I remember runs out on the apron adjacent to base when the recirc fan burnt out at max diff filling the cockpit with smoke, not just normal smoke but the nice stuff containing hydrogen cyanide
the lads went on to 100% Oxy and told the outside guys to keep the fireman away from the door after declaring smoke up in the cockpit! fat chance! he was up the steps like sh*t off a shovel and was attempting to open the door at max diff! They got the quacks 100% oxy isn't good for you speech! but compared to hydrogen cyanide it was.