"The most spectacular (and most dangerous) examples of GIC impact were two destructive fires-the first in Sweden around 02:00 GMT on 15 May and the second in the United States around an hour later. The Swedish event occurred in a telephone exchange in the town of Karlstad, 260 km west of Stockholm. This event was widely reported around the world... It was also the subject of contemporary study by David Stenquist, a Swedish scientist and engineer, who had a long interest in what we would now call GIC impacts on telecommunications systems. One of his narrative reports on the event is included in his 1925 memoir on earth currents (Stenquist, 1925), and another is reproduced by Karsberg et al. (1959). They both outline how the operators at Karlstad exchange first experienced problems (equipment anomalies and faint smoke) around 01:00, followed by a period of quiet, before the main fire started around 02:00 leading to extensive equipment damage. Stenquist also highlighted a near-miss incident at Ånge, some 380 km north west of Stockholm, that was simultaneous with the Karlstad fire. This experienced a threat similar to that fire, but where the initial problems were sufficient to trigger preventive measures that avoided major damage. In his later analysis of the Karlstad fire (Albinson, 2018; Engström, 1928; Stenquist, 1925), Stenquist noted that this site was vulnerable to strong GIC, because it was on the 400 km route of the major communications lines between Oslo and Stockholm, and this route was vulnerable because of its east-west orientation. His insights into engineering design of the communications lines enabled him to estimate the geoelectric fields that created the damaging GIC. He showed that fields of at least 6 V/km were required to cause the observed melting of fuses, "tubes de fusion," in copper wires, and that a field of 20 V/km would have caused more damage than observed (melting of fuses in iron wires). As a result he suggested that 10 V/km would be a reasonable estimate of the average geoelectric field in central Sweden at the time of the Karlstad fire." (Hapgood).

"Over the past decade the public perception of space weather has changed markedly so that it is now considered a major societal risk alongside other natural hazards including pandemic disease, extremes of temperature, coastal and river flooding, earthquakes, and volcanic activity. As a result of this step change in public perception, improved understanding of severe space weather, and its impacts, is now a vital element in the scientific evidence sought by policy-makers responsible for societal resilience. Those policy-makers require information on both the likelihood, and the adverse impacts, of severe space weather, just as they do for other natural hazards. Only then can they integrate space weather into wider plans to ensure societal resilience against the whole range of natural hazards.
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A key element in this evidence is the likely timelines of extreme space weather events. Such knowledge enables us to build scenarios that give insights into the spatial and temporal distribution of adverse impacts, and into the information that will be available to enable timely decision-making before, during and after an extreme event. They are also vital for exercises to test mitigation plans and to train key personnel in government and industry. Scenarios are also critical inputs for realistic studies on the socio-economic impact of space weather.
This study addresses one route to scenario development, namely, a review of previous severe space weather events, and specifically focuses on one outstanding case, the great storm of 13-16 May 1921, and particularly the very intense activity on 14/15 May." (Mike Hapgood: Space Weather. The Great Storm of May 1921: An Exemplar of a Dangerous Space Weather Event).