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Yesterday, the U.S. Department of Transportation (USDOT) issued a final rule that establishes interim design standards aimed at improving the crashworthiness of tank cars carrying poison inhalation hazard (PIH) materials.

The rule mandates that tank cars carrying PIH materials, such as chlorine and anhydrous ammonia, feature thicker inner shells and/or outer jackets to improve puncture resistance in case of a side impact. In addition, the car's ends must be protected with a full head shield. To prevent a haz-mat release in a rollover accident, the cars also must feature stronger valves, top fittings and nozzles used for loading and unloading.

Under the new rule, the USDOT is imposing a maximum speed restriction of 50 mph on all loaded PIH tank cars. The department also is allowing for an increase in the gross weight of the cars to accommodate the enhanced safety measures.

To be applied to all PIH tank cars built on or after March 16, 2009, the standards will improve haz-mat tank car designs while the USDOT completes longer-term testing and research, and validates advanced tank-car designs for a more stringent performance-based standard, the USDOT said.

Tank-car owners must retire or replace PIH tank cars built before 1989 that feature non-normalized steel, which might not adequately resist fractures.