What is Lessons Learned?

What is H2LL?

This database is supported by the U.S. Department of Energy. The safety event records have been contributed by a variety of global sources, including industrial, government and academic facilities.

H2LL is a database-driven website intended to facilitate the sharing of lessons learned and other relevant information gained from actual experiences using and working with hydrogen. The database also serves as a voluntary reporting tool for capturing records of events involving either hydrogen or hydrogen-related technologies.

The focus of the database is on characterization of hydrogen-related incidents and near-misses, and ensuing lessons learned from those events. All identifying information, including names of companies or organizations, locations, and the like, is removed to ensure confidentiality and to encourage the unconstrained future reporting of events as they occur.

The intended audience for this website is anyone who is involved in any aspect of hydrogen use. The existing safety event records are mainly focused on laboratory settings that offer valuable insights into the safe use of hydrogen in energy applications and R&D. It is hoped that users will come to this website both to learn valuable lessons from the experiences of others as well as to share information from their own experiences. Improved safety awareness benefits all.

Development of the database has been primarily supported by the U.S. Department of Energy. While every effort is made to verify the accuracy of information contained herein, no guarantee is expressed or implied with respect to the completeness, causal attribution, or suggested remedial measures for avoiding future events of a similar nature. The contents of this database are presented for informational purposes only. Design of any energy system should always be developed in close consultation with safety experts familiar with the particulars of the specific application.

We encourage you to browse through the safety event records on the website and send us your comments and suggestions. We will continue to add new records as they become available.

How does H2LL work?

If you have an incident you would like to include in the H2LL database, please click the "Submit an Incident" button at the top of the page. You will be asked for a wide range of information on your incident. Please enter as much of the information as possible. In order to protect your and your employer's identities, information that may distinguish an incident (your contact information, your company's name, the location of the incident, etc.) will not be displayed in the incident reports on H2LL.

Lessons Learned Corner

Visit the Lessons Learned Corner Archives.

Key themes from the H2Incidents database will be presented in the Lessons Learned Corner. Safety event records will be highlighted to illustrate the relevant lessons learned. Please let us know what you think and what themes you would like to see highlighted in this safety knowledge corner. You can find all the previous topics in the archives.

A process area alarm activated. The alarm was caused by an instrument channel located above a reaction vessel off-gas system final HEPA filter canister, which indicated 25% of the lower explosive limit (LEL) for hydrogen. Since the only source of hydrogen is from the reaction vessel during the reaction of sodium with concentrated sodium hydroxide, the immediate actions were to shutdown the reaction process and place the facility in a safe condition.

The root cause was inadequate or defective design. Had the pre-filter drains been vented to outside the building, no hydrogen could accumulate in the process area. The corrective action for this is to complete an Engineering Task Authorization (ETA) to install a sample/drain collection system with loop seals to prevent any release of view more

While research staff were working in a lab, a staff member opened the primary valve to a 0.2" (1500 psi) hydrogen gas line connected to a manifold supplying instruments in the lab. Upon opening the valve, the hydrogen gas line failed at a fitting on the switching manifold, releasing a small amount of hydrogen gas. The staff member closed the valve immediately, then inspected the gas line and found the front ferrule (of the compression-style fitting) to be missing. There were no injuries or damage to equipment.

In the follow-on discussion with research staff, it was learned that approximately one month earlier, a similar condition (front ferrule missing from a fitting) was found while performing a modification to a similar manifold. Following a critique, management expressed view more

An unplanned shutdown of the hydrogen supply system occurred, affecting the hydrogen furnaces in the plant. The apparent cause was an inadvertent valve closing, which was contrary to the written procedure.

A preventative maintenance activity was being conducted on the hydrogen gas system. Shortly after starting that work, various hydrogen gas users notified the emergency response personnel that the hydrogen supply safety alarms sounded, indicating an interruption of the hydrogen gas supply. As a result, the hydrogen furnaces shut down. This shut down is an automated process which injects an inert gas (nitrogen or argon) to prevent the introduction of oxygen and its mixing with any hydrogen gas. All shut downs functioned as designed. As a precautionary measure, fire protection view more

Incident Synopsis
During development tests, a gaseous H2 test tank was over pressurized and ruptured. The tank dome was destroyed.

The pressure relief valves were set too high. In addition, the tank was not depressurized while being worked on. Safe distances, as required by the procedures for personnel safety, were not followed.

Incident Synopsis
During transfer of liquid H2 from a commercial tank trailer to a receiving vessel, a leak developed in a bayonet fitting at the trailer/facility connection. The leak produced liquid H2 spray which enveloped the rear of the truck where the hand-operated shutoff valve was located. Emergency trained personnel, wearing protective clothing, except for proper shoes, entered the area and shut off the flow control valve. Reentry personnel suffered frost bite of their feet when shoes became frozen to the water-wetted rear deck of the truck.

A loose hose flange connection allowed leakage of cold fluid through the lubricated bayonet seal. This allowed cold fluid to contact and shrink the 'O' ring seal (made of Buna-N rubber), thus permitting view more

Incident Synopsis
While disconnecting a liquid H2 fill line from a liquid H2 trailer, liquid H2 escaped, burning a second man who was holding the hose. The man was burned on his hands and on his stomach.

The liquid H2 shut off valve was partially open, but both men assumed it was closed. Prescribed clothing was being worn.

Incident Synopsis

A hydrogen compressor had been shut down for repairs and was being put back into service when an explosion occurred, resulting in property damage. The compressor was equipped with interchangeable intake and outlet valves.


The discharge valve was installed in the intake valve position, causing the cylinder head to blow off and release H2 to the atmosphere. The ignition source was not indicated.

Incident Synopsis
A H2 air explosion occurred near a H2 compressor, located outside. Gaseous H2 had been released from a vent stack when a relief valve was actuated. The source of ignition was not known, but considerable damage was inflicted onto the system by the ensuing fire and explosion. Following the explosion, the shut-off valves were closed and the system was vented.

Two relief valves were located in the 3,000 psig system downstream of a 5,000/3,000 regulator. The relief valves were sized to handle substantially different flows. (One was designed for another program.) The relief valve was believed to have opened when the pressure setting was being increased from 2,700 to 2,900 psig. The accuracy of the 5,000 psig gauge used to control the dome of the 5 view more

A faulty modification to a multiple-gas piping manifold allowed mixing of hydrogen and oxygen that resulted in a storage tube explosion. Several employees suffered severe burn injuries from the incident.

Incident Synopsis
An employee, without authorization, fabricated and installed an adapter to connect a hydrogen tube trailer manifold to an oxygen tube trailer manifold at a facility for filling compressed-gas cylinders for a variety of gases, including hydrogen, oxygen, nitrogen, and helium. A subsequent improper purging procedure allowed oxygen gas to flow into a partially filled hydrogen tube on a hydrogen tube trailer. An ignition occurred in the manifold piping system and a combustion front traveled into the hydrogen tube where, after traveling about a view more

A hydrogen leak occurred from a 1-inch gate valve on a makeup gas line in an oil refinery gas oil hydrotreater unit. When the leak was discovered, the gas oil hydrotreater unit shutdown procedures were immediately implemented and emergency response was requested. The refinery response team along with county response teams responded, and after approximately 1/2 hour, the gas oil hydrotreater unit was fully shut down. Shutdown consisted of sufficiently depressurizing the unit and adding nitrogen to allow safe closing of the leaking 1-inch gate valve and installation of the associated missing bull plug.

During this event, the 1-inch gate valve was found to be open roughly 10% with no bull plug in the valve, allowing the hydrogen to leak to the atmosphere. In addition, a 1-inch bull view more