All oils cause pollution to the sea and for this reason MARPOL does not distinguish between a good oil and bad oil. Annex I of the MARPOL applies to all type of oils.
The concept of persistent and non persistent oils came into light during the cleaning efforts of major oil pollutions including that from Torrey Canyon.
It was then noted that pollution of few oils does not require any special clean up operation as these oils will
- either dissipate rapidly through evaporation, or
- the sheen would die down in the sea waves
This was the time when the focus was put in dividing the oils in two categories. And these were
- Persistent oils and
- Non-persitent oils
It is all in the names. Persistent oils are the one that persists and do not dissipate easily.
But persistent oils still needed a definition on the basis of which the oils can be categorised into persistant or non persistant.
After much research and study, the IOPC fund adopted definition of non-persistent oils which is
“non-persistent oil is oil which, at the time of shipment, consists of hydrocarbon fractions,
- at least 50% of which, by volume, distils at a temperature of 340°C (645°F) and
- at least 95% of which, by volume, distils at a temperature of 370°C (700°F);
when tested by the ASTM Method D86/78 or any subsequent revision thereof”.