Laboratory tests reveal no cause of museum explosion

Various explanations offered for rupture of gas line

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Laboratory tests have not revealed the exact cause of an explosion at the National Museum in Helsinki on Monday. Investigators at the Finnish crime laboratory say that tests on residue collected at the location of the blast have not shed any light on the exact composition of the gas that exploded in a cleaning closet in the museum.
      Police speculate that methane from the drainage system could have been ignited by a spark from a fuse box, and that the gas had accumulated there after the ventilation system broke down in the cold weather.
      Police are not sure how the methane got into the sewage system.
     
Antero Hakkarainen of Helsinki Water rejects the possibility that an explosive mixture of gas would have formed in the sewage system itself. He is certain that the blast is linked with a leak in a gas line that was detected nearby.
      The break in the gas line was near a number of underground pipes and cables. The cast iron gas pipe is near district cooling pipes, as well as water mains and electric cables. A sewage line runs on south of the gas line.
      The gas line, which was built in 1911, and a district cooling line dating back to 2004 inersect at Museokatu, where the gas leak was detected. The two pipes are separated by about half a metre of earth.
      Marko Riipinen, head of the district cooling unit of Helsinki Energy, does not believe that the cooling pipe could have caused the rupture in the gas main. He says that the line has no effect on the dampness or temperature of the surrounding earth.
      "I don’t see any connection. If something had broken during the work, it would have been noticed then. In Helsinki we know the locations of what can be found in the ground exceptionally well", Riipinen says.
     
Jarko Alanko, managing director of Suomen Kaasuenergia, which sells natural gas in the Helsinki region, sees a possible connection. He says that the old gas main lies in earth with a high clay and rock content, while the cooling lines are surrounded by sand. Alanko notes that the different types of earth freeze in different ways.
      Raimo Saarinen of the Public Works Department of the City of Helsinki says that differences in the composition of earth and soil are taken into consideration during road construction and repairs. He says that problems arise with old streets, which lack any recent comprehensive plan.
      The situation is made more difficult by the fact that many different institutions are involved in excavations. Cable television operators have their cables underground, Helsinki Energy has district heating and district cooling lines, and Helsinki Water has water, sewage, and rainwater pipes.
      "The more institutions are involved in the same trench, the closer cooperation should be. Whenever there is digging next to a pipe, there is always a risk of altering an old, stable structure." Saarinen points out.
     
At the National Museum, all silver objects have been moved away from the display area affected by Monday’s explosion. Researcher Raimo Fagerström says that about half of the objects were largely unscathed, about 20 percent sustained slight damage, and 20-25 percent were damaged more seriously.


Previously in HS International Edition:
  Possible connection between Museokatu gas leak and National Museum explosion under investigation (26.1.2006)
  Methane leak causes several evacuations in downtown Helsinki (25.1.2006)
  Violent explosion shakes National Museum of Finland on Monday evening (24.1.2006)

Helsingin Sanomat