Hydrogen is a valuable resource with incredible potential. Over the past decade, industry has seen a broad resurgence in the use of hydrogen technologies. Unfortunately, with increased use comes an increased risk of incidents. Although some perceive hydrogen as an unsafe fuel, it has actually been used safely across a variety of industries for generations. Some of hydrogen’s properties actually make it safer to handle and use than many of today’s common fuels (e.g. hydrogen is non-toxic and much lighter than air, allowing leaks to dissipate quickly). Of course, other properties require special engineering considerations to help prevent an accident. The first step to safety is understanding. Read on to discover or refresh your knowledge on the unique hazards and learn more about WHA’s hydrogen fire risk analysis approach.

Our knowledge is built on experience

WHA’s hydrogen safety expertise is informed by years of failure analysis and forensic engineering. WHA’s engineers have investigated numerous incidents involving hydrogen and other hazardous fuels. The incident pictured above, for example, occurred at the Muskingum River Power Plant on July 8, 2007.

This tragic accident resulted from the release of hydrogen from a failed rupture disk on a storage vessel. A large quantity of hydrogen collected under a roof and ignited, killing one and injuring 10 others.

It’s our mission to prevent incidents like this. We have developed our suite of hydrogen consulting services and resources to help keep industry safe.

Problem: hydrogen presents a serious fire hazard!

In order to effectively communicate what’s required for a hydrogen fire to occur, WHA’s engineers often use the illustration of the “fire triangle.” There are generally three factors essential to ALL fires: fuel, oxidizer, and ignition. What we call fire is actually a “combustion” reaction: the chemical process of a fuel like hydrogen reacting with an oxizider, like oxygen. Under controlled circumstances, this powerful reaction can be harnessed for good. Under the wrong circumstances, a volatile hydrogen fire can be extremely destructive! Let’s review the properties of hydrogen that make it so unique.

Hydrogen is challenging to detect and contain

Hydrogen is a colorless, odorless, tasteless gas, and when it burns, it emits very little light and color. This makes hydrogen and hydrogen fires very difficult to detect without special equipment.  Furthermore, hydrogen holds a familiar place as the smallest element on the periodic table. In application, this means that its tiny H₂ molecules are very susceptible to leaks. They can diffuse through many materials considered to be “airtight.” Hydrogen can even absorb into certain metals, causing them to become brittle and crack (known as hydrogen “embrittlement”).

Hydrogen requires a low ignition energy

When hydrogen mixes with an oxidizer, it’s extremely easy to ignite. Gasoline, for instance, requires about 0.24 mJ of energy to ignite under the right conditions in air. This is less energy than generated from a small static discharge from your finger. By comparison, hydrogen only requires about 0.02mJ, 12 times less ignition energy than gasoline! You can probably imagine all the energy sources that are therefore capable of igniting hydrogen mixtures. Thus, it quickly becomes a dangerous situation if hydrogen finds its way out of a contained system.

Hydrogen has a wide flammability range

All fuels are only flammable when mixed in an appropriate ratio with an oxidizer, known as a flammability range. Unlike common hydrocarbon fuels (e.g. methane and propane), hydrogen has a very wide flammability range. It is vulnerable to ignition anywhere from 4-75% in air (and up to 95% in pure oxygen). This means that extra care must be taken to prevent leaks in hydrogen systems.

Solution: hydrogen risk management approach

In order to reduce the risk of fire, WHA engineers implement an approach based on three simple concepts: Avoid, Anticipate, and Adopt.  These words are placed around the fire triangle to reflect WHA’s larger risk management approach. By implementing this strategy and effectively eliminating even one leg of the fire triangle, the risk of a hydrogen fire can be mitigated:

1. Avoid Unintentional Mixing: By preventing accidental release and internal leaks in your hydrogen system, contained hydrogen remains in a concentration range which is not flammable and poses no fire risk. Design and material selection are of utmost importance for safe hydrogen systems.
2. Anticipate Ignition Mechanisms: With a very low minimum ignition energy required, ignition can occur readily from a wide variety of sources (e.g. electrostatic discharge, metal fracture, friction, shock waves, and even light). Although care must be taken to prevent ignition, users should assume an ignition source is present when a combustible hydrogen-oxidizer mixture has formed.
3. Adopt best practices: By implementing best practices for design, inspection, assembly, operation, maintenance, and safety systems, the risk of a hydrogen fire can be greatly reduced.

Next steps

WHA is dedicated to helping industry use hydrogen safely. Our specialized engineers are uniquely positioned to equip your staff with the tools and knowledge necessary to create and maintain a safe environment for everyone.

• Training: WHA provides web-based and on-site hydrogen safety training, custom-tailored for your unique application and needs. Course content is specific to the audience with progressive levels ranging from basic H₂ hazard awareness, operations and maintenance practices, system design, and H₂ fire risk analysis.
• Hazard Analysis: WHA’s Hydrogen Combustion Risk Analysis (HCRA) approach and expertise can be applied to assess component and system level hazards in your application. Our subject matter experts can help you identify risks and find solutions by providing recommendations on how to make your system safer.
• Testing: With both a laboratory test facility and WHA’s Proving Grounds (pictured below) for large or high-energy tests, WHA has the professional resources to provide custom and standard testing as well as research services.

Resources.

For more information on hydrogen hazards and best practices, see the following resources:

• H2 Tools (Lessons learned, Best safety practices, Materials database, and Safety Planning)
• NASA/TM-2016-218602 Hydrogen Embrittlement
• ANSI/AIAA G-095A Guide to Safety of Hydrogen and Hydrogen Systems
• ISO/TR 15916 Basic Considerations for the Safety of Hydrogen Systems
• CGA G-5-2017 Hydrogen