Electrical Classification

Depending on the amount of hydrogen that is expected to exist in a workspace, the National Electrical Code (NFPA 70) requires certain types of electrical equipment to be used.

Electrical equipment must conform to the applicable electrical classification and must be suitable for hydrogen service. Fans for active ventilation systems should be provided with a rotating element of nonferrous or spark-resistant construction, or be constructed of, or lined with, such material.

Other equipment or devices should be constructed in a similar manner and designed for use in hydrogen service.

Motors and their controls not approved for hydrogen service should be located outside the location where hydrogen is generated or conveyed.

Other equipment not conforming to the National Electrical Code requirements must be located outside the area classified as hazardous.

NFPA 70 classifications relevant to hydrogen include:

  • Class I: Locations in which flammable gases or vapors are or may be present in the air in quantities sufficient to produce explosive or ignitable mixtures (see Article 500)
  • Division 1: flammable or explosive mixtures may exist under normal operating conditions, or during maintenance (leaks), or because of system breakdown/faulty operation of equipment
  • Division 2: flammable or explosive mixtures are only present under abnormal conditions (i.e., accidental rupture or breakdown of the containment vessel), or systems where ignitable concentrations are prevented by positive mechanical (active) ventilation, or systems adjacent to Class I/Div 1 locations where vapors might migrate.
  • Hydrogen is classified as a Group B gas.
  • The autoignition temperature for hydrogen is 585°C (1085°F).