D6A.4 General recommendations: applicability of QRA tools, detection of hydrogen fires, effectiveness of odorisation, and effect of hydrogen permeation

In HyDelta 2.0's work package "Safety of hydrogen in the distribution network and the built environment", research has been conducted on the risks of hydrogen through a quantitative risk model and additional experiments around the effect of ventilation on the accumulation of gas in a home. In addition to these two main tasks, a number of smaller topics related to the same main objective were conducted. These knowledge gaps were identified during HyDelta's scoping phase and may lead to additional measures in the pilot projects. They are:

1. Are existing QRA tools applicable for hydrogen gas pressure regulating stations?
2. Is flame detection necessary for hydrogen fires?
3. To what extent is the effectiveness of barrier odorization affected by, for example, adsorption and/or absorption of the odorant?
4. What is the effect on safety and gas quality of the permeation of nitrogen, oxygen and water from outside the pipeline to the inside?

Based on literature review, these 4 questions were answered.

Applicability of existing QRA tools for hydrogen gas pressure regulating stations

The most common and available tools for performing a so-called Quantitative Risk Assessment (QRA) were assessed and compared. For the comparison, it was specifically examined which tools would be suitable for determining the risk contours around a so-called gas pressure regulating stations operating on hydrogen.

The application area and scope of each tool were analysed. From the analysis it was concluded that the software tools Safeti-NL and Conifer are suitable for determining the risk contours around a gas pressure regulating station, with the former being accepted by the Dutch competent authorities as an unequivocal calculation method for facilities for performing a QRA. Conifer is less well-known in the Netherlands and at this point in time does not have the option of being licensable but has been specifically developed for that part of the gas network from the gas pressure regulating station (<8 barg) to the gas meter (20 – 25 mbar). Taking into account the validation programs of both tools, it is expected that the risk contours of both tools around a gas pressure regulating station will largely overlap. Both tools have been validated for use with natural gas and the validation with hydrogen is steadily being expanded. Based on the current validation datasets, the risk contours for the same situation for hydrogen are greater than those for natural gas. It should be noted that for both software tools - in case of hydrogen - worst case scenarios are used with the calculations. For example, the ignition probability of hydrogen is set to 100% by default. Such parameters have a clear influence on the risk contours. Knowing that the validation process is still in full swing, it is therefore not appropriate to make a statement about how the risk contours of hydrogen and natural gas relate to each other in terms of size. Comparing the first results, it is expected that after full validation the difference will be limited.

Detection of hydrogen fires

A hydrogen flame may be less visible depending on the circumstances. Reduced visibility may result in injury to persons when they get too close to the flame. Currently, there is a lack of experience with hydrogen flame visibility under various conditions. Because the experience is lacking, it is recommended that tools be made available for service technicians in pilot projects to detect a hydrogen flame and make them aware of the possible presence of a hydrogen flame. With the experience gained during the pilot projects and additional research, it can be determined whether future flame detection tools should be available for work on hydrogen grids. Gathering of information on the visibility of burning odorized hydrogen and the visibility of flames during incidents is recommended.

Determining the effectiveness of THT odorant

Based on the literature review, it was determined that, in specific situations, the effectiveness of odorization by THT can be negatively affected. Despite this influence, the effectiveness of odorization of hydrogen by THT is comparable to that of natural gas. With this, there is no reason to take additional control measures when distributing hydrogen odorized with THT.

Determining the effect on safety and gas quality due to permeation of nitrogen, water and oxygen

Permeation is a natural phenomenon that occurs in both natural gas and hydrogen distribution. As long as there is gas flow through the pipelines, the effect with respect to safety and quality is negligible. In situations where there is a isolated pipeline section, based on a theoretical consideration, there will be an effect with respect to safety and quality over time. This consideration considered the permeation of individual components, oxygen, nitrogen and water, from outside the pipeline to inside the pipeline. In order to understand the total process of permeation and its effect on safety and gas quality, it is recommended that pilot projects monitor the gas composition especially in situations where there is long-term shutdown of hydrogen in pipelines.