Feb 18 - McClatchy-Tribune Regional News - Edmund H. Mahony, Dave Altimari and Josh Kovner The Hartford Courant, Conn.


Minutes before a deadly power plant explosion in Middletown, an employee monitoring natural gas levels discovered a dangerously high concentration and broadcast a frantic radio message urging workers to evacuate.

The warning came too late for five men who were killed and the dozens who were injured in the 11:17 a.m. blast on Feb. 7. Since then, a survivor, other plant workers, investigators and engineering experts have described in detail conditions at the plant that preceded the radio message -- conditions they believe may have contributed to an explosion that was heard and felt for miles.

In the hours leading to the explosion, the operators pumped enormous quantities of natural gas, in a series of purges, into a man-made depression behind the main plant structure, known as the power block building. Just yards away, welders worked in apparent contravention of generally accepted safety recommendations, a witness and investigators said.

The last of the series of gas purges was vented into a narrow space between two massive towers, the area where investigators believe the explosion occurred.

 Workers and investigators, who spoke on the condition they not be identified,said that, for most of the morning, the smell of natural gas was so pervasive inside the main building of the Kleen Energy Systems natural gas-fired power plant in Middletown that some workers complained of dizziness. Others, they said, expressed alarm that welding and other work was being done despite the odor of gas.

Worker concerns about what has been described as "saturation" levels of natural gas were passed along to two Keystone Construction and Maintenance Services employees who were monitoring gas detection meters for companies contracted to build the nearly completed plant. The smell of gas became widespread during a series of operations undertaken to blow out, or "purge," impurities from thousands of yards of pipes designed to carry gas to the plant's electricity-generating turbines.

For most of the morning, according to the survivor and an investigator, the men monitoring the meters told co-workers the gas level was within an acceptable safety range. Some workers disregarded the assurances and left the power block building.

Investigators have not been able to determine who broadcast the radio alarm that urged workers to leave because gas meter readings inside the plant had "spiked" or "pegged." One of the men monitoring the meters died in the explosion; the second was seriously injured.

Investigators said state police have recovered both meters. One was shattered, but investigators said they hope to recover memory chips that could allow them to determine the gas levels before the explosion.

So far, most attempts to identify the cause of the explosion have focused on the purging operation, in which thousands of cubic meters of natural gas was forced through thousands of yards of pipe and ultimately expelled through temporary vents along the south wall of the main power block building.

Investigators suspect that gas "pooled" just outside the building's three-story-high south wall, in particular within a sort of courtyard between the bases of two, 200-foot tall towers. Investigators believe the explosion occurred in the narrow courtyard between the towers. Airplane warning lights affixed to the top of the towers were blown off by the explosion.

At least three conditions at the plant have led investigators to suspect gas pooling. The temporary vent pipes discharged gas in a west-to-east direction, parallel to the ground, rather than upward, which could have hastened dissipation of the gas. Weather conditions, including low temperature, could have caused gas to settle. The gas also could have been captured in a bowl of sorts created by the wall of the plant, which sits on a site carved into the side of a rocky ridge. The plant is built on an abandoned feldspar mine.

"You'd be relying on natural ventilation," said a combustion engineer familiar with purging operations. "If the air flow is impacted, dilution is affected."

An on-site investigator speculated that, immediately before the explosion, the series of purges had turned the area outside the plant's south wall into a "giant swimming pool of natural gas."

"We are still trying to determine what was done or not done, but, frankly, the release of gas into that area doesn't make any sense," he said.

Workers said gas, if pooled outside the south wall, could have leaked into the main power block building through temporary wooden doