'Poison gas' terror test on London Underground

Tests began today to see how potentially toxic substances would spread if used by terrorists on the Tube.

The Government trial was held at St John's Wood station on London Underground's Jubilee line.

Scientists released a harmless substance - sulphur hexafluoride - into all areas of the station, and then used equipment to check airflows and penetration levels.

The station remained open as normal for the one-day trial which will be repeated at St John's Wood next Sunday.

The results will be analysed by scientists from the Ministry of Defence's defence, science and technology laboratory.

The release of sarin gas in the Tokyo subway system in 1995 killed 12 people and injured nearly 6,000

The St John's Wood trials were announced earlier this month by Transport Secretary Douglas Alexander who made clear the tests were not a reaction to any threat increase or a measure to enhance security at Tube stations.

The St John's Wood 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.

Copyright Press Association 2007.

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