Until now the Baltic Sea has been relatively free of oil accidents. But its record may not stay so clean for long. Oil tanker traffic in the region has increased dramatically to around 20,000 tankers per year - many of which are quite large, said Bernt Stedt, a disaster expert with the Swedish Coast Guard.

Since traffic on the Baltic Sea is concentrated in just a few routes with many shallow and narrow passages, the risk grows that a large tanker could crash and cause a catastrophe.

At the end of August, experts coordinated an exercise called Balex Delta in which they simulated a Baltic oil disaster. Rather than using a real oil slick, which would have been far too risky for the environment, they distributed some peat on the water to get a rudimentary sense of an oil spill's magnitude.

Brushing oil away

The project's organizers worked with the followed scenario: Somewhere between Helsinki and Tallinn, a tanker collides with another ship. 15,000 tons of crude oil spill out and drift toward Finland's coast. A fleet of 50 special ships must then try to control the spill, imagined to be seven kilometers long (4.3 miles) and one kilometer wide.

A German ship dubbed the Arkona was among the vessels involved. The side of the Arkona houses two long, metal arms that can be extended and placed on the water surface to siphon away oil. This happens by way of rotating brushes attached to the arms, which bring the oil on board and then pump it into large tanks before bringing it back to land.

Other ships were assigned to set up oil barriers using kilometer-long rubber tubes filled with air. Their goal was to prevent the hypothetical oil slick from reaching the Finnish coast, dotted with numerous islands.

It takes quite heavy boats to pull the barriers apart and then put them in the right places, said Markku Rissanen, the chief fire officer in Helsinki's rescue department. Positioning the barriers can be a big problem when the wind changes, and the oil moves in a different direction.

Complex logistics

Rescue workers get support from researchers like Sakari Kuikka, who specializes in fisheries systems at the University of Helsinki. His team developed software that can predict how oil will spread out in water over a given number of hours or days and in specific weather conditions.

"We have been trying to locate which threatened species, populations and habitats can be protected by the oil barriers," Kuikka explained. If it's known, for instance, that a certain bay houses endangered species, then rescuers can be directed to block off that area first.

The greatest challenge in the Balex Delta exercise was coordinating all of the special ships and operators involved.

"During this exercise, we are trying to test the whole oil recovery chain, from the beginning to the shore line. That's a challenge because we have more than 500 people here, nearly 30 ships, two helicopters and more than 10 different departments," Markku Rissanen noted.

Deceptively good weather

To coordinate the maneuver, a central station was set up on one of the ships to serve as a control point. In general, the exercise went according to plan, partly thanks to good visibility and calm waters during the exercise. These would be ideal conditions for containing an oil spill. However, a collision or other disaster often takes place during periods of bad weather, which can really push rescue operations to the limit, said coast guard expert Bernt Stedt.

Even the highest-performance ships used in the exercise can operate only at wave heights of up to two and a half meters. Severe storms can create waves that are much higher. In harsher conditions, Stedt said, rescue workers know they'll just have to wait.