggily at 17 hours of wakefulness and descend
until you crash and burn at the 24 hour mark.
The last 7 hours of wakefulness doubles your Performance Equivalent
of a Blood Alcohol Reading from 0.05 to 1.0.
Sounds exponential to me.