An in-depth technical report by Professor Dimitrios Karonis of the National Technical University of Athens (NTUA) has provided answers to key questions about the massive explosion that followed the devastating Tempi train crash. The report was commissioned by the appellate investigator overseeing the case.
The 123-page forensic study is based on detailed analyses from Greece’s General State Chemical Laboratory, on-site inspections, material samples from the crash site, and international scientific data. Professor Karonis concludes that silicone-based transformer oil from the trains likely played a critical role in the formation of the intense fireball. According to the expert, this type of oil can ignite at temperatures of 330°C or higher, potentially leading to a fireball under the conditions present during the accident.
The report supports the hypothesis that no flammable cargo was involved in the crash and that the most probable cause of the fireball was a combination of electrical arcing and the subsequent ignition of silicone transformer oil from the trains involved.
The report has been submitted to appellate judge Sotiris Bakaimis for review. It will be considered alongside other forensic assessments, some of which support similar conclusions, and others that contradict them. These include findings from technical consultants representing victims’ families and the Hellenic Fire Service. All reports will be evaluated by the court and the investigating judge.
Key Conclusions from the Report
What Caused the Fireball
According to data from the Hellenic Railways System Operation Control and Safety Center, three intense flashes—interpreted as electrical arcs—were recorded in video footage of the crash. These flashes ceased when an overload protection system was triggered, manually, from the remote power control station in Thessaloniki.
This observation suggests that a fireball could indeed have formed as a result of high-intensity electrical arcing. Given that these arcs were captured on video, this mechanism is seen as a plausible cause of the fireball in the Tempi crash.
Possibility of Flammable Cargo – Why Hydrocarbons Were Ruled Out
The report also considers the possibility that a flammable substance—such as a hydrocarbon—could have been involved. In such cases, fireballs can form from flammable vapors released when a container ruptures.
To evaluate this scenario, the study references internationally accepted models, including one developed by TNO (Netherlands Organization for Applied Scientific Research). These models use parameters like fireball diameter and duration to estimate the quantity of fuel involved. Based on video footage, the fireball’s diameter was estimated at approximately 80–85 meters, suggesting that between 2,300 and 3,100 kg of flammable material would have been necessary to produce such an explosion.
The TNO model and one from the UK’s Health and Safety Executive (HSE) both indicate that for a flammable vapor cloud to form and ignite, the material’s flash point must be below the ambient temperature at the crash site.
According to Greece’s National Meteorological Service, the temperature in Tempi at the time of the accident was about 10–11°C, with 85–90% relative humidity. Therefore, the substance responsible for such a vapor cloud would need a flash point lower than 10°C.
However, neither the cargo manifest nor the Greek Police’s on-site inspection report mention any material with those characteristics. Additionally, three open freight cars were carrying only sheet metal, as confirmed by security footage from tunnels and checkpoints prior to the crash. No signs of tanks or containers holding flammable liquids were observed.
The remaining freight cars, which were sealed containers, showed no fire damage and either contained goods listed on the manifest or were empty. There is no evidence of any flammable cargo capable of creating the vapor cloud necessary for a fireball.
Silicone Oil as the Likely Fuel
The report also analyzes the possibility of the fire originating from transformer cooling oil in the electric locomotives.
Silicone-based transformer oil can ignite if ambient temperatures exceed 300°C. Under normal operating conditions, however, the oil temperature remains around 90°C—well below its ignition point. According to Hellenic Train’s technical documentation, transformer winding temperatures above 155°C and oil temperatures above 90°C are considered excessive.
Therefore, under normal circumstances, the oil would not ignite. However, after the fireball formed—potentially due to an electrical arc—it is plausible that the silicone oil contributed to the resulting fire due to the extreme heat.
