The railcars that split open and burned in Tuesday's derailment near Clair, Sask., were Class 111, the same kind involved in the Lac-Mégantic disaster, CBC News has learned.
Rob Johnston, who is overseeing the federal Transportation Safety Board's investigation into the derailment, said seven of the cars travelling with the train were Class 111, a type that the board has said need safety upgrades.
Six of them were carrying hazardous products — hydrochloric acid, sodium hydroxide and petroleum distillates (a Varsol-type substance).
"The two that were carrying petroleum distillates did end up eventually releasing their products, and that was probably the source of the fire," Johnston said.
No one was hurt in the Saskatchewan derailment, in which 26 out of 100 cars went off the tracks, but officials noted the outcome could have been different if it had happened in a populated area.
Following the July 2013 Lac-Mégantic derailment, which resulted in 47 deaths and destroyed more than 30 buildings in the Quebec town, the TSB issued a report that found the Class 111 tank cars were outdated.
It said "enhanced protection standards must be put in place" for Class 111 tank cars. Damage to the Lac-Mégantic tank cars could have been reduced by enhanced safety features, the report said.
The TSB told CBC News it does not know whether the cars in Clair were given safety upgrades or not.
CN spokesman Jim Feeny told CBC News that the Class 111 tankers on the train that derailed are owned by independent shipping companies.
Feeny confirmed the tankers had not been upgraded to meet new safety recommendations, noting CN does not have the power to force the companies to upgrade the tankers.
"CN does not own these cars," Feeny told CBC News on Thursday.
He also pointed out that although they were the older model of tanker, it was OK for them to transport petroleum distillates.
"They are compliant with the current codes," Feeny said. "For the product that these cars were carrying, they were in full compliance."
He added CN would prefer to see the newer-model of tanker in use.
"We are in favour of an aggressive phase-out of the older DOT 111, but it will take time to do that," he added. "In the meantime we are required to accept them as our customers present them to us, so long as they are compliant with the existing codes."
According to Feeny, the cars in question number in the "tens of thousands" across the rail systems of North America.
"They are being replaced by upgraded or newer models, but it will take time," he said. "In the meantime, the products that they are carrying are essential for our everyday lives."