D1b.2 external static electricity and ignition in hydrogen distribution pipelines

This report describes the results of the study into electrostatic discharge under realistic conditions that can lead to the ignition of hydrogen-air mixtures outside gas transport and distribution systems. This was prompted by the increasing transport and distribution of hydrogen, where the lower (concentration-dependent) minimum ignition energy (MIE) and broader flammability limits lead to a higher susceptibility to ignition compared to natural gas (at certain concentrations).

This raises the question of the extent to which electrostatic discharge can lead to the ignition of hydrogen-air mixtures in practice, and to what degree this risk is relevant for working on gas infrastructure. This involves the use of components such as those applied by Dutch grid operators.

The research is based on a combination of literature review and experiments. Initially, the extent to which electrostatic discharge can occur to components in the gas network was investigated. Subsequently, it is determined experimentally under which conditions this discharge can actually lead to the ignition of a hydrogen-air mixture (during maintenance activities or outside the pipeline).

The results demonstrate that electrostatic discharge from a person to a component can occur under realistic conditions. So-called conductive components, such as metal pipes and valves, exhibit consistent discharge even at relatively low voltage levels (2–4 kV). These voltages fall within a range which can quite easily be generated by people during everyday activities, particularly under dry conditions (<50 RH%).

Additional testing in a controlled environment shows that an electrostatic discharge can actually lead to the ignition of a hydrogen-air mixture under certain conditions. It appears that ignition is highly dependent on the hydrogen concentration and the potential difference. With approximately 10 vol% hydrogen in air, ignition can occur at voltage levels of 4–8 kV. At lower hydrogen concentrations, higher voltages are required than tested, or no ignition occurs.

The experiment confirms that the physical potential for ignition is present. At the same time, the results show that the effective ignition energy is highly dependent on the manner in which the discharge takes place. Only a portion of the available energy is effectively transferred to the gas mixture, where factors such as discharge location, geometry, material properties, distance, and environmental conditions are determined.

Although the theoretical possibility of ignition has been proven, practice shows that the combination of circumstances required for it becomes systematically systematic. For ignition, the following is required simultaneously:

• a flammable hydrogen-air mixture
• an electrostatically chargeable person or object
• a discharge at a location where the energy is effectively influenced

Within the current working methods of grid operators, this combination is prevented by existing safety measures. For example, work is not permitted at flammable concentrations (>10% LFL), personal protective equipment must be used, and professional competence is prioritized through training, instructions and supervision.

It can therefore be concluded that the risk of ignition due to electrostatic discharge is sufficiently mitigated in current practice. Safety is based partly on avoiding the circumstances under which ignition can occur, and not on excluding static electricity as a physical ignition mechanism.

The results provide insight into the underlying mechanisms and confirm that electrostatic ignition is physically plausible but is operationally controlled within current working practice. Overall, the factors underline the importance of continued attention to and correct application of existing safety measures, particularly given the higher susceptibility of hydrogen to potential ignition compared to natural gas.