Electri-fired: The 1994 Zürich-Affoltern (Switzerland) Derailment and Fire
Background
Affoltern is a district of 26584 people (as of 2020) in the far north of Zürich in northern Switzerland, located 18.5km/11.5mi southwest of Winterthur and 27.5km/17mi north of Zug (both measurements in linear distance).
The district has a station on the Wettingen-Effretikon rail line, an electrified, mostly dual-tracked main line opening in 1877 under the “Swiss National Railway” (SNB, a private rail service provider). The fact that the rail line went around the industrial hotspot that Zürich represented was one of the main factors for SNB’s insolvency by 1878, with the line eventually ending up with the SBB (the actual Swiss national railway) by 1902. At the time of the accident the line was used for both regional passenger services and freight trains, including supply-trains to various local companies. By 1994 the section of the line west of Affoltern station was single-tracked, with the dual-tracked station serving as a siding for trains passing one another.
At the time an elevated high-voltage powerline carrying a 132kV current was running alongside the tracks in Affoltern, across the rail line from the station, 30m/98ft off the ground.
The train involved
On the day of the accident a locomotive of an unknown type was pulling a freight train from Birsfelden Harbor to Häggenschwil. The train consisted of 20 four-axle tank cars, fourteen of which carried unleaded “standard” fuel while six carried “Super Plus” high octane fuel. Each of the 20 cars measured 14.36m/47ft in length at an empty weight of approximately 23 metric tons and carried 80000l/21134gal of fuel.
The accident
On the 8th of March 1994 a freight train carrying fuel to Häggenschwil had departed Birsfelden harbor at 6:30am. The first hour and a half of the journey was uneventful, seeing the train steadily moving along until it approached the town of Regensdorf at approximately 7:55am. Here, 5km/3.1mi up the line from Affoltern station, the rear bogie of the seventh car lost its rear axle, which was ejected to the side beneath the following car. Regardless of the damage the train still moved along at 70kph/43.5mph, with the stricken car being held in line by its remaining three axles and the cars on either side.
The train kept moving along without issue despite the damage, making it through Regensdorf station and through some turns until it reached the points at the entrance to Affoltern station. Here the leading axle of the damaged bogie derailed as well, causing the train car to fully separate from the train at the following level crossing. The car left the rails to the left, rolling over and breaking through a concrete wall. Along its way it mowed down one of the support towers for the high voltage line (concrete poles measuring 60cm/2ft in diameter), tearing open the tank and bringing the voltage line down. Behind it the cars 8–10 derailed as well, most of them falling over and puncturing as they passed car 7. The separation of the train triggered an automatic stop in the forward section of the train as the pneumatic line for the brakes was ruptured, with the sudden drop in pneumatic pressure alerting the driver that something was wrong.
Sparks from the torn high voltage line immediately set the spilling fuel ablaze, likely aided by further sparking from the derailing cars sliding along the ground. Burning fuel spread around the wreckage and reached the drainage system, with several underground explosions launching manhole covers in the surrounding streets high into the air. The burning fuel also lit 3 adjacent apartment-houses on fire.
The Fire
The first call to emergency services was received at 8:05am, with 37 more calls coming in over the following 5 minutes. The dispatch-center was only staffed by two men at the time, with one handling most of the calls while the other coordinated the different units and was involved with the ever-increasing radio-traffic. The first firefighters reached the site of the inferno by 8:20am, finding themselves on the southern side of the rail line. They had planned to first tackle the fires in the adjacent buildings north of the rail line, which were now inaccessible to them due to the fire and closed level crossings. By the time of their arrival they could see that the three houses were completely engulfed in flames anyway, trying to safe the buildings or enter them to look for survivors would have been impossible either way.
Within minutes the fire had engulfed cars 7–10, was burning beneath cars 11–14 (which had remained upright), had reached 4 houses (3 of which were burning in entirety) and ignited several residents’ cars on the road. A handicapped resident from the fourth house was rescued by neighbors, the other 3 houses were empty. At 9:07am an explosion in the underground rainwater drainage system caused two passersby to be struck by a flying manhole cover, severely injuring them. One of the two individuals had been on horseback, causing the horse to suffer fatal injuries. Explosions kept rocking the area every few minutes, along with a constant whistle-sound from the intact tank cars’ overpressure valves trying to avoid an explosion. Several tank cars eventually exploded when the pressure inside increased too fast for the valves to keep it under control, often in the form of the lid blowing off the cars, followed by a towering flame.
The firefighters focused on limiting the spread of the fire both above and below ground, managing to contain the blaze on the surface enough for the SBB to send another locomotive by 9:10am, pulling a few intact cars from the rear of the train to safety before towing the forward part of the train away. The fire was declared extinguished by noon, by the afternoon remaining fuel could be pumped out of some burned train cars. In total almost 400 responders had been involved in the rescue and recovery-effort. Three people required hospitalization for injuries, 120 residents were evacuated and 23 people lost their homes. Half the train cars were destroyed in the blaze, along with the rail line, electric infrastructure and drainage systems as far as 800m/0.5mi from the site. Several roads were also damaged when underground explosions cracked the asphalt.
