From the website:
"A photograph of a sentry outside Wellington Barracks, London, dressed in a full chemical protection suit and a gas mask, taken by Sayers for the Daily Herald newspaper on 10 February, 1938. The sentry was taking part in an air raid precautions exercise. A piece of specially-treated paper is attached to his bayonet. This acts as a detector which changes colour when gas is present, enabling the sentry to raise the alarm. The man in the background is a newsreel photographer who is carrying a cine camera. This photograph has been selected from the Daily Herald Archive, a collection of over three million photographs. The archive holds work of international, national and local importance by both staff and agency photographers."
In Collection of: National Museum of Photography Film & Television