“ As we said in that case: 'At best, appliances standardized in Commission regulations represent the minimum of safety equipment, and there is no prohibition of additional safety appliances.' 350 U.S., at 324, 76 S.Ct., at 391. ”

“ We held in Shields that if a safety appliance is provided by the railroad or the makers of the car and used by the railroad as an appliance necessary for the use of the car, it must be safe.
One man is dead and another is crippled for life because the dome lid on the tank car furnished by the respondents was defective. The dome lid was provided by the respondents as a safety appliance ”