This is a great little model - not only does it convey the event (as far as can be seen accurately as well), but is also a very interesting example of social commentary from the past............
The figures also quite accurately portray, in a very capable fashion, an air of panic.
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There is an interesting chart here on 4 of the major gases used in WW1 - although many more types than 4 were used.
http://www.compoundchem.com/wp-conte...son-Gases1.png
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And in terms of modern users don't forget Russia, who has weaponized stocks of nerve agents and other gases to hand, such as Sarin, Lewisite, Mustard, Soman, VX and Novichok (which was also the agent used in the recent Salisbury UK assassination attempt).