Authorities in southwestern England are testing an air ambulance, emergency vehicles and clothing worn by emergency workers who responded when two people were poisoned with a nerve agent in June.
The county of Wiltshire police force described the testing for traces of Novichok on Wednesday purely as a precaution "to ensure that no onward contamination has taken place."
Police say the air ambulance will be grounded until the tests are completed.
Dawn Sturgess and her partner, Charlie Rowley, were taken ill months after former Russian spy Sergei Skripal and his daughter were poisoned with Novichok in March.
Police think the couple handled a bottle containing the military grade nerve agent developed in the Soviet Union.
Sturgess died, but Rowley and the Skripals survived.
Police say the risk to the public remains low.
