Citizen activists in the natural gas drilling hotspot of western Garfield County, Colo., apparently caught Halliburton employees on tape working in and around a cloud of hydraulic fracturing sand emanating from tanker trucks near a Williams natural gas well pad in Parachute last week.

Video (below) shot by Dave Devanney of Battlement Concerned Citizens appears to show Halliburton workers without respirators, although observers say breathing fracking sand can be very dangerous because it contains silica, according to a story in the Grand Junction Daily Sentinel.

The Sentinel story quotes a Silt Mesa resident and former contract worker named Carl Mc Williams, who claims he was sickened by hydrogen sulfide while working on a Noble Energy gas well. Noble now acknowledges it is finding hydrogen sulfide in the majority of its gas wells on the nearby Piceance Basin, although the potentially deadly chemical was previously thought to be rare.

“They have been telling us all along that there is no H2S [hydrogen sulfide] in this area,” Devanney wrote in an email to members in which he also included a link to his Halliburton video.

David Neslin, director of the Colorado Oil and Gas Conservation Commission, told the Sentinel the state is investigating the Noble hydrogen sulfide situation. Both Halliburton and Williams told the paper they’re looking into the fracking sand emissions.

The contractor Mc Williams worked for when he claims he was sickened in 2009 was fined $2,000 by the Occupational Safety and Health Administration. A Noble spokesman acknowledged the company has been regularly encountering the gas ever since then, using “biocides and other methods to eliminate it.”

“It’s a concern, but it’s not one that we’re inexperienced in dealing with,” a Noble spokesman told the Sentinel.