PITTSBURG -- State officials are investigating an industrial accident at K2 Pure Solutions involving the release of a small amount of chlorine gas that sent a worker from another company to the hospital a few weeks ago.

It's the second time in three months there has been a release of chlorine gas at the site. The K2 plant was shut down after an equipment malfunction in early December led to the release of a small amount of chlorine gas in its liquefaction unit. No one was hurt in that incident, and it was later determined that a failure in heat-exchanging equipment caused the leak.

The liquefaction unit, which provides Dow Chemical's Pittsburg operations with chlorine, is expected to open in the next couple of weeks after repairs are completed. The main section of the plant that produces bleach products for other customers reopened in early January after repairs were made.

The most recent incident was on Feb. 8, said Peter Melton, a spokesman for the state Division of Occupational Safety & Health, known as Cal/OSHA. He did not know where the leak occurred on the K2 Pure property.

"This is a dual-employer situation," said Melton, adding that the three employees who were exposed to the chlorine gas work for the Benicia office of Corey Delta Constructors, which provides construction and maintenance services to industrial facilities in the western United States.

One of the Corey Delta employees, a 34-year-old male, was taken to the hospital for more than 24 hours and later released, Melton said.

Jake Witkowski, a safety manager at Corey Delta, could not be reached for comment.

"We had a small incident. One guy was affected. He ended up in observation until he got released," said Leon Zaal, vice president and general manager of K2's Pittsburg plant.

In September 2011, Toronto-based K2 opened its Pittsburg plant on a 13-acre parcel on Dow's Pittsburg property through a partnership between the two companies. The K2 plant's liquefaction unit provides Dow's Pittsburg operations with chlorine to make a variety of agricultural products, including pesticides.

The closure of the liquefaction plant since December has not impacted operations at Dow.

"We are able to get raw materials from out of state and are able to keep running," Dow spokesman Randy Fischback said.

Contact Eve Mitchell at 925-779-7189. Follow her at Twitter.com/EastCounty_Girl.