By Adam Federman   Utne Reader (This post originally appeared at Earth Island Journal.)

“…the oil has to travel long distances, in some cases thousands of miles, and is subject to fluctuations in temperature and pressure, a factor that Smith says can contribute to its volatility. As temperatures rise, the oil warms and expands. As the rail cars move and shake, volatile compounds like propane and butane can separate from the oil and rise to the surface, collecting in the headspace above the liquid petroleum. A small puncture, leak, or derailment accompanied by a static charge or spark can set off an explosion.”

http://www.utne.com/environment/lac-megantic-disaster-zb0z1405zjhar.aspx#axzz32Y6IzhAw