A strong odor that carried through the air Thursday in Robstown was not the result of a ruptured gas pipeline, Robstown Utility Systems superintendent Roy Gutierrez said, but due to improper levels of a chemical meant to serve as a warning agent for residents.

The problem was due to an imbalance of methanethiol, also known as methyl mercaptan, and the city's natural gas supply. Methanethiol is often mixed with natural gas, which is odorless, in order to provide customers with a distinct odor that is similar to rotten eggs to warn of a potential gas leak in or near their homes, Gutierrez said.

"It's doing what it is supposed to do," he said.

The chemical is a natural occurring substance often found in the blood, brain and other animal and plant tissue. It is not considered hazardous to humans, Gutierrez said.

"It's intended to alert you, but it's not harmful," he said.

Because low levels of methanethiol had managed to become concentrated in the natural gas pipelines around the city, the smell was much stronger than it usually would have been under normal circumstances.

"Whereas before normally you wouldn't smell that, now you would," Gutierrez said.

Robstown resident Joe Avalos said the odor was very noticeable and made it hard for he and his wife to sleep, partly because they were not sure if there was a leak in their home.

"I was afraid to go to sleep because I didn't know if we were going to die," Avalos said, adding that he took precautions, such as turning off his stove and air conditioning, to lessen the smell.

"It was crazy," he said.

The addition of more methanethiol to help rebalance the levels with the natural gas had begun to diffuse the odor as of Friday afternoon, Gutierrez said.

Robstown Utility Systems director finance Roland Ramos said the department received numerous calls from residents throughout the city on Thursday and Friday, with each instance being treated as a gas leak.

Some leaks were discovered in a few of the homes crews visited, but more than likely had existed prior to the methanethiol imbalance, Ramos said.

The situation just made those leaks more evident, he added.

City crews are continuing to monitor the situation as of Monday.