An old heating system had a common flu that effectively formed a full height chimney

An old heating system had a common flu that effectively formed a full height chimney
By Phil Murphy

Most flats had the old warm air systems (located behind a door like this, identifiable by the vent grill) removed when the communal heating was installed.
The high risk of an old common flu remained though because some leaseholders kept the old warm air systems.
Another high risk, full height, concealed and inaccessible cavity that travels unimpeded, vertically, between flats, from the first floor to the 23rd.