So how would they know what it was other than what they were not going to try and help obvious victims in distress only after getting the lab report. They have seen far more chlorine so how are first responders, especially in a third world war zone, to know what agent it is that is killing the victims right now. Seconds mattered as far as their perspective was concerned.
If you are in a war zone you need to know what the effects of these agents are and what victims of the different agents look like. One clue, turning blue, unconscious, and having seizures, you are too close already.