• Flammable range of gaseous hydrogen in air is 4-75% by volume
• Colorless, odorless, tasteless, flammable, nontoxic
• Lightest know gas
• Burns almost invisibly
• Hydrogen can detonate (explode at supersonic velocity) in air over a range of approximately 18% to 59% by volume
• Diffuses through air, porous materials; may dissolve and diffuse through metals
• Hydrogen embrittlement – weakening effect on steel, copper, nickel, Cu-Ni alloys
• The discharging of hydrogen from high pressure to low pressure is heated; do not open valves on cylinders to remove dust or dirt from fittings; hydrogen cylinder must be equipped with a protection plug at the gas outlet
• Can be an asphyxiant hazard

Engineered Controls

Hydrogen Storage

• Must be in a division approved location protected by sprinklers.
• Ventilation to effectively ensure an explosive concentration does not develop.
• Hydrogen cylinders or associated paraphernalia must not be situated within 3 feet of any required exit.
• The area within 20 feet of a hydrogen container is to be separated from stored flammable materials and oxidizing gases.
• Inventory limits:
  • 4 standard cylinders (200 cu ft. ea.) in a laboratory equipped with sprinklers
  • Up to 8 cylinders in an exhausted enclosure/flammable gas cabinet (the number of cylinders not in use must not exceed four cylinders)
  • Cylinders containing mixed gases with a total flammable component or components less than 10% by volume (e.g., typical calibration gases) are not included in the calculation of allowable inventory unless the safety data sheet (SDS) specifically defines the gas as flammable

• The concentration of hydrogen used in any process must be the minimum amount necessary.
• Evaluation of potential ignition sources such as static electricity, heat generating equipment, flames, tools, and equipment. Note: A practical alternative to the elimination of all ignition sources is to prevent an explosive atmosphere by providing adequate ventilation or the prevention of hydrogen leaking out to encounter an ignition source.
• Evaluation of potential combustibles.
• Flow limitation of no more than 200 % of the rate needed to perform the experiment or operation.
• Enclosures must be vented to a safe location to minimize accumulation of hydrogen gas.
• All hydrogen systems must be purged with an inert gas before operation.  The purge operation must be repeated when the operation is shut down, restarted.  The purge cycle needs to be at minimum 4 system volume changes.  Methods of confirmation of the presence of hydrogen, water vapor, air, should be employed to determine the effectiveness of the purge process.
• Flashback arrestors must be on hydrogen supply lines and located immediately downstream of the first regulator or other location evaluated by the safety review.
• Non sparking exhaust fans.
• Hydrogen equipment must be designed and approved for hydrogen service and installed in accordance with the manufacturer’s instructions and recommendations.
• Continuous hydrogen detectors, when provided, must be listed by a national recognized testing laboratory (NRTL), calibrated, installed, maintained, and tested in accordance with the manufacturer's recommendations.

• Volume of room, laboratory, enclosure, or hutch where hydrogen is used.
• Exhaust flow rate of ventilation systems to be used.
• Pressure relief valves piped to a laboratory exhaust.
• Electrical equipment to conform to NFPA 70 and NEC Article 501.
• Equipment is considered cylinders, containers, piping, tubing, manifolds, regulating devices, flashback arrestors, and other accessories such as portable gas detectors for detecting and measuring hydrogen.  Maintenance, calibration, and inspection of equipment should be performed.
• Laboratory equipment using low concentrations of hydrogen must be vented to outside of the building in appropriate equipment, ductwork, hoods or a burning system.
• Do not modify pressure relief valves and regulating equipment.
• Compatibility of materials and equipment with hydrogen use.
• In case of an emergency DIAL 911 from an Argonne phone or 630-252-1911 from a cell phone.

Procedural Controls – All experiments and operations (including any preparatory/setup/testing work in the LOM laboratories) involving the storage, use, or generation of hydrogen must undergo a documented safety review.

Written operating procedures and instructions are required to define start up, shutdown, normal and emergency operations, and purging.  Line supervisors are responsible for the preparation and approval of the operating procedures.

Controlled access to regions where hydrogen is stored and used must be restricted to qualified personnel.

Post Warning Signs:  "Warning. Hydrogen – Flammable Gas. No open flames."

All hydrogen systems must be leak tested with helium and soap solution under near conditions of temperature and pressure with which the experiment or process will undergo.  Leak checking must be done if the hydrogen system is modified.  Leak checks should be performed periodically as well.

Qualified personnel who have been made conscious of the hazards associated with hydrogen. The training involves the safe operation of facilities containing hydrogen, and prior consultation and confirmation of knowledge of emergency notification, emergency shutdown, and emergency response procedures

Signs and Labeling – Contact the ESH Divisional Coordinators for signs.

Personal Protective Equipment – Safety glasses with side shields and safety shoes when handling gas cylinders.  Heat resistant gloves for high temperature hazards.

Monitoring – Continuous hydrogen detectors.

ANL Pressure Safety Manual, Volume 1 (2022) (Internal Link)

ANL Pressure Safety Manual, Volume 2 (2022) (Internal Link)