Firefighters are flooding the car with water in the hope the propane will rise to the top of the car and burn off more quickly.
Shortly after 5 p.m. Monday, CN tried for the second time to use explosives to puncture the derailed cars to help burn off the propane, but shortly after 7 p.m., it found one tank car still contained almost 57,000 litres of propane.
CN intended to start a third control burn, but when officials discovered the propane tank car was flaring just before 9 p.m., officials decided to pump water into the tank to hasten the burn-off.
Fire crews began pouring water into the tank before 7 a.m. Tuesday.
CN said it will not predict when 126 residents can move back into their homes near the derailment site near Gainford, 80 kilometres west of Edmonton.
CN has said the 134-car train was travelling to Vancouver from Edmonton at a normal speed of 35 km/h when 13 cars left the tracks.
The Yellowhead Highway — the main east-west corridor in northern Alberta, connecting Edmonton with Jasper — remained closed at scene Tuesday.