Any structure containing hydrogen components should be adequately ventilated when hydrogen is in the system. Suspended ceilings, inverted pockets, confining cowlings, or covers that might accumulate hydrogen should be avoided or adequately ventilated. The local release of hydrogen into the laboratory should be controlled by enclosures and vented to the outside to prevent it from reaching an ignition source. Ventilation systems should not be used for the disposal of hydrogen; this should be managed through a separate vent system. See Proper Storage, Use and Venting

Basic Requirements

  • Ventilation rates, at a minimum, should be sufficient to dilute hydrogen leaks to 25% of the LFL; that is about 1% by volume for gaseous hydrogen for all credible operation and accident scenarios.
  • Where passive ventilation is used, adequate ventilation to the outdoors should be provided. Inlet openings should be located at floor level in exterior walls. Outlet openings should be located at the high point of the room in exterior walls or roof. Inlet and outlet openings should have a minimum total area of 0.003 m2 per 1 m3 of room volume, or 1 ft2 per 1,000 ft3 of room volume, per 29CFR 1910.106.
  • Normal air exchange should be 0.3 m3 of air per minute per 1 m2 of solid floor space, or 1 ft3 of air per minute per 1 ft2 of solid floor space.
  • Laboratories and laboratory hoods in which hydrogen is present should be continuously ventilated under normal operating conditions.
  • The minimum ventilation rate should safely dilute hydrogen buildup due to leakage from system components. Ventilation should not shut down as a function of emergency shutdown.

Supply Systems

  • The supply system should meet basic requirements.
  • Laboratory ventilation systems should be designed to ensure that supply air to the laboratory does not contain hydrogen re-circulated from another system’s exhaust.
  • The air pressure in the laboratory should be negative with respect to corridors and non-laboratory areas.
  • The location of air supply diffusion devices should be chosen to avoid air currents that would adversely affect the performance of fume hoods and exhaust systems.

Exhaust Systems

  • The exhaust system should meet basic requirements.
  • Air exhausted from fume hoods should be released, and under no circumstances re-circulated or allowed to enter other ventilation intakes unless designed in accordance with ANSI/AIHA Z9.5. Since hydrogen is lighter than air, the exhaust from fume hoods and special exhaust systems should be discharged above the roof.
  • Air from laboratories in which hydrogen is present should be continuously discharged through duct systems maintained at a negative pressure relative to that of normally occupied areas of the building.
  • Positive-pressure portions of the laboratory hood exhaust systems (e.g., fans, coils, flexible connections, and ductwork) located within the laboratory building should be sealed airtight or located in a continuously mechanically ventilated room.
  • Fume hood face velocities and exhaust volumes should be sufficient to contain hydrogen released within the hood and exhaust it outside of the laboratory building.
  • The hood should prevent leakage of hydrogen whenever it is present in the hood.
  • Special local exhaust systems (e.g., snorkels) should have sufficient capture velocities to entrain the hydrogen being released.
  • Duct airflows must be sufficient that hydrogen concentrations in ducts in probable release scenarios must be kept below LFL.
  • Canopy hoods should not be used unless an evaluation shows that they can adequately capture any released hydrogen gas.
  • Since hydrogen is lighter than air, the exhaust from fume hoods and special exhaust systems should be discharged above the roof.
  • Automatic fire dampers should not be used in fume hood exhaust systems.
  • Fire detection and alarm systems should not be interlocked to automatically shut down fume hood exhaust fans.

Fans

  • Fans should be selected to meet requirements for fire, explosion, and corrosion.
  • Where hydrogen is passed through the fans, the rotating element should be of non-sparking construction, or the casing should be constructed of or lined with such material.
  • Nonferrous or spark-resistant materials should have a flame spread index of 25 or less when tested in accordance with NFPA 255.
  • Fans should be marked with an arrow or other means to indicate direction of rotation and with the location of fume hoods and exhaust systems served.