At a chemical site, a braking problem on an incoming rail convoy containing liquid sulphur caused derailment of the cars and their collision with other cars parked on the track. A rail handling subcontractor was assigned to process 11 railcars filled with liquid sulphur through to the transfer station. The traction team (handling manager + rail conductor) pulled the convoy southward with a shunting locomotive before pushing the convoy back onto track no. 9 towards the site. Prior to crossing a road, the conductor actuated the train brake to decelerate but this brake was inoperable. He immediately pushed the locomotive’s emergency stop button; however, brakes on the locomotive failed due to the cumulative weight of the cars. Technicians jumped from the convoy before it collided with 5 empty cars, used to transport carbon disulphide (CS2), parked on track 14 beyond the transfer station. The tangle of cars was dragged onto track 20 and smashed into a bumper installed at the end of the track. One car containing sulphur and two others loaded with CS2 derailed. A 300-tonne crane was required to remove one of the CS2 cars, which was lying sideways below the track damaged by the accident, along with 4 other cars. Despite the pileup, no chemical product leaked. The facility’s internal emergency plan was launched; it was lifted 6½ hours later. This accident was caused by human error, since no equipment defect could be identified. The conductor had failed to verify that the caboose cars were connected to the compressed air circuit fed by the shunting locomotive, as this air supply ensured brake operability: draining the compressed air tanks in these cars had rendered the braking system inoperable. Moreover, the conductor had not performed a braking test before initiating convoy movement. Within the scope of experience feedback, the rail handling firm committed to: enhancing employee awareness of site-related risks; upgrading technician supervision, notably in verifying compliance with safety instructions; deploying automated shunting locomotives programmed to control the braking system; revising the procedure for on-site convoy movement; and improving network infrastructure by installing sand pits at the end of each track length, along with a runaway track.