-Just a remark: "Yperite" [first used near Ieper/Ypres] is a liquid "Blistering Agent". No gas.
Depending on the meteo conditions: viscosity. Stickiness...Contamination of everything: meant to deny the enemy the use of a certain stretch of terrain.
-Eyes and exposed skin are the first to be harmed. [Temporary-permanent blindness]...These wounded will have to be treated in separate Dressing Stations after being decontaminated.
-in a second stage the drops of agent on uniform, equipment, weapons, tools start to evaporate and are inhaled. Blistering the mucous membranes and the lungs. So even when leaving the contaminated zone....everything will still be contaminated...for days...weeks...and the troops will contaminate the new sector, shelters.trenches... they go to...
-that is why it is better to use the term: Agent.
-The Germans use the term "Chemische Kampfmittel".
-And yes: there is a difference in mask filters to be used for the different Agents. A difference between vape and gas.