Risk Assessment Methodology
A common methodology for coarse risk assessment, Rapid Risk Ranking (RRR), was adapted to take into account specific issues at a public hydrogen refuelling station, see ref. /2/ and /3/. This methodology is suitable for early concept risk evaluations, and further details about the methodology can be found in ref. /2/.
A RRR is carried out as a group session. The group consist of persons with expert knowledge of and experience with the item/process being analysed, representing different disciplines such as process, electronics and instrumentation, machinery etc. A person with risk analysis experience will usually lead the analysis and a secretary report the results.
During the group sessions hazards were identified, and assessed with regard to the probability of their occurrence and their consequences. The probability and consequences are categorised based on “semi quantitative” probability and consequence classes, - probabilities varies from “never heard of” to “occurs several times a year”, whereas the consequence varies from “several fatalities” to “minor injury or annoyance”. The resulting risk of the identified hazards, which is a combination of probability and consequences are then compared to a risk matrix, where the risk is classified as Unaccepatbly High, Medium or Acceptably Low, dependent on the probability/consequence combination. If the risk is High, a more detailed risk analysis should be carried out, and risk remedial actions might be required. For Medium risk, a more detailed risk analysis should also be carried out, for example a cost benefit analysis.
Description of refuelling station concepts
A gaseous hydrogen filling station based on onsite production of hydrogen can be divided into several main blocks, see illustration in figure 1: