Before 42-year-old Jose Lara of Rifle died, he recorded a six-hour deposition detailing his work in the natural gas industry.

"If I would have known the damage those tanks would do to me, I would never have cleaned them," an emotional Lara said through a Spanish translator in front of a camera and room full of attorneys.

Dying from pancreatic and liver cancer, Lara described his job with Rain for Rent, a California-based company with a branch in Rifle.

His job was to power-wash waste water tanks for numerous natural gas drilling companies. For years, Lara said he was not supplied with a respirator, protective gear, or any warning of what he could be exposed to.

"The chemicals, the smell was so bad," Lara said. "Once I got out, I couldn't stop throwing up. I couldn't even talk."

Lara said he had no idea what he was being exposed to.

"[Rain for Rent] always talked about safety," Lara said. "But they never told me what was in those tanks."

Lara passed away three months after recording his deposition. OSHA would later cite and fine Rain for Rent with nine violations, six of them serious, for exposing Lara to a cyanide-like gas called hydrogen sulfide. The citation claim the company didn't properly protect, warn, and educate Lara about what he was being exposed to.

Both the industry and the Colorado Oil and Gas Conservation Commission, the state's agency meant to protect public health and regulate oil and gas, have denied the existence of high levels of hydrogen sulfide in Colorado. In 1997, the Colorado Department of Public Health and Environment wanted to monitor for hydrogen sulfide at oil and gas facilities after they were designated as confirmed sources of the deadly gas by the EPA.

The COGCC stepped in and told them not to, claiming there were no elevated levels in the state. The public health department listened, and tells us they haven't pursued any monitoring of hydrogen sulfide at oil and gas facilities since.

In 2010, Ryan Beaver's job was to monitor for hydrogen sulfide in the same kinds of tanks.

"I've seen the levels with my own eyes and I know what that stuff can do," Beaver said.

Beaver worked for On-Site Safety, a company contracted by Noble Energy in De Beque, Colorado. Outfitted with a monitoring device and gas mask, Beaver found multiple dangerous levels of hydrogen sulfide in just four months.

"We would open the lid, 'roll the tank,' and put our monitors inside," Beaver said.

Beaver found levels of hydrogen sulfide exceeding 2,000 parts per million, which is triple the lethal level. Beaver says he wasn't allowed to tell anyone, other than his supervisors, what the levels were.

"700 ppm will knock you out and kill you with the second breath," Beaver said. "I was getting three times that. It's a very well-kept secret."

One time, while workers were on site, Beaver's monitoring device read a level so high it maxed out his device.

"It just said 'error, error,' Beaver said. "I couldn't get anyone's attention, so I cracked my gas mask and yelled as loud as I could."

In the effort, Beaver was stricken with a near-lethal dose of hydrogen sulfide.

"My right eye felt like it was about to explode it hurt so bad," Beaver said. "I had a migraine for a week and a half, and I lost my voice for three days."

The attack happened just one day before Lara recorded his deposition.

The dangerous levels of hydrogen sulfide Beaver recorded in four months were never reported to the county or state, the Colorado Oil and Gas Conservation Commission says.

Beaver says he would enter the numbers from his field log book into a master log book with On-Site Safety, which presumably went to Noble Energy.

The industry has also discounted and fought air studies conducted in Western Colorado, some which turned up hydrogen sulfide readings.

"They won't let testing in, and they won't release what results they already have," Beaver said. "Of course they can say it's not true."

After NewsChannel 5's investigation, Noble Energy came forward and admitted they've seen hydrogen sulfide at a majority of their sites in Western Colorado.