"There was a bang and then I was running with the rest through smoke. Thick, grey smoke has covered thirty years at least"(Carol Ann Duffy, 1941 stanza 1 line 4-6)
The Poet used the The imagery in the quote such as "Thick, grey smoke has covered thirty years at least" to show how the Woman in the underground began to loose her identity. When the smoke covers her not only is it covering her face but her identity, her whole life.