Can water mist be used in tunnels? I wondered that for a long time, and with every tunnel project, many questions around this issue were piling in my head. When dealing with large infrastructure projects you really need to work your way around multiple functional aspects of a system - maintenance, water and power consumption,  drainage capacity, availability of elements and their certification... You would love to focus purely on the fire safety aspect of the issue, but you cannot. Unfortunately, this is often the world of fire engineering. And in this world, we make decisions based on what we know about systems - and when we don't know enough - we test it! And for the water mist question, I've found the perfect person to give me some answers.  Johny Jessen from VID Fire Kill has visited me in my office and told me about his experience with full-scale fire tests of water mist systems in a tunnel, carried by Efectis. You know he is serious about what he is doing when you learn that the fire source used for this test was approx. 250 MW! This discussion goes deep into the testing and the differences between suppression systems and challenges that modern engineers face in landmark projects. Johny has asked me to invite you to his LinkedIn profile, where he shares a lot of great resources related to water mist technology - so here you go! And the VID Fire Kill profile. You may also like to check this whitepaper on the experiments carried in Spain that we discussed in this episode. More materials, including videos of the test, can be found on the project website. I must also give a shoutout to friends at Efectis who have done some really great job engineering these fire tests! From one fire science enthusiast to another, hats down.