BACK in 1994 Swiss Federal Railways had two lucky escapes. The first was in March when a broken axle caused a train of petrol wagons to derail and catch fire at Zürich Affoltern. Five houses were burnt down and petrol leaking into sewers exploded, blasting manhole covers into the streets; one struck a woman who lost a leg. Three months later a train carrying chemicals derailed in Lausanne station, forcing evacuation of the surrounding area and closure of the station for several days. Again, there were no serious casualties, but the accidents cost SBB around SFr25m.

There had been another serious tank wagon derailment in 1991 at Stein-Säckingen, and SBB decided that the time had come to investigate ways of detecting derailed wagons. Working closely with suppliers and tank wagon users, it initiated a development programme for a detector that could be easily fitted to existing wagons. Tests covered a simple pneumatic device fitted to the buffer beam of a wagon, electronic sensors and coded pressure pulses along the brake pipe with a decoder on the loco. The choice for further trials settled on the pneumatic system as it needed no power supply, no communications link to the loco, and no special setting up before departure. Developed by Oerlikon-Knorr Eisenbahntechnik, it consists of a standard emergency brake valve, as fitted to passenger coaches, linked to a mass on a spring. When vertical accelerations dislodge the mass from its normal position, an emergency brake application is triggered.

Prototype equipment was fitted to a two-axle wagon, followed in September 1995 by trials on a four-axle wagon. This led to tests with 18 stone wagons owned by the Makies company. Each wagon had two detectors installed by Josef Meyer of Rheinfelden, and tests began in February 1996. After modifications to eliminate false alarms, the next step was to fit detectors to 25 Esso tank wagons, and since February this year they have been in regular service on the Antwerpen - Rümlang and Visp - Milano Treccate routes.

As OKE points out, the cost of equipment is always too high. The company estimates that series production would give a cost of around SFr3000 per wagon. This, it says, should be measured against the cost of accidents such as Zürich Affoltern. SBB has so far made no decision to install detectors on tank wagons.

In contrast, SBB has decided in the wake of the ICE disaster at Eschede in June to fit instability sensors to the bogies of its ICN tilting trains, now under construction; the sensors will activate an alarm in the driver’s cab. The question here is not simply cost, but reliability, as false alarms would prove expensive in terms of delays and disruption. o