text: The assessments should indicate whether chemical weapons were used and if so the agent involved.
  The work could also reveal whether the weapons systems were improvised or designed for military use.
  The analysis being carried out by the Organisation for the Prohibition of Chemical Weapons under the auspices of the United Nations.
  Neither the UN nor the OPCW will comment on details of the investigation. But BBC News has spoken to a former senior employee of the OPCW, who has given his assessment of the likely details and timetable of the testing process.
  Dr Ralf Trapp said that samples from Syria gathered by inspectors had arrived at the OPCW central laboratory on Saturday and would be arriving at "designated laboratories" across the world around now for analysis. The results will form part of a report by the OPCW due to be published by the UN on the alleged attack. He told BBC News that the report would take between seven to 10 days to complete at the earliest.
  The report should contain strong scientific evidence to help establish whether chemical weapons were involved in the alleged attack last in the agricultural belt Ghouta around the Syrian capital Damascus. It could also possibly indicate the type of delivery systems to have been used, according to Dr Trapp.
  "There may be details of the concentrations of the agent used and whether these weapons were improvised or designed for a military context," he said.
  The purpose of the UN/OPCW report is to establish the facts of what happened rather than find the culprit. However, according to Dr Trapp, these facts should give an indication of the source. It will also help answer why, in his opinion, many of the victims did not display the typical symptoms of sarin exposure, such as the narrowing of pupils (known as pinball eyes) and shaking, in video clips uploaded shortly after the alleged attack.
  "I'm pretty sure it was a chemical attack, but I'm not 100% sure it was sarin, or sarin of bad quality, another agent, or a mixture of things. All these things make sense in the context of what we have seen (in the videos)," he explained.
  Last week OPCW and UN investigators were gathering soil, blood, urine and hair from the alleged victims of the attack and tissue samples from corpses. They have also been wiping possible chemical residues from the inside of shell fragments.
  There had been concern that few, if any, traces of nerve agent would be detected following the two days it took for UN inspectors to arrive at the site of the alleged attack. But according to Dr Trapp, evidence of these agents would remain for many weeks.
  The samples have been tagged, photographed and transported to OPCW's central laboratory in sealed containers. The testing procedures involve numerous checks and cross checks to ensure that there is no mix up in the samples and the results are accurate.
  Each sample is sent to three separate laboratories that the organisation has inspected and deemed competent to carry out the testing on its behalf. If there are many samples to analyse, they are sent to other laboratories. Individual labs conduct their own independent tests of the material.
  For each sample from the site of the alleged attack, a given laboratory receives two dummy samples; one containing no nerve agent and another containing a specified amount of a nerve agent or its breakdown product. The lab is not told which sample is which, enabling the OPCW to ensure that each lab does its job properly.
  In addition, a lab has to test each sample using two completely different methods - and then, as a triple check to verify the accuracy of the instruments they are using, manufacture the agent it thinks it has detected and run the test again to see if they obtain the same result.
  This painstaking process will take the scientists several days to complete, after which the lead investigator will have to write up a report which is then sent back to the OPCW.
  These results are combined with interviews, assessments of medical reports by inspectors.
  The time all this will take depends on the number of samples that have to be analysed and the number of labs involved in the testing.
  Dr Trapp believes that mid to late next week will be the very earliest that the UN could receive the completed report although Secretary-General Ban Ki-moon will be receiving regular updates in the interim.
  One of the testing sites on the OPCW's list of "designated laboratories" is the UK's Defence Science and Technology Laboratory (DSTL) at Porton Down in Wiltshire, which is internationally respected for its research capability in this area. The network of more than 20 laboratories also includes facilities in China, the US and France.
  The laboratories undertaking the work will have been selected by the OPCW's director-general Mr Ahmet Uzumcu, no doubt in consultation with Mr Ban. The list of institutions has not been revealed but there is speculation that laboratories in countries on the UN's Security Council are not involved.
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target: Samples from the sites of alleged chemical attacks in Syria are arriving at laboratories for analysis.