These are our sources of information:
http://en.wikipedia.org/wiki/Chemical_weapons_in_World_War_I
http://www.historylearningsite.co.uk/poison_gas_and_world_war_one.htm
http://www.firstworldwar.com/weaponry/gas.htm
http://www.livescience.com/39248-what-is-mustard-
http://www.answers.com/Q/How_did_Poison_Gas_affect_people_in_World_War_1
http://science.howstuffworks.com/mustard-gas2.htm
http://www.historylearningsite.co.uk/gas_masks_in_world_war_one.htm
http://www.compoundchem.com/wp-content/uploads/2014/05/Chemical-Warfare-World-War-1-Poison-Gases.png
http://upload.wikimedia.org/wikipedia/commons/7/7b/Vickers_machine_gun_crew_with_gas_masks.jpg