If you are ever caught up in a gas attack from tear gas (lacrimators), simply soak any piece of fabric or cotton pad with urine and hold to your nose as a mask. The ammonia in urine will neutralize the tear gas.
In chemical warfare, more dangerous gases like chlorine gas are used. It is seen as floating yellow-green gas with a strong smell of bleach. Urine remains a potent defence against this gas but you also need to get to clean air and higher ground because Chlorine gas (choking gas) is denser than air and settles in low-lying areas. Like the name implies, "choking gas" causes trouble with breathing.
I hope you never need to use your urine this way but it is worth noting and sharing.