One of the dead villagers, an old man, can clearly be seen breathing during the opening scenes of the episode.
The helmet Solo puts on clearly has gaps over the shoulders and in front, which would give him no protection from whatever airborne danger they put on the helmets to avoid. The infection is unidentified. Also, the chopper windows appear to be open while on the ground, so taking off their helmets would expose them to whatever airborne danger they're trying to avoid.
At the beginning when they throw the incendiary grenades, the fire starts off to the right of where the grenade landed.