Hydrogen explosion caused the Helsinki City Theatre incident

The Finnish Safety and Chemicals Agency (Tukes) investigated what caused the explosion at Helsinki City Theatre on 29 June 2020, and the results are now ready. The explosion was caused by hydrogen gas that got into the sprinkler room from the sprinkler system’s pipes during the system’s maintenance. Together with indoor air, it formed a flammable mix of hydrogen gas and air. There have been no prior incidents in Finland, so it could not have been prepared for.

Hydrogen gas forms in the pipes of a sprinkler system as a result from corrosion when zinc, oxygen and water react. The mix of hydrogen gas and air is extremely flammable. The exact cause of ignition remains uncertain in the Helsinki City Theatre incident. 

To avoid other similar incidents, Tukes issues instructions and recommendations for companies that design and maintain sprinkler systems as well as property owners. Tukes also instructs that new sprinkler systems should no longer have pipes that are coated with copper inside. Installations already under construction can be finished as planned, but the possibility of hydrogen forming in the pipes should be taken into account to ensure safety. A dangerous situation may arise when the sprinkler pipes are emptied or altered. 

Tukes instructions and recommendations:

– The use of zinc-coated pipes in new sprinkler systems must cease in Finland. Tukes will later announce a schedule for operators in the field. 

–  Zinc-coated sprinkler pipes may form hydrogen gas, which can leak out during maintenance or other work on the sprinkler pipes, forming a flammable mix of hydrogen gas and air. This should be taken into account when assessing the danger of explosion and when required to draw up an explosion protection document.  You can read more information on the safety of explosive facilities here (in Finnish).

– Sprinkler fitters must use a detector for hydrogen gas when emptying sprinkler pipes. 

–  A company that maintains sprinkler systems must device instructions for their employees that covers the ventilation of a facility, use of gas detectors, observation of pipe pressure, protective equipment and other equipment thought necessary.

–  The sprinkler room’s ventilation is ensured and boosted if needed when the sprinkler pipes are emptied or altered. 

Further information: Senior Officer Jan Meszka, tel. +358 29 5052 061, email format: [email protected] 

Tukes studied the incident in cooperation with VTT, Helsinki City Rescue Department, DEKRA Industrial Oy, KIWA Inspecta, Alarm Control Oy, Finance Finland, the Finnish National Rescue Association, Sprinkleritekninen Yhdistys ry and Suomen Palopäällystöliitto.