No further information about the incident is given by CWGC and I have not been able to find any further details. If anybody can help, please get in touch.
I believe that the eligibility criteria for the CWGC register include any death while on duty in a civil defence role, even if this was not as a result of a bombing, etc.
Frederick Kiff was the father of the artist, Ken Kiff, who's pictures can be found via a Goodgle search, according to this website:
“It has long been wondered where Ken Kiff, the artist, now Associate Artist at the National Gallery, fits on the Kiff family tree and efforts are being made to pin him down. The results of the latest search have given us the following information. Kenneth G. Kiff was born in 1935 in Dagenham. He was the younger brother of Frederick Kiff born 1925. Their parents were Frederick W. Kiff and Miss Fawcett, who married in London Colney in 1925. Frederick W was a woodworker and later joined the Air Raid Patrol. Frederick W died in 1939, when Ken was four years old.”