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Pyrophoric Compressed Gases

Pyrophoric gases react so rapidly with air and its moisture that the ensuing oxidation and/or hydrolysis lead to ignition.  Ignition may be instantaneous or delayed.  Spontaneous (instantaneous) ignition or combustion occurs when a substance reaches its ignition temperature without the application of external heat. The hazards are pyrophoric fires, explosions and/or deflagrations, and autoignition of a vapor cloud.  All of these conditions can occur depending on leak location, excess flow control and shutdown of the pyrophoric gas.  Pyrophoric fires are difficult to extinguish.  When pyrophoric fires are extinguished, the gas supply must be shut down promptly by interlocks tied into fire protection and/or detection system, because resulting pyrophoric gas build up has the potential to create vapor cloud detonation.

The quantities of pyrophoric gas that can be stored and used on the floor of a building or within a control area is strictly regulated by the VSFPC, and the allowable quantities decrease for every story above ground level. 

Examples

  • Silane

Precautions

  • All pyrophoric gases MUST be stored in a continuously, mechanically ventilated gas cabinet, fume hood, or other enclosure (unless otherwise recommended by the supplier). Please contact EHS for guidance or assistance.
  • Review the Safety Data Sheet to determine safe use guidelines.
  • Remote manual shutdown devices for pyrophoric gas flow must be provided outside each gas cabinet or near each gas panel. Automatic shutdown devices for pyrophoric gas flow activated by interlocks tied into fire protection and/or detection must be provided.
  • Pyrophoric gas flow, purge, and exhaust systems must have redundant controls that prevent pyrophoric gas from igniting or exploding. These controls include excess flow valves, flow orifices, mass flow controller sizing, process bypass line elimination or control, vacuum-pump inert-gas purging, dilution of process effluent with inert gas and ventilation, controlled combustion of process effluent, ventilation monitoring, and automatic gas shutdown.
  • Emergency back-up power must be provided for all electrical controls, alarms and safeguards associated with the storage and process systems for pyrophoric gases.
  • All process systems components and equipment must be adequately purged using a dedicated inert gas cylinder.
  • New users MUST consult with EHS before ordering pyrophoric gases.
  • Pyrphoric gases are not allowed in unsprinklered buildings unless prior approval from EHS has been obtained.
  • Certain mixtures of gases, such as 1.5% silane/98.5% nitrogen are not considered to be pyrophoric or flammable, and if you can use these nonflammable gas mixtures for your work, that should be a priority. Please contact EHS for guidance on other gas mixtures.
  • Order the smallest sized cylinder you can that will support your research, and do not purchase and store spare cylinders.