Tube services will run as normal
Tests have been held to see how toxic gas would spread if it was used by terrorists on London's Tube.
The trial took place at St John's Wood station on the Jubilee line, which operated as normal.
Non-toxic sulphur hexafluoride was released and then equipment checked as the gas drifted around the building.
The one-day trial will be repeated next Sunday. The results will be analysed by scientists at a Ministry of Defence laboratory.
The release of sarin gas in the Tokyo subway system in 1995 killed 12 people and injured nearly 6,000 others.
The St John's Wood trials were announced earlier this month by Transport Secretary Douglas Alexander who stressed the tests were not a reaction to any threat increase or a measure to enhance security at Tube stations.
The experiment follows trials of passenger screening technology at Paddington station in west London in January last year.
There were further trials at Canary Wharf and Greenford Tube stations.
Trials also took place last August to test the practicalities of deploying portable vehicle access control barriers at major entry points at Waterloo and Victoria stations in London.