Data including density, flammability range, and auto ignition energy for hydrogen.

Properties | Value | Units |
---|---|---|

Auto ignition temperature [3,a] | 500-585 | °C |

932-1085 | °F | |

Boiling point (1 atm) [b] | -252.9 | °C |

-423.2 | °F | |

Density NTP [1,b] | 0.08375 | kg/m³ |

0.005229 | lb/ft³ | |

Diffusion coefficient in air NTP [1, a] | 0.610 | cm²/s |

6.57 E-4 | ft²/s | |

Enthalpy NTP [1, b] | 3858.1 | kJ/kg |

1659.8 | Btu/lb | |

Entropy NTP [1, b] | 53.14 | J/g-K |

12.70 | Btu/lb-°R | |

Flame temperature in air [a] | 2045 | °C |

3713 | °F | |

Flammable range in air [1,a] | 4.0 - 75.0 | vol% |

Ignition energy in air [c] | 2.0 E-5 | J |

1.9 E-8 | Btu | |

Internal Energy NTP [1, 2, b] | 2648.3 | kJ/kg |

1139.3 | Btu/lb | |

Molecular weight [b] | 2.02 | |

Specific gravity (air = 1) NTP [1, c] | 0.0696 | |

Specific volume NTP [1,b] | 11.94 | m³/kg |

191.26 | ft³/lb | |

Specific heat at constant pressure , Cp NTP [1, b] | 14.29 | J/g-K |

3.415 | Btu/lb-°R | |

Specific heat at constant volume, Cv NTP [1, b] | 10.16 | J/g-K |

2.428 | Btu/lb-°R | |

Thermal conductivity NTP [1, b] | 0.1825 | W/m-K |

0.1054 | Btu/ft-h-°R | |

Viscosity NTP [1,b] | 8.813 E-5 | g/cm-sec |

5.922 E-6 | lb/ft-sec |

Notes:

- NTP (normal temperature and pressure) = 20°C (68°F) and 1 atm
- Reference state: Internal Energy U=0 at 273.16 K for saturated liquid; Entropy S=0 at 273.16 K for saturated liquid.
- The autoignition temperature depends on hydrogen concentration (minimum at stoichiometric combustion conditions), pressure, and even the surface characteristics of the vessel. Reported figures range from 932-1085 oF according to source [a].

Source

a. ANSI/AIAA G-095-2004, Guide to Safety of Hydrogen and Hydrogen Systems