BERTHOUD, Colo. -- Four workers were exposed in a chemical explosion Friday morning at the Carter Lake Water Filter Plant, located just southeast of Carter Lake in Larimer County.

A Berthoud Fire spokeswoman said it appears that while a truck was unloading chemicals into the water treatment plant, there was a chemical leak of some kind, causing a blast that buckled the roof and and blew out the windows and doors.

Four workers who were exposed were decontaminated. Two were sent to the hospital with minor respiratory injuries as a precaution, said Berthoud Fire spokeswoman Chloe McKinley.

Four firefighters were also decontaminated after working at the scene.

Authorities believe that it was some type of chemical reaction to chlorine that caused the explosion.

"There is speculation now that one chemical product may have been downloaded into the wrong container or a container which contained a product which reacted with the original," the Larimer County Sheriff's Office said.

Initially, just after the explosion was reported at 7:19 a.m., there was a small gas cloud hovering in the area, officials said. The chemical cloud dissipated quickly but fumes lingered for a bit, McKinley said.

All of the workers in the direct vicinity of the explosion were evacuated.

Residents near the area were cautioned to stay inside, keep their doors and windows closed and to turn off their air conditioners, swamp coolers and other types of ventilation systems.

The road that the plant is on -- County Road 8-E -- was closed until cleanup crews cleared the area.

Chlorine is used to disinfect water but is toxic as a gas and poses a serious risk of fire and explosion. In World War I it became the first chemical used as a weapon. Debra Graves of the Berthoud Fire District said it was not known how much chlorine leaked into the atmosphere.

Chlorine is normally stored as a liquid because can be very poisonous and potentially very deadly if inhaled in large quantities. Chlorine is an irritant to the lung and the lung will cease functioning if exposed to too much chlorine.

Crews entered the damaged building Friday afternoon and found a lot of spilled chemical product in inside. Hazmat crews must pump those chemicals to a holding tank for neutralization with other chemicals, Larimer County officials said.

But the process can very easily may take six hours if not through the evening and into Saturday morning.

Because cleanup is still ongoing residents who have left their homes will, as far as we know, not be allowed back through road blocks until all the chemicals have been cleaned up.

Those residents who have remained will be asked to stay in their homes through this period as well.

"As far as we know now, residents returning to their homes after being gone for the day will be allowed to proceed directly to their homes either to stay or, if they wish, to gather what items they want and to leave again for the evening," said Larimer County spokeswoman Eloise Campanella.

Water Supply Affected By Blast

The explosion has raised concerns about everything from notification to water quality.

"My only concerns are what's going to happen to our drinking water," said nearby resident Ron Gitlin. "Is there going to be any adverse effect... because that's the plant that feeds this whole area."

The Carter Lake Filtration plant is jointly owned by the Little Thompson and Central Weld County Water Districts. The plant can deliver up to 35 million gallons of treated water per day.

"The water is safe to drink," said Judy Dahl, the business manager of Little Thompson Water District. "The affected plant has been shut down, so all water being fed through the system is coming from a second plant still in operation."

But that second plant can only treat so much water, so mandatory restrictions have been imposed on the 59,000 customers of the two districts.

"They're being told that no outdoor watering is allowed, and to limit indoor use as much as possible until further notice," according to John Zadel, General Manager of the Central Weld County Water District.

Central Weld serves 50,000 customers in 8 communities including Platteville, Kersey, LaSalle, Gilcrest, the Tri-Town area and portions of Milliken, Greeley, Evans and the Aristrocrat subdivision north of Ft. Lupton.

Little Thompson serves 9,000 customers in a 300 square mile area from the foothills to 10 miles east of I-25... and from just south of Loveland to just north of Longmont.

It's not known how long the restrictions will be in place. Residents will notified when restrictions are lifted. If you have a questions about the water restrictions, call 970-352-1284.

Meanwhile, access is restricted to the south end of Carter Lake because of the incident. That means the South Shore and Carter Knolls campgrounds, the South Shore boat ramp, and the Saddle Bay Youth Area are closed. The north side of the lake is accessible but not past the Swim Beach. Boating is allowed on all areas of Carter Lake, although ramp access is limited to the north end of the lake.

Loveland hazardous materials crews, the Larimer County Sheriff's Department, and the Berthoud Fire Department all responded to the scene. The state Office of Emergency Management was monitoring the situation.

Mine blasting of a quarry that is in the area -- unrelated to the explosion -- had been planned for Friday morning. It was delayed a few hours but it went on after the area was cleared. A reverse 911 call was sent to nearby residents to alert them to the detonation so they wouldn't be alarmed by the noise.

Additional Resources:

Updates From Larimer County Emergency Team
Little Thompson Water District
Central Weld County Water District
Area Impacted By Water Restrictions (PDF File)