July 8, 2013

expert reaction to train derailment and explosions in Quebec

A freight train carrying crude oil derailed and blew up in Quebec.

Gregory S. Patience, Professor of chemical engineering, Polytechnique Montréal, said:

“What is the cause of the explosion in Lac-Megantic?

“There are two types: the explosion (ie, an explosion with little power) and detonation (ie, an explosion can cause a lot of damage and occurs when the pressure front spreads faster than the speed sound). In the case of Lac-Mégantic obviously a detonation occurred. Witnesses said they heard seven shots (seven “booms”).

“For an explosion to occur, three elements must exist. It takes fuel (oil in this case), an oxidant (oxygen from the air) and a source of energy. Normally, the energy source is a spark, but it can also be a flame. In a car engine, for example, is the spark plug serves as a source of energy to create a controlled explosion.

“I saw a photograph of a train with a carriage alight before the derailment. If the technicians did not extinguish that flame, there was a derailment and petrol leaks in the presence of a flame, therefore all conditions to cause an explosion were met. Also, during the derailment, when metal rubs on asphalt or concrete, it makes sparks. This could be a source of energy for the explosion.

“However, a flame is not necessary to cause an explosion. If the temperature exceeds 200 degrees Celsius, and there’s oxygen and fuel, an explosion may occur. If the temperature reaches over 400 degrees, it can take only a second to explode. So, if the temperature is high enough, there is no need for an energy source (such as a flame) to cause detonation.

“But the explosion of Lac-Mégantic is surprising. In Saskatchewan last May, there was a train derailment with an oil spill of more than 575 barrels of oil and there was no explosion.”

Jean-Paul Lacoursière, Professor of chemical engineering, Université de Sherbrooke, said:

“Why did the emergency brake system not work? When the brakes of a locomotive work and if there is a driver inside, the driver holds his hand on a joystick to control the supply of fuel to the engine. If this lever is released, the motor stops and the brakes are activated automatically.

“When there is no driver, normally the brakes are activated automatically. In the chemical industry, it is a computer that manages security. For the transport of petrol in a train as here, it is a mechanical or electromechanical system that controls the automatic braking.

“We must now await the results of the investigation of the inspectors of the Office of Transport Security. They will view the data stored in the black box of the locomotive. The black box, such as in aircraft, is said to have resisted the explosion. The operating conditions of the machine (the train speed and the condition of the brakes, for example) are recorded. Inspectors can then use this information to reconstruct what happened.

“I was also surprised at the speed and scale of the explosion after the derailment. They say it is crude oil. There should have been an oil spill in the ditch without a fire. The consequence of this type of accident is usually pollution of water or soil. Here, we have a greater effect than a spill.

“However, if there is a car speeding down the slope and sparks are generated, it is possible that such an explosion occurs. Normally, this kind of explosion could be caused by propane (like for a BBQ) or butane transported under pressure.”

Rosa Galvez-Cloutier, Professor of civil engineering, Université Laval, said:

“When this type of accident occurs, it must initiate control and emergency measures to control and minimize the dispersion of hazardous substances in air, water and soil.

“In this case, we are talking about highly flammable petroleum products leaking from tanks, but also hydrocarbons which burn and are transported as smoke by the wind.

“We have to worry about the air quality. This smoke can be very toxic because they contain hydrocarbons that have not been completely burned. By-products of incomplete combustion are present in smoke (such as dioxins and furans) and are potentially carcinogenic. The mobile laboratory of the Ministry of Sustainable Development, Environment, Wildlife and Parks follows the air quality and should give some results to assess the situation.

“Until now, little has been said about the volume of dispersed oil and its future but we do not know the total volume, or the exact nature of spilled petroleum products into the river. There are several types of petroleum products and each product has a different density. Some float on the water surface while others sink to the bottom of the water.

“Obviously, if the oil has been spilled into the river, there will be a serious danger to the ecosystem mortality of animals, adverse effects on growth and reproduction of the species of animals affected and degradation of the quality water. Containment measures and collection of oil must be put in place to prevent severe damage to the environment.”