It's 8:30 on 4 January, 2010.
Commuters are crowded onto platforms at Helsinki's Central railway station. Suddenly, four railway cars, weighing a total of 250 tonnes, become detached and start to accelerate downhill toward the passengers.
Three platform guards spring into action. They get everyone out of the way - just in the nick of time. Just 13 seconds later, the four cars slam through the buffers and crash into a nearby hotel.
Rescue forces estimate that the guards had just 60 seconds to clear the platforms.
How were the guards able to take such timely action?
Their TETRA radios made the difference.
Rail traffic control officers used the TETRA radio network to alert the guards the instant the automatic brakes that should have stopped the cars failed.
With the commuters safe, only the guards were left in the area as the runaway cars came crashing into the station. The guards managed to dive for cover as the cars careened through the buffers and came to rest - embedded some five metres deep into an adjacent building.