Article Archive
Confined Space
CSB report faults energy company, contractor for 2007 Colorado fatalities
Volume 25 Fall

Video simulation of 2007 confined space accidentLack of regulatory limits for bringing flammable materials into permit required confined spaced played a key role in a deadly 2007 fire at a Colorado hydroelectric plant that killed five workers and injured three, a report released by the Chemical Safety Board states.

At a August 25 press conference in Denver, CSB board member Mark Griffon said that regulatory standards established by the Occupational Health and Safety Administration pertaining to the use of flammables within confined spaces are inadequate.

"Other OSHA regulations on confined and enclosed spaces – for example in the maritime industry and other sectors – prohibit work in such confined spaces above a specific percentage of LEL (lower explosive limit), often ten percent," Griffon said.

The accident occurred in a water tunnel, or penstock, of a hydroelectric plant located 45 miles west of Denver. The penstock carries water from an upper reservoir to a lower one, driving power turbines.

Painting contractors were recoating a 1,530-foot steel portion of the 4,300-foot penstock when vapors from flammable solvent used to clean spraying equipment ignited. Flames quickly spread to additional buckets of the solvent, methyl ethyl ketone (MEK), and other combustible epoxy materials stored nearby.

Five of the 11 workers who entered the penstock were trapped behind the flames, cut off from an exit more than 1,400 feet away. The five retreated as deep into the penstock as physically possible, but were suffocated by the smoke within 45 minutes.

In 1993 OSHA issued a new regulatory standard for permit-required confined spaces in general industry. Research by CSB show that in the 17 years since there have been 53 serious confined space accident where flammable atmospheres led to fires or explosions. These accident caused 45 deaths and 54 injuries, most of them occurring in the last nine years.

OSHA's current confined space entry rule does not prohibit work entry into dangerous atmospheric environments where the concentration of flammable vapor exceeds 10 percent of the lower explosive limit, the CSB report states. As a result, CSB's three member board voted to recommend that OSHA strengthen its regulations to prohibit entry into a potentially dangerous atmosphere.

OSHA issued more than $1 million in penalties in March 2008 against the two major companies involved. Criminal indictments alleging violations of workplace safety and health rules leading to the deaths of the five workers were handed down by a federal grand jury in August 2009.

Aside from recommending that OSHA adopt industry wide LEL limits for confined space work, the CSB report challenged the selection of a painting contractor for the confined space project based on that contractor’s previous safety record. Also, the report criticizes the lack of preparation for possible emergencies during the confined space operation.

"If (the companies) had followed the current OSHA regulations that included requirements for planning, safe work conditions and conducting continuous air monitoring, this incident may have been avoided," Griffon said.

Donald Holmstrom, supervising the CSB investigation, said a standard hazard analysis prior to the confined space entry would have warned the companies as to the various problems. Both companies allowed flammable liquid to be introduced into a permit required confined space without taking proper precautions.

"One of the things I’ll emphasize is that there are several known non-flammable solvents that could have been used in this incident to substitute for methyl ethyl ketone," Holmstrom said. "In other words, if they needed to bring a solvent into a confined space, it could have been a non-flammable, safer alternative."

Holmstrom is also lead investigator into the explosion and fire that destroyed the Deepwater Horizon offshore drilling rig in April, triggering the Gulf oil spill.


As explained in a 15-minute video released by the CSB and based on their investigation, the hydroelectric plant in question is located in a remote, mountainous area. A 4,000 foot tunnel, known in the industry as a penstock, carries water between reservoirs at differing elevations. At the lowest level, where water flowed through large turbines to generate electricity, the penstock was only slightly inclined for a distance of 3,123 feet.

Beyond that, the penstock rose sharply at a 55 degree angle too steep to traverse without climbing equipment.

According to the CSB report, many hydroelectric plants have steel penstocks that have not been relined or recoated for many years. In North America, estimates suggest that three million feet of in-service penstocks exist. Interior coatings and linings are required to maintain the structural integrity and serviceability of penstocks to prevent corrosion and provide water tightness. 

Over the years, deterioration in the penstock’s epoxy lining at the hydroelectric plant in question had been noted. In 2007, the owners contracted with an industrial painting company to recoat a 1,560 feet long steel-lined section of the penstock near the power plant and the lower reservoir. Work began at the site in September.

Even before the operation began, the stage was set for disaster, Griffon said. The contractor chosen did not have an acceptable safety record based on the plant owner’s own evaluation standard.

The plant owners "not only did not adequately plan for the operation, but it selected the painting contractor with the lowest possible safety rating among the bidders, and it did so mostly on the basis of cost – it was the lowest bid," Griffon said.

The CSB investigation found that the plant owners hoped to compensate for the painting contractors safety record by closely supervising the contract work, he said. That oversight proved inadequate, even when the company learned of safety issues during the initial penstock work, Griffon said.

Even with regard to existing OSHA regulations regarding confined space entry, the project undertaken near Georgetown was deficient, the CSB report states. The plant owners did not implement a permit-required confined space program or issue permits for its personnel who entered the penstock for inspection or maintenance.

A penstock is a unique confined space that is difficult to enter and exit, the video states. Before the project began, a door was cut into the lower section of the 12-foot diameter penstock to provide access for workers and their equipment. Save for an entry port at the highest elevation of the penstock, the door was the only point of entry and egress for workers.

On the morning of the accident, contract workers prepared to begin the coating operation by bringing about 10 gallons of MEK into the penstock. The CSB investigation found that managers for both companies involved were aware of the plan to use solvent to clean the epoxy sprayer and other equipment while inside the penstock, Holmstrom said. Yet neither company performed a hazard evaluation of the epoxy coating work.

"As a result, the companies failed to identify serious safety hazards involving the use of flammable liquids in a confined space," Holmstrom said.

Existing good practice guidelines recommend against working in any confined space where the concentration of flammable vapor exceeds a specific low percentage of the lower explosive limit (LEL), the lowest concentration of a flammable vapor in air that can burn when ignited, the CSB report states.

Overseas regulations, as well as certain OSHA standards, including the OSHA standard for shipyards, prohibit work inside a confined space if the atmosphere exceeds 10 percent of the lower explosive limit. However, with regard to OSHA’s general industry standards, which regulates more than four million permit required confined spaces across the county, no such safety limit exists.


Shortly after 1 p.m., 11 workers began coating a section of wall located more than 1,400 feet inside the penstock. To apply the new two-part epoxy coating, workers used a specialized sprayer. Base and hardener were mixed before being sprayed onto the walls. However, the workers immediately encountered problems. The epoxy was not adhering evenly to the surface.

The workers flushed the hoses and spray wands with MEK each time a problem arose. Despite their efforts, the problem persisted. A foreman for the painting contractor decided to clean and remove the sprayer from the penstock. The crew began cleaning out the hoses and equipment, again using MEK.

More of the solvent was brought into the penstock. Some workers noticed the strong odor of MEK as the vapor spread through the work area, the report states.

At approximately 2 p.m., the vapor ignited. The most likely ignition source was static electricity inside one of the spraying machine hoppers, the report states. A flash fire erupted. Burning solvent burst from a hopper onto a nearby worker, setting his sleeve on fire. The flames spread quickly, engulfing the open buckets of MEK nearby.

Five workers were blocked from escaping the penstock by the intense fire. Although the trapped workers shouted for fire extinguishers, none were available inside the penstock. Workers on the other side of the burning equipment ran the 1,400 feet to the entrance to locate extinguishers. The control room operator was notified to call 911.

The trapped workers, in contact with the outside by radio, fled deeper into the penstock to escape the smoke. Their colleague, now armed with extinguishers, repeated attempted to fire the fire, but were forced to turn back because of intense heat and thick smoke.

At 2:11 p.m., county emergency personnel arrived, but had not been informed as to the hazardous conditions inside the penstock.

"The responders were not equipped or trained to attempt such a technically demanding rescue," the video states.

