The type of oil pouring from the container ship Rena is banned in some southern seas because of the problems it causes in cold water, an expert says.
The leaking oil from the Rena has been identified as HFO (Heavy Fuel Oil) 380.
Heavy fuel oils are the heavy fractions of oil left after light fractions, such as jet fuel, kerosene, petrol and diesel, are removed from crude oil, according to John Pfahlert, executive officer of the Petroleum Exploration and Production Association of New Zealand (Pepanz).
These light fractions form a sheen on water but evaporate quickly. Heavy fuel oils react quite differently.
"Virtually all ships in the world use heavy fuel oil to power them because it's cheap and it's fairly abundant," Mr Pfahlert said. "The way they get it to run is that they have to have heaters in the fuel tanks and the flow lines to the engines to keep this stuff sufficiently fluid so that it can actually be pumped like a fuel and used in the engines.
"If it gets cold, it forms a gloopy substance exactly the same as the thing you are seeing on the beach."
There had recently been a ban on use of heavy fuel oil in ships plying Antarctic waters and in New Zealand's subantarctic Islands. "It's a recognition it's very, very difficult to clean up in the cold-water environments."
Bay of Plenty medical officer of health Phil Shoemack said the oil fumes were unlikely to cause any health problems, however some people might be affected by the smell.
"We don't believe it's enough to cause any damage. It's more of a nuisance," he said. "But it might be sufficient to cause problems for some people ..."By Jarrod Booker Email Jarrod