Leaking Tank Car

Question:  Ok, so today on NS, NS 16N had a tank car venting Carbon Dioxide and they stopped the train and couldn't stop the leak.   But the Chief dispatcher in Greentree, PA, ran the train anyways was this the proper thing to do?

Answer:  Yes.  I’ll assume the tank car was transporting carbon dioxide, CO2, in either gas (UN1013) or liquid (UN2187) form.  Both are hazard class 2.2, non-flammable, non toxic gases.  While CO2 is an asphyxiant gas, and can be harmful in high density, it is generally a minor, manageable hazard in small quantities diluted in the atmosphere (plants and trees exhale CO2).  Once the train crew verified the leak was indeed CO2 and in relatively small volumes, federal rail and HAZMAT transportation regulations (from which railroad HAZMAT rules are derived) permit the continued movement of HAZMAT shipments in order to further reduce or eliminate the threat to public safety (in this case, either get it to its final destination where it can be unloaded, or taken to a point where the CO2 can be safely transferred to another tank car).  The leaking car would have to have buffer cars between it and the engines.  NS likely has a procedure in place whereby the chief dispatcher is empowered with the authority to authorize such a movement (I’m sure only after consulting with specific written railroad policy and/or consulting with folks at HQ).  Had the leak involved a significantly more hazardous material, or had it been a high volume leak, the railroad’s response would have been completely different.