Episode #4.3 - S4-E3
Deliberate mistake: Before the gas explodes in the sewer, you can see the base of the Davy lamp glow red. Except that in real life this doesn't happen; the flame simply turns blue and grows taller in the presence of gas. This was probably done to make the scene more dramatic, though.
Episode #4.7 - S4-E7
Factual error: In this episode Blackwall Station is shown as a London Underground tube station. Blackwall Station is a Docklands Light Rail (DLR) station. Also look at the destination sign on the front of the train, which reads 'THAMES LINE', No such line/station exists on the London Underground.
Episode #4.9 - S4-E9
Continuity mistake: In an early shot of the factory fire. Appliance registration C389GFC is at the fire...but Blackwall have not been mobilised to the fire yet.
Episode #4.9 - S4-E9
Revealing mistake: In a scene in the mess, Sicknote walks in front of the television and there are grey stickers stuck to the screen to hide the production spotlights.
Episode #4.9 - S4-E9
Continuity mistake: Later when the crews are trapped C389GFC is arriving as a new appliance even though it has already been there.
