Theodore Scardino, one of the firefighters "significantly wounded" in the shooting in Webster, New York, has spoken since treatment, say Strong Memorial Hospital staff.
Scardino is able to breathe on his own, but staff said both he and Joseph Hofsetter were "at risk" and being monitored for bleeding.
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Mayor of London Sadiq Khan is backing the scheme.
Sunday will be a fine day across much of Scotland and northern England, with much less coastal mist and low cloud than yesterday.
A spokesperson said the lightning strikes had left the "aircraft fuelling system unavailable."