Asphyxiating

In order to transport gasses in as big an amount as possible, many are transported pressurized. In case of a leak, as the gas is equalized with atmospheric pressure, it will take much greater volume than the tank it was transported in. This can cause dislocation of oxygen around the train, potentially leading to suffocation of people and animals in its vicinity. This is called asphyxiation.

Apart from being hazardous, asphyxiating gasses have a positive side too. In case of a leaking accident, because they remove oxygen from an area, they can help extinguish fires.