The folks at Bellingcat published a piece titled Unpublished OPCW Douma Correspondence Raises Doubts about Transparency of “OPCW Leaks” Promoters. I was struck by the portions describing the unpublished letter, some of which contains interesting material concerning the OPCW’s methodology for identifying the use of chlorine gas:

What Wikileaks did not release was a letter drafted by several members of the OPCW in June 2019 and then sent by the director general of the organisation, Fernando Arias, in reply to a letter from Whelan.

In Whelan’s letter he claimed there was no evidence of chlorine being used as a weapon in Douma, and traces of chlorine that were found were not consistent with the release of chlorine gas.

In a draft version of the unpublished reply seen by Bellingcat, Arias explains why Whelan’s assumptions are wrong – he simply wasn’t aware of the latest scientific techniques used by the OPCW because they were developed after he left the organisation. It was these techniques that allowed the OPCW to conclude chlorine chlorine gas had been released in the building in which the Syrian civilians died.

In his letter, which was drafted with the input of several OPCW scientists, Arias wrote: “Your letter further refers to 2,4,6-trichlorophenol as being used erroneously as an indicator of chlorine exposure, and you rightly point out that this chemical can be present for a variety of reasons that do not require chlorine gas exposure. However, there were additional chlorine-containing chemicals found in samples taken from Douma, and in particular, chlorinated pinene compounds that have been shown to form in certain types of wood that have been exposed to chlorine gas.

One of the Designated Laboratories that analysed samples after you completed your tenure has developed methods or analysing wood exposed to chlorine gas that can distinguish between different types of wood in the signatures of chlorinated compounds produced. This laboratory’s analysis of wood samples taken from Douma indicated that the wood indeed had been exposed to chlorine gas. Whether background samples were analysed or not has no bearing on this very clear evidence. All chlorinated compounds identified, combined with all other available data and information, support the conclusion of the report in regard to chlorine. Moreover, the findings from the analysis of samples conducted after the interim report was issued, do not contradict conclusions reached by either the interim or final reports.

“In summary, the environmental samples collected from Douma provided information consistent with an environmental release of a toxic chemical for use as a weapon. The inability to take samples from the victims or attend post-mortem procedures precludes drawing any conclusions on cause of injury and death to humans, and this was correctly and clearly specified in the report.”