From petrol station to multifuel energy station: Changes in fire and explosion safety

A multifuel energy station is a publicly available station which offers refueling of traditional fossil fuels in combination with one or more alternative energy carriers, such as hydrogen or electric power to electric vehicles. The goal of this study is to survey how the transition from traditional petrol stations to multifuel energy stations affects the fire and explosion risk.

Relevant research publications, regulations and guidelines have been studied. Four interviews with relevant stakeholders have been conducted, in addition to correspondence with other stakeholders. The collected information has been used to evaluate and provide a general overview of fire and explosion risk at multifuel energy stations. The scope of the project is limited, and some types of fueling facilities (in conjunction with supermarkets, bus- and industrial facilities), some types of safety challenges (intended acts of sabotage and/or terror), as well as transport of fuel to and from the station, are not included.

Availability of different types of fuel in Norway was investigated and three types were selected to be in focus: power for electric vehicles, gaseous hydrogen, as well as hydrogen and methane in liquid form. The selection was based on expected future use, as well as compatibility with the goal of the National Transport Plan that all new vehicles sold from 2025 should be zero emission vehicles. Currently, the category zero emission vehicle includes only electric- and hydrogen vehicles.

In facilities that handle flammable, self-reactive, pressurized and explosive substances there is a risk of unwanted incidents. When facilities with hazardous substances comply with current regulations, the risk associated with handling hazardous substances is considered not to be significant compared to other risks in society. When new energy carriers are added, it is central to understand how the transition from a traditional petrol station to a multifuel energy station will change the fire and explosion risk. Factors that will have an impact include: number and type of ignition sources, number of passenger vehicles and heavy transport vehicles at the station, amount of flammable substances, duration of stay for visitors, complexity of the facility, size of the safety distances, fire service’s extinguishing efforts, environmental impact, maintenance need etc. In addition, each energy carrier entails unique scenarios.

By introducing charging stations at multifuel energy stations, additional ignition sources are introduced compared to a traditional petrol station, since the charger itself can be considered as a potential ignition source. The charger and connected car must be placed outside the Ex-zone in accordance with NEK400 (processed Norwegian edition of IEC 60364 series, the CENELEC HD 60364 series and some complementary national standards), in such a way that ignition of potential leaks from fossil fuels or other fuels under normal operation conditions is considered unlikely to occur. A potential danger in the use of rapid charging is electric arcing, which can arise due to poor connections and high electric effect. Electric arcs produce local hot spots, which in turn can contribute to fire ignition. The danger of electric arcs is reduced by, among others, communication between the vehicle and charger, which assures that no charging is taking place before establishing good contact between the two. The communication also assures that it is not possible to drive off with the charger still connected. There are requirements for weekly inspections of the charger and the charging cable, which will contribute to quick discovery and subsequent repair of faults and mechanical wear. Other safety measures to reduce risk include collision protection of the charger, and emergency stop switches that cut the power delivery to all chargers. There is a potential danger of personal injury by electric shock, but this is considered most relevant during installation of the charger and can be reduced to an acceptable level by utilizing certified personnel and limited access for unauthorized personnel. For risk assessments and risk evaluations of each individual facility with charging stations, it is important to take into account the added ignition sources, as well as the other mentioned factors, in addition to facility specific factors.

Gaseous hydrogen has different characteristics than conventional fuels at a petrol station, which affect the risk (frequency and consequence). Gaseous hydrogen is flammable, burns quickly and may explode given the right conditions. Furthermore, the gas is stored in high pressure tanks, producing high mechanical rupture energy, and the transport capacity of gaseous hydrogen leads to an increased number of trucks delivering hydrogen, compared with fossil fuels. On the other hand, gaseous hydrogen is light weight and easily rises upwards and dilute. In the case of a fire the flame has low radiant heat and heating outside the flame itself is limited. Important safety measures are open facilities, safe connections for high pressure fueling, and facilitate for pressure relief in a safe direction by the use of valves and sectioning, so that the gas is led upwards in a safe direction in case of a leakage. For risk assessments and risk evaluations of each individual facility with gaseous hydrogen, it is important to take into account the explosion hazard, as well as the other mentioned factors, in addition to facility specific factors.

Liquid hydrogen (LH2) and liquid methane (LNG, LBG) are stored at very low temperatures and at a relatively low pressure. Leakages may result in cryogenic (very cold) leakages which may lead to personal injuries and embrittlement of materials such as steels. Critical installations which may be exposed to cryogenic leakages must be able to withstand these temperatures. In addition, physical boundaries to limit uncontrolled spreading of leakages should be established. Evaporation from tanks must be ventilated through safety valves. During a fire, the safety valves must not be drenched in extinguishing water, as they may freeze and seal. Leakages of liquid methane and liquid hydrogen will evaporate and form flammable and explosive gas clouds. Liquid hydrogen is kept at such a low temperature that uninsulated surfaces may cause air to condense and form liquid oxygen, which may give an intense fire or explosion when reacting with organic material. For risk assessments and risk evaluations of each individual facility with liquid hydrogen and liquid methane, it is important to take into account the cryogenic temperatures during storage and that it must be possible to ventilate off any gas formed by evaporation from a liquid leakage, as well as the other mentioned factors, in addition to facility specific factors.

For the combination of more than one alternative energy carrier combined with fuels of a conventional petrol station, two areas of challenges have been identified: area challenges and cascade effects. Area challenges are due to the fact that risks to the surroundings must be evaluated based on all activity in the facility. When increasing the number of fueling systems within an area, the frequency of unwanted incidents at a given point in the facility is summarized (simply put). If two energy carriers are placed in too close proximity to each other, the risk can be disproportionately high. During construction, the fueling systems must be placed with sufficient space between them. In densely populated areas, shortage of space may limit the development. Cascade effects is a chain of events which starts small and grows larger, here due to an incident involving one energy carrier spreading to another. This may occur due to ignited liquid leakages which may flow to below a gas tank, or by explosion- or fire related damages to nearby installations due to shock waves, flying debris or flames. Good technical and organizational measures are important, such as sufficient training of personnel, follow-up and facility inspections, especially during start-up after installing a new energy carrier. The transition from a traditional petrol station to a multifuel energy station could not only give negative cascade effects, since sectionalizing of energy carriers, with lower storage volume per energy carrier, as well as physical separation between these, may give a reduction in the potential extent of damage of each facility. Apart from area challenges and cascade effects no other combination challenges, such a chemical interaction challenges, have been identified to potentially affect the fire and explosion risk.

For future work it will be important to keep an eye on the development, nationally and internationally, since it is still too early to predict which energy carriers that will be most utilized in the future. If electric heavy transport (larger batteries and the need for fast charging with higher effect) become more common, it will be necessary to develop a plan and evaluate the risks of charging these at multifuel energy stations. For hydrogen there is a need for more knowledge on how the heat of a jet fire (ignited, pressurized leakage) affects impinged objects. There is also a general need for experimental and numerical research on liquid hydrogen and methane due to many knowledge gaps on the topic. During operation of the facilities and through potential unwanted incidents, new knowledge will be gained, and this knowledge must be utilized in order to update recommendations linked to the risk of fire and explosion in multifuel energy stations.