 Hydrogen poses a number of hazards to human safety , from potential detonations and fires when mixed with air to being an asphyxiant in its pure , oxygen @-@ free form . In addition , liquid hydrogen is a <unk> and presents dangers ( such as frostbite ) associated with very cold liquids . Hydrogen dissolves in many metals , and , in addition to leaking out , may have adverse effects on them , such as hydrogen embrittlement , leading to cracks and explosions . Hydrogen gas leaking into external air may spontaneously ignite . Moreover , hydrogen fire , while being extremely hot , is almost invisible , and thus can lead to accidental burns . 
