Possible connection between Museokatu gas leak and National Museum explosion under investigation

Some parts of Helsinki gas network nearly 100 years old

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The cause of Monday’s explosion at the National Museum in Helsinki remains uncertain. Police have not ruled out a connection between the blast and a gas leak found later on the adjacent street of Museokatu.
      There are two theories on the cause of the explosion. According to the first, natural gas leaking from a ruptured gas main in Museokatu entered the National Museum through the sewage system, or conduits for electric lines. The National Museum is not on the gas grid.
      The second theory is that the methane that caused the museum explosion came from the sewage system itself, and could not get out because of faulty or frozen ventilation.
     
Helsinki Water has favoured the first theory from the start. "The only possibility for gas concentrations this high is that there would have been a leak in the gas network into the sewer", says Antero Hakkarainen of Helsinki Water.
      The water utility found explosive concentrations of gas in a well at the southern end of Museokatu on Tuesday evening. Restaurants near the area were evacuated as a precaution.
      The area was closely monitored during the evening; gas gauges were lowered into sewage pipes to detect high concentrations of gas, which were found in several locations. The leak was pinpointed at the location where the highest gas levels were found.
     
The head of customer services at the gas company Gasum, methane expert Arto Riikonen, feels that the connection between the explosion and the gas leak is very unlikely, although he does not rule it out completely.
      "The leak in the natural gas line, and the break in the sewage pipe should be at the same location, for the gas to enter the sewer. Typically, there is about a metre of earth between these pipes", Riikonen says.
      He adds that methane is generated wherever there is a swamp, a bog, or, for instance, a cow. "It took 150 million years in Siberia, it takes a year at a landfill, and in a cow, it takes one day."
      "Explosive amounts of methane can collect in a drain pipe, if enough time passes. The decisive question is, when the ventilation broke in the drainage system at the National Museum.
     
The police investigation at the museum concluded on Wednesday morning. Laboratory tests are still being conducted to ascertain that the substance that caused the explosion really was methane.
      "We want to make sure that none of the substances in the cleaning closet caused the explosion. However, this does not seem likely. If the cause of the explosion came from the drain, methane is the main suspect", says Kari Tolvanen of the Helsinki police.
      "We cannot say with certainty if the methane came from the gas network. We are studying the matter for the sake of overall security, but there is no criminal investigation."
     
The gas mains near the museum date back to 1911. Helsinki has a total of 200 kilometres of gas lines, one third of which are old cast iron, or steel pipes. They are constantly being replaced by more flexible plastic pipes.
      The cause of the rupture in the gas main was not the age of the pipe, but rather shifts in the ground caused by changes in temperature. The Museokatu pipe was most recently inspected in the summer of 2005.
      Jarko Alanko, managing director of Gasum subsidiary Suomen Kaasuenergia, insists that Helsinki’s gas network is safe.
      "We feel that it is in operational condition. We do business here every day."


Previously in HS International Edition:
  Methane leak causes several evacuations in downtown Helsinki (25.1.2006)

Helsingin Sanomat