Aftermath
A small fire erupted the next day when workers, against the firefighters’ advice, used angle grinders and cutting discs to cut up the wreckage, causing, as the report puts it, “the few remaining manhole covers to be blown up as well”. After that incident the rest of the cutting was conducted with water cooled saws, generating less heat and no sparks. Once the wreckage was cleared contaminated soil had to be excavated, creating a pit 6m/20ft deep. Calculations based on the loading-protocols showed that 317000l/83700gal had burned, evaporated or seeped into the ground, another 148000/39000gal were pumped out of the damaged cars and disposed of.
Once the fire department left the site investigators descended on the charred remains of the freight train, trying to figure out what had caused the train to unleash hellfire on the unsuspecting residents. Car 7 itself had largely burned up, leaving little to be investigated. The investigators thus backtracked the path of the train into Affoltern, examining the level crossings, points and track. While any points that had survived the fire were in perfect working order scrapes and impact-damage to the track hinted at the cause, showing that the train had either been derailed or dragged something along well ahead of the site of the fire. Eventually investigators found the rear axle of car 7 sitting in a field just outside Regensdorf, appearing mostly in one piece.
Investigators found that one of the axle bearings which keep the outer end of the axles attached to the bogie had broken off, causing the loss of vital support. The bearings are intended as a way to reduce friction between the spinning axle and the heavy train car sitting on top. On modern train cars they are almost always constructed as roller bearings, utilizing a row of metal balls or cylinders between the outer (bogie) and inner (axle) component. Older journal-type bearings had a tendency of running hot/overheating if insufficient lubrication was applied, a problem much less likely to occur with the roller bearings. They can obviously still fail, usually by being worn down until they or single components within them become lodged. At that moment the resistance from the stopping bearing against the spinning axle can break the bearing apart. The axle bearings of train cars are a wear-item, with regular inspection and replacement being meant to keep the train car operating safely.
The investigation concluded that the last inspection of car 7 had been conducted improperly, failing to spot the worn axle bearing. Who exactly had been responsible for the axle-bearings during the inspection could unfortunately not be determined. The bearing notably hadn’t heated up significantly to draw attention or trigger an alarm from trackside heat-detectors, meaning once the last inspection ahead of the accident released car 7 into service there was no way to know a failure was imminent.
The ejection of the faulty axle from the train could have caused a derailment of the train right there and then, or possibly damaged the pneumatic lines to car 8 enough to trigger an emergency stop, but as neither scenario occurred the train was free to continue until the points ahead of Affoltern station derailed the other axle from the damaged bogie (which was missing significant lateral stabilization once the rear axle was gone) in a way that caused the passage of the adjacent level crossing to completely derail the train car, causing a separation of the train which triggered an emergency stop. At that point the following inferno was impossible to avoid, with car 7’s tank suffering a gash measuring 100x80cm/3x2.5ft. The spilling fuel immediately ignited, with the fire being fueled by the following cars also suffering punctures as they derailed.
There was no perfect short-term solution for the problem, with all the investigation could do being to recommend a review of maintenance-procedures and -cycles, making it less likely for worn/damaged axle bearings to slip through during inspections. A recommendation, at least, which the SBB happily accepted.
The soil was replaced and the rail line reconstructed in time for reopening on the 17th of March, with Affoltern station being rebuilt in a temporary form as the local section of the line would be upgraded to double-tracked configuration the following year. The old station-building lost its purpose and was since turned into a restaurant, with the new station being located a short distance to the east of it. The points which derailed the freight car no longer exist as Affoltern was downgraded from a full station to a “stop-point”. Freight traffic through Affoltern also ceased in 1995. All four burned houses were demolished after the fire, most of their former space is used for a soccer field and communal garden as of 2023.
The accident brought several improvements to the handling of large-scale emergencies, especially firefighting. First and foremost, after a media helicopter nearly collided with a rescue helicopter and several helicopters pushed smoke towards responders or blew firefighting-foam away from its intended place civilian helicopters are now banned from flying over or near the site of large-scale emergency situations.
Secondly, more and more fire departments are equipped with infrared cameras to both see the temperature of objects in a fire and see flames in heavily smoke-filled rooms. During the inferno firefighters had had no choice but to, after cooling down no longer burning train cars, eventually approach them to check the temperature. In some cases, as those involved claim, by eventually touching the surface with their hands.
Thirdly, the organization of large-scale emergency responses was improved. Nowadays responders would be sent not only to the site, but also to the dispatch center to support the standard crew in handling the increased workload. Similarly, responders heading to the site receive better routing and destination-information. During the 1994 accident ambulances were sent to the fire at the station while being intended to help the injured individuals several hundred meters away from the blaze, needlessly wasting precious time.
An accident like the one at Affoltern cannot be completely avoided, but with improvements to railway operation and maintenance along with constantly evolving equipment and strategies in emergency responses the accidents become less and less common and their consequences can be better controlled/limited. The fire department’s report on the fire at Affoltern alone has two full pages with nothing but bullet-points suggesting improvements to firefighting and emergency response strategies based on knowledge gained from the accident. And that is with a fire department that already was pretty much state of the art at the time of the accident, not one noticeably lagging behind.
_______________________________________________________________
A kind reader has started posting the installments on reddit for me, I cannot interact with you there but I will read the feedback and corrections. You can find the post right here.
