 A train conveying flasks would be hauled by two locomotives, either Class 20 or Class 37, but Class 66 and Class 68 locomotives are increasingly being used; locomotives are used in pairs as a precaution in case one fails en route.Greenpeace protest that flasks in rail transit pose a hazard to passengers standing on platforms, although many tests performed by the Health and Safety Executive have proved that it is safe for passengers to stand on the platform while a flask passes by.The crashworthiness of the flask was demonstrated publicly when a British Rail Class 46 locomotive was forcibly driven into a derailed flask (containing water and steel rods in place of radioactive material) at ; the flask sustaining minimal superficial damage without compromising its integrity, while both the flatbed wagon carrying it and the locomotive were more-or-less destroyed.