When operating any machinery, safety is paramount. When that machinery is old, safety is even more important. Everything should be carefully engineered, and nothing can be left to chance!
In a steam engine, the most prominent safety feature is the relief valve. It protects the boiler from exploding by relieving the pressure well before its exceeds the design limits. Relief valves are checked on a regular basis by a solid engineering company specializing in this type of job.
We got lucky to see this procedure done on the 6060. "You might want to close your ears", the guys told us. "There will be a lot of noisy steam coming out!"
Just as they said that, the sound came - very impressive indeed! - and a huge column of steam rose to the skies. I guess, the valves worked!