An Iranian tanker, Sanchi, carrying 134,000 tonnes of cargo collided with the Chinese bulk, CF Crystal, on Saturday, in the East China Sea off Singapore. Sanchi’s crew of 32 were killed or are missing in the resulting fire. There has been considerable concern that the burning tanker might explode, spilling close to a million barrels of oil into the sea.

The reason for the concern is that the cargo carried aboard the tanker is not typical crude oil. The cargo is called condensate, which is a liquid, usually a byproduct of natural gas production, formed by a variety of gases which condense when extracted. Unlike crude oil, the liquid is often clear and odorless. Condensate is usually composed of propane, butane, pentane or hexane but can also contain carbon dioxide, hydrogen sulfide, aromatics and naphthenes, known as impurities.

Often referred to as ultra-light crude, it is far more flammable and explosive than most crude oils. China’s transport ministry said heavy winds, rain and high waves continued to hamper efforts to contain the fire on the Sanchi. Experts at the scene believed that, given the wave conditions, no more than 1% of the condensate was on the surface of the water.

What will happen if the ship sinks or explodes? Condensate spills are considered dangerous because of the toxicity of the chemicals involved. The condensate spill which could result from the sinking of the Sanchi would be, by volume, over twice as large as the spill caused by the Exxon Valdez in Prince William Sound in 1989. Unlike the Exxon Valdez spill, which was of heavy crude oil, however, the condensate dissipates and breaks down more easily than heavier oils.