One person was killed and four others injured after a gas leak at a well in Guernsey County.

Officials said the men were working on a gas rig, preparing to cap the well, when they were overtaken by a poisonous hydrogen-sulfide gas mixture.

The accident happened near Londonderry at the intersection of Skull Fork Road and Ginger Road. A spokesperson for Antrim Volunteer Fire Department said one man went down and the others tried to rescue him.

Three victims were transported to Cambridge Hospital for treatment. One person was transported by medical helicopter to another Ohio hospital.

Officials said one of the victims is in critical condition.

The gas the men encountered is commonly referred to as "poison gas" or "sour gas" and is common in natural gas drilling. The men were wearing the proper meters to check for gas, officials said.

"It happens all over. It's something they're trained to deal with but, sometimes it happens so fast that their protective clothing doesn't warn them quick enough and they're unable to deal with it," said Antrim Volunteer Fire Department Chief Don Warnock.

The men are employed for Chipco Oil and Gas Well Services. Company representatives were at the site Thursday but had no comment.

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