In today's episode, we go into the practical consequences of having an underventilated fire - that is the possibility of backdraught or other similar smoke explosion phenomena. My guest Dr Ricky Carvel from the University of Edinburgh, touches on the chemistry of combustion, explaining why the underventilated fire is different than the oxygen-rich one, and how flammability limits are critical in understanding dynamic phenomena that may occur in a fuel-rich environment. We go into conditions in which backdraughts occur, and how establishing flow-path or reducing smoke layer temperatures may be a way to mitigate the risk. Finally, Ricky shares on some future plans on how to give firefighters a real tool to assess the risk of backdraught.And of course, we had a ton of fun with the movie Backdraft, and to some extent the American spelling of the word.Some additional resources:Polish firefighters and door implosion video (around the 8th minute mark)  https://www.youtube.com/watch?v=ztrmC8o2UhUThe videos we created for firefighters can be found here: https://fire.eng.ed.ac.uk/techtalksOur short backdraught video from YouTube:https://www.youtube.com/watch?v=3kRoKckpJmEThe Slo-Mo Guys backdraft (sic) video:https://youtu.be/ZyCCWuO0mQo?si=NHKkG82clnPOTPbVTwo of our papers on backdraught/backdraft (FT uses American spellings!):https://doi.org/10.1016/j.firesaf.2017.04.003https://doi.org/10.1007/s10694-019-00914-9