[holding answer 11 June 2007]: It is not clear what type of assessment the question refers to. The trial is ongoing and the results will be assessed in due course to improve our understanding of the movement of material in the urban environment.
Further discussions have taken place in respect of the planned second phase of the trial which will be undertaken in early 2008 following analysis of the first phase results.
We encourage the publication of research results but this may be restricted for reasons of national security.
[holding answer 11 June 2007]: The non-toxic gases used in the trial belong to the family of chemicals known as cyclic perfluorocarbons. The actual gases released are: perfluoro methyl cyclohexane; meta perfluoro dimethyl cyclohexane; and para perfluoro dimethyl cyclohexane.