On April 26, 2019, Russia submitted a critique (Note Verbale No. 759, pdf) of the March 1, 2019 OPCW Report (url). Like myself, Michael Kobs and others, it carried out reverse scientific calculations to estimate the drop altitudes which were possible for the very low impact velocities postulated by OPCW for the crater and cylinder damage.

It noted that the OPCW Report postulated impact velocities of 30 m/s for balcony cylinder at balcony floor (Figure A.6.7(b)), 50 m/s for balcony cylinder at hypothesized prior collision with roof above balcony (Figure A.6.6) and 60 m/s for the bedroom cylinder (Figure 10), but did not disclose the drop altitudes associated with these impact velocities. Russia estimated the drop altitudes at 45 to 180 meters. (For comparison, I had estimated drop altitudes of 50 to 150 meters for the balcony cylinder with slightly narrower range of impact velocities of 30 to 50 m/s.)

The Russian submission also stated that OPCW Figure 12 (about the bedroom cylinder) displayed results from a simulation of cylinders falling from 150 meters. The OPCW Report provided abysmally inadequate about its figures in general and no information on Figure 12 at all. The “H150” legend to Figure 12 (see below) seems to strongly support the Russian interpretation. Confirmation of this point would be welcome.







The Russian submission stated that Syrian Air Force helicopters fly above 2000 meters and that a cylinder dropped from such altitude would cause far more damage both to the roof and to itself.

In contrast, Syrian Air Force helicopters do not fly at altitudes of less than 2000

metres when cruising over towns, for security reasons. A helicopter flying at 200

metres over an active combat zone will come under fire from small arms at the least, and will be inevitably shot down. If a cylinder had been dropped from that altitude, it would have developed a vertical speed of about 200 m/s at the point of impact, and would have definitely not only destroyed the 20 cm thick roof, but would have caused more serious damage and would have been significantly damaged itself.

The leaked Engineering Report had reached identical (actually even stronger) conclusions. In their simulations, they observed that cylinders dropped from Syrian helicopter operating height of 2000 m had crashed through the concrete roof with far more damage than observed. Their results were even more conclusive. They did simulations down to 500 meters – far below operating heights – without changing the results.

OPCW Answer 8.1

The OPCW’s response to these important observations was both bureaucratic and refutable. It stated that its analyses were based on “facts and data collected and corroborated by the team and not on assumptions” about height of flight. Using these facts, the OPCW said that they carried out “reverse scientific calculations … to determine the range of force, velocities, and trajectories possible for the cylinder to have caused the damage observed at the site.” Here is their full Answer 8.1: watch the pea.

The analyses of the FFM are based on the facts and data collected and corroborated by the team and not on assumptions. In this context, the FFM report on the Douma incident does not contain assumptions or statements about the use of a helicopter (or any other craft) and the height of flight. The report does not provide information outside of the mandate and methodology of the FFM. Regarding the ballistics analysis, the methodology of the FFM is based on the collection of information and facts in relation to the physical measurements and properties: (a) dimensions, damage, ruptures, deformations, and other characteristics of objects at the locations (walls, ceilings, windows, furniture, etc.); (b) dimensions, damage, deformations, specific angles, and other characteristics of devices (cylinder(s) in the case of Douma, and munitions or other devices in other cases); (c) photographs and videos taken at the site of an alleged incident; (d) sample collection of different materials (besides looking for proof of toxic chemical exposure) looking for consistency/density/physical characteristics of different objects (walls, ceiling, furniture, various fragments etc.)

Based on these facts, modelling from physical measurements on site with reverse scientific calculations is used to determine the range of force, velocities, and trajectories possible for the cylinder to have caused the damage observed at the site. The FFM does not base its modelling or calculations on assumptions about the height from which the cylinder could have been dropped or the height of an aircraft. Therefore, in accordance with its mandate, the FFM did not comment on the possible altitudes of aircraft in any assumed operation modality.

The “Range of Force, Velocities and Trajectories”

OPCW says that they not only calculated the range of velocities but also calculated the range of trajectories possible for the cylinders to have caused observed damage. The calculation of a trajectory necessarily requires the calculation of drop altitude. Indeed, the calculation of drop altitude is precisely the sort of “reverse scientific calculation” which OPCW endorsed and said that it carried out.

While the OPCW asserted, with considerable pedantry, that its mandate was limited to “reverse scientific calculations” from observed facts, as though there was something wrong with forward scientific calculations from assumptions to test coherence with observations. Forward calculations are done all the time. Indeed, forward calculations, done iteratively, are arguably the primary mathematical tool for solution of reverse (inverse) problems. As noted above, the leaked Engineering Report contained forward calculations from various hypothetical drop altitudes to simulated damages – not just a reverse calculation. If the Russian interpretation of Figure 12 is valid, it was a forward calculation from a drop altitude of 150 meters. Finally, all the calculations of damages to cylinders and concrete roofs were forward calculations from assumed impact velocities. OPCW’s comments on this issue are absurd and incoherent.

In any event, had the OPCW reported the range of trajectories, readers would have been informed that the observed damage at the balcony corresponded to a drop altitude of only 50-150 meters. The inconsistency of this figure with known operating altitudes of Syrian helicopters would undoubtedly have been immediately pointed out, raising major questions about whether the chlorine cylinders could be attributed to a drop from Syrian helicopters as opposed to manual placement (as had been concluded in the leaked OPCW Engineering Sub-Team Report.