An interview with Capt. Steve Aseltine, division chief for training with Denver's West Metro Fire Rescue district is included in the CSB video. Aseltine and his team later responded to the confined space accident.

"A permit required confined space is any area that can have an atmosphere that is immediately dangerous to life or health," Aseltine said. "You are required to have a rescue team on site and professionals there to help you in a permit required confined space. Most times that we see, people just blow that off. Unfortunately, those are the people that don't get to go home."

By 2:25 p.m., the trapped workers were instructed to move even deeper into the mountain. When they reached the point where the penstock steeply rose, the workers could retreat no further. By radio, they told responders that they were struggling to breath. Responders using an all terrain vehicle inside the penstock could not advance further than 200 feet from the entrance because of the smoke.

Responders then drove up a winding road than rose more than 1,000 feet to the upper reservoir. At 3:15 p.m., they lowered air bottles and respirators through a small hatch, hoping to reach the trapped workers below.

At 3:40 p.m., the specialized rescue unit arrived from Denver. Thirty minutes later a specialized mine rescue unit arrived. However, the five trapped workers died at least an hour earlier, the report states. The following day, responders found their bodies near the bottles of air lowered from above.

The amount of time between ignition and the deaths of the workers is significant, the CSB video states.

"The fact that there was 45 minutes before the last radio communications tells us that there probably would have been enough time had an emergency responding group been there and been prepared to handle the chemicals inside to potentially put it out and rescue the individuals," CSB investigator Cheryl MacKenzie said.


Beside OSHA, the CSB made recommendations to nine other entities, including the state governor's office and the Colorado Public Utilities Commission. The governor was asked to implement an accredited firefighter certification program for technical rescue with specialty areas including confined space rescue. The Colorado PUC was asked to require regulated utilities to adopt provisions for selecting contractors based on safety performance measures and qualifications.

The PUC was also asked to investigate all incidents resulting in death, serious injury or significant property damage and submit and make public written findings and recommendations within one year of the accident.

CSB investigators and board members cited difficulties encountered in the investigation resulting from efforts by the companies involved to impede the investigation and prevent the release of the investigation report.

Citing a formal letter of admonishment sent to the chief executive officer of the power company earlier in the week, CSB board member William Wark said the lack of cooperation and efforts to impede the investigation was unprecedented.

"Mr. Griffon and I join our chairman in criticizing these actions in the strongest terms," Wark said.

The letter, signed by CSB Chairperson Rafael Moure-Eraso, states the company did not fully comply with CSB requests for documents or answers to questions in formal interrogatories. This required the CSB to seek assistance from the U.S. Attorney’s office in Denver, resulting in delays to the investigation and additional costs to taxpayers. In May, the power plant owner went to federal court seeking to block release of the CSB report and the safety video. The court sided with the CSB in favor of release.

An attorney for the plant owners then released the draft report to the Denver Post only days before a vote by the CSB board on the final draft.

In accordance with CSB review protocols, the owner was given an advanced draft copy of the report last April for review for accuracy and for confidential business information. A CSB press release states the company never responded, but in August, contrary to the conditions of confidentiality attached to their receiving this preliminary copy, released it to a news organization.

An attorney for the power company quoted in the Denver Post denied the company was uncooperative with the agency. He charged that the CSB sought to influence the criminal case against the owners for violating federal workplace standards by releasing the report closer to the trial date.

That trial is not expected to begin until next year, the newspaper states.

He further stated that the company was unaware that the contractor went inside the penstock with an unsafe amount of chemicals. The newspaper quoted an attorney for the coating contractor stating that the company disagrees with the CSB report.

No Escape: Dangers of Confined Spaces- To access the CSB video "No Escape: Dangers of Confined Spaces," click HERE.

- To access the CSB final report regarding the October 2007 death of five industrial painting contractors deep inside a hydroelectric plant tunnel, click HERE.

- To access the letter by CSB chairperson Rafael Moure-Eraso regarding lack of cooperation in the investigation of the October 2007 deaths near Georgetown, CO, click HERE.


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