The fire engulfing an Iranian tanker off China is being fueled by the oil on board, a scenario seen reducing the amount of supply that may spill into the sea and cause widespread environmental damage.

The Sanchi was ferrying 1 million barrels of condensate—a highly flammable hydrocarbon liquid that’s used in petrochemical production—when it collided with a Chinese cargo carrier on Saturday, leaving the Iranian vessel’s 32 crew members missing or dead. The tanker is still ablaze and its cargo is what’s keeping it burning, according to South Korea’s Coast Guard, which is involved in search and rescue operations.

The oil tanker ’Sanchi’ on fire after a collision on Jan. 7. Source: South Korea Coast Guard/EPA
The oil tanker ’Sanchi’ on fire after a collision on Jan. 7. Source: South Korea Coast Guard/EPA

Condensate is more flammable than crude oil or fuel, and a portion of it will be burnt off rather than spilled into the sea, a Korean Coast Guard official said on Tuesday, adding that it’s watching for any possible environmental damage. “Clarification on how much has burnt and how much has leaked is needed,” Rashid Kang, campaigner at Greenpeace East Asia said in an emailed statement. “If a large amount of the condensate oil has leaked into the water, there could be an impact on local fish stocks and marine life. However, with the tanker currently on fire, it is expected that a lot of the oil will be burnt up or evaporate under the high temperature.”

While the condensate is flaming, the gases released are highly toxic, meaning rescue personnel can’t operate easily near the vessel, according to China’s Ministry of Transport. Weather and water conditions in the area are also hurdles, with rain, winds and tall waves, it said in a statement.

Complicated Clean-Up

“If the ship sinks before all the condensate has burnt off or evaporated, the clean up efforts will become considerably more complicated,” Greenpeace’s Kang said. The East China Sea is a large fishing area, and species such as mackerel could be affected, it said. If there were a large-scale spill, then species such as the small yellow croaker and hairtail could be affected through the food chain, according to the environmental group.

If all the condensate leaked into the sea instead of burning off, the spill would be one of the biggest from a ship over the past five decades. The cargo size of about 150,000 metric tons aboard the Sanchi exceeds the 35,000 tons of crude that the Exxon Valdez spilled near Alaska—the biggest such incident in U.S. history. That 1989 spill led to the destruction of thousands of marine fauna and long-term environmental damage.

Ship Collision

The Sanchi, which collided with bulk carrier CF Crystal about 160 nautical miles off the coast of Shanghai on Saturday, was at risk of exploding and sinking, as China, South Korea and the U.S. continue to search for the ships crew—30 Iranians and two Bangladeshis. The body of one sailor was recovered, according to the Coast Guard official.

Everyone aboard the CF Crystal, a Hong Kong-registered cargo vessel that was carrying grain from the U.S. to China, were rescued, according to China’s Ministry of Transport. The Sanchi’s cargo was worth about $60 million, according to a spokesman for Hanwha Total Petrochemical Co., which was the buyer of the condensate.

Hanwha, which on Monday bought five cargoes of naphtha—another feedstock used in petrochemical production—for February, is said to be checking the availability of the fuel for January delivery after the tanker incident.