A train derailed at a rail yard in Green Tree early Thursday morning, causing a by-product from Marcellus Shale drilling to leak.

Firefighters said a valve on a train car broke and released the propane mix into the air.

"I woke up around 5 a.m. and I smelled gas. I didn't know where it was coming from," said resident Patricia Wagner.

"My wife said she smelled almost like a gas smell in our basement," Jim Vincenti said.

Officials went door-to-door alerting residents on Hawthorne Street and tested the air to make sure everyone was safe.

The released chemicals were a by-product from Macellus Shale drilling. Residents said this is the second time this year that an incident like this one has happened.

"All of our lives are at stake here. There's a health concern here. It's frightening," said Wagner.

Allegheny County assistant emergency management chief, Alvin Henderson, said the leak didn’t put anyone at risk because of the swift reaction from emergency officials.

"Anytime you have a hazardous incident with an active leak it could have been dangerous. The fire department took all of the right precautions right away," Henderson said.

Residents said they plan on going to Green Tree borough officials to discuss the increased train traffic from Marcellus Shale drilling to see if additional precautions can be taken.