Six train cars that derailed on a Philadelphia bridge this week carried the same type of flammable crude that exploded in a small Canadian town, killing 47 people.

Although no oil spilled and no one was hurt, the CSX derailment Monday worried environmental activists, especially because it occurred in a densely-populated city. The trains derailed over the Schuylkill River, near the University of Pennsylvania, a highway and three hospitals.

“The cars are still there, twisted on the tracks,” said Iris Marie Bloom, director of the environmental group Protecting Our Waters. “As long as there’s toxic crude oil hanging over the Schuylkill River on a twisted bridge … there’s still danger.”

Environmentalists are not the only ones concerned after about a half-dozen oil train derailments in the past two years, several involving crude from the Bakken Shale in North Dakota, which they believe is proving especially combustible.

CSX — which transports Bakken crude from Chicago to several Mid-Atlantic refineries, including one in Philadelphia — is also studying the problem.

“Last summer’s tragedy in Canada opened eyes everywhere to the transportation of flammable materials, by all modes of transportation, but particularly right now there’s a focus on railroads,” spokesman Gary Sease said. “We understand how each incident that has occurred in the past 12 or 18 months affects public confidence.”

Last year, a runaway train hauling North Dakota crude derailed and exploded in Lac-Megantic, Quebec, incinerating much of the town and killing 47 people. The rail industry later adopted voluntary speed restrictions for trains hauling hazardous liquids. And last week, CSX officials and other oil and railroad executives met with Transportation Secretary Anthony Foxx, and agreed to make voluntary safety changes within 30 days.

They include plans to analyze the risks in major metropolitan areas, which could lead to route changes. However, Sease said that could mean longer trips on less sophisticated rail systems.

“We certainly are focused, and rightfully so, on the safety concerns here, but it almost obscures the fact that the new sources of oil and the ability to move them by rail to places where it’s needed is creating opportunities for energy independence, additional manufacturing, and additional job creation,” he said.

Fortunately, none of the cars that derailed in Philadelphia were breached. CSX plans to offload about 90,000 gallons of oil from the site in the next few days, weather permitting, and remove the five cars that remain there.

That doesn’t help Bloom sleep at night. She can hear the daily train whistles from her bed.

“The fact that this (latest) derailment happened right over the Schuylkill, right over the expressway, it’s pure luck that there wasn’t a fireball,” and people killed, she said. “We can’t count on that kind of luck in the future.”