Managing the high-risk, high-potential dilemma of hydrogen

Managing the high-risk, high-potential dilemma of hydrogen

Low-emissions hydrogen has the potential to play a central role in the energy transition from fuelling transport and powering industry to generating electricity and heating our homes and businesses.

But, this high-potential element, is highly reactive when it is mixed with air. Careful management is required to prevent sparking a major incident while optimising the opportunities that it offers.

Understanding the ignition properties of hydrogen

When mixed with air, it takes just a small amount of energy to ignite hydrogen. In fact, it has a minimum ignition energy (MIE) 1 of only 0.017 mJ making it extremely volatile. Methane, ammonia, propane, and butane, by comparison, have considerably higher MIEs ranging from 0.25mJ for propane to 14mJ for ammonia.

On the other hand, when considering ignition at hot surfaces the auto ignition temperature of hydrogen (520 °C) is comparable to that of methane (600 °C) and propane (450 °C). A significant difference is however that a hydrogen-air mixture only needs a very short contact time to be ignited compared to e.g. methane (induction time hydrogen 0.01 s versus 20 s for methane) which makes hydrogen-air mixtures far more vulnerable for short duration hot surfaces generated by e.g. single impacts.

The 13 hydrogen ignition sources

1. Hot surfaces: Hazards of ignition by static hot surfaces such as caused by hot equipment is comparable to that of hydrocarbons such as ethane and propane.
2. Flames and hot gases: Flames are very effective ignition sources. A hot gaseous jet can ignite when its temperature exceeds 670 °C.
3. Mechanically generated friction and impact: Friction and rubbing between two moving surfaces can cause hot surfaces and mechanical sparks able to ignite hydrogen even at relative velocities between these moving surfaces < 1 m/s which for other flammables is considered a safe limit. Also single collisions between two objects can cause momentary hot surfaces or mechanical sparks able to ignite hydrogen-air mixtures. Material combinations involved can have a big influence on the incendivity.
4. Electrical equipment: Design in accordance with established standards (IEC 60079-series) can prevent ignition of hydrogen-air mixtures.
5. Ground currents, cathodic corrosion protection: Stray currents may cause a potential difference between different earthing points. This can be avoided by bonding all parts of the equipment which are electrically conductive.
6. Static electricity: In the light of the low MIE of hydrogen strong attention shall be given to earthing and bonding of electrically conductive equipment. The surface area of non-conductive parts of equipment liable to become electrostatically charged shall be limited depending on the probability of being exposed to a flammable hydrogen-air mixtures (< 400 mm² in zone 0; < 2000 mm² in zone 1; see IEC 80079-36). Avoid the presence of sharp objects in strong electric fields to avoid the occurrence of corona discharges.
7. Lightning: Design of lightning protection in accordance with the IEC 62305 standard will reduce the probability of lightning becoming an ignition source
8. Electromagnetic waves frequency range 10⁴ Hz to 3x10¹² Hz: Radio transmitters may cause induction currents in large dimension loops (e.g. equipment). At locations of poor contact in these loops sparks may occur. Hydrogen-air mixtures are easily ignited
9. Electromagnetic waves frequency range 3.10¹¹ Hz to 3x10¹⁵ Hz: Ignition by optical radiation due to indirect heating of objects (energy absorption). The minimum ignition power for hydrogen-air mixtures is > 100 mW.
10. Ionization radiation: Indirect ignition due to energy absorption of X-ray radiation or radioactive sources by particles.
11. Ultrasound: Indirect ignition of objects due to absorption of ultrasound is possible at sound level pressures exceeding 178 dB.
12. Adiabatic compression and shock waves: Shock waves occurring after the opening of a bursting disc as an over pressurisation protection of a storage unit containing hydrogen venting into a vent line mix hydrogen with air and can ignite the mixture due to shock wave reflections.
13. Exothermic reactions: An exothermic reaction causes high temperatures and possibly open flames which can ignite a hydrogen-air mixture. The hydrogen may be a product of the chemical reaction such as occurring when fine light metal particles come into contact with water.
    

Mitigating the risk of hydrogen ignition

The successful use of hydrogen, and ammonia, as part of the energy transition pivots on industry’s ability to safely use them.

Asset integrity and risk management: The high diffusivity, small molecular weight and low viscosity of hydrogen make it easy for hydrogen to escape through small cracks and joints. Robust asset integrity and risk management programmes are critical.

Every asset must have the proper leak, gas, and fire detection and mitigation systems in place while zoning and segregating areas within plants reduce risks and makes incident management easier.

Regulatory compliance: Long-established industry standards that inform the design and operation of industrial plants that utilise hydrogen form the foundation for the safe production, transportation, and use of hydrogen. However, given the complex nature of projects involving hydrogen, it’s impossible for these to cover every possible scenario and should be regarded as the starting point for risk mitigation.

Important standards and guidelines are:

ISO/TR 15916 Basic considerations for the safety of hydrogen systems: identifies the hazards and risks when using gaseous or liquified hydrogen. It provides safety guidelines for its use and storage.

NFPA 2 Hydrogen Technologies Code: a prescriptive standard presenting high level, hydrogen-specific requirements for buildings, outdoor storage, and applications such as fuelling facilities, electrolysers, parking garages etc.

In addition, there are many standards addressing safety for certain applications such as:

ISO 19880-1 Gaseous hydrogen - Fuelling stations Part 1: General requirements.

ISO 23273 Fuel cell Road Vehicles - Safety specifications: Protection against hydrogen hazards for vehicles fuelled with compressed hydrogen.

There are also codes for prevention of ignition of hydrogen atmospheres such as the IEC 60079-series and the 80079-36 and -37 putting demands to electric and non-electric equipment respectively for use in potentially explosive atmospheres incl. hydrogen.

Quantitative risk management
Vysus Group has a vast experience performing quantitative risk assessments of oil and gas installations. Vysus Group developed tools to assess the frequency of both releases of flammable materials and the frequency of ignition: PLOFAM and MISOF. These tools are currently being used as a basis to predict the probability of release and ignition of hydrogen.

The consequences of ignited hydrogen releases are assessed with established tools such as Phast and the CFD tools KFX and FLACS. These tools have all been developed to include the effects of hydrogen (jet) fires and explosions. Special attention is given to possibility of a transition to detonation of hydrogen-air clouds. A developing deflagration in hydrogen-air mixtures easily transits into a detonation implying that the entire flammable part of the cloud would detonate causing stronger blast waves into the surroundings, thereby potentially causing more damage.

Vysus Group is a global leader in risk management and safety. Decades of domain knowledge of the risks associated with production, transportation and use of hydrogen and ammonia coupled with game-changing digital tools put us in a unique position.

We identify risks, we help prevent accidents from happening, and we contribute to reducing the consequences should unwanted incidents occur. We look at technical, physical, organisational and human factors as part of a holistic approach to controlling risk and ensuring safe operations.

To find out more get in touch with our team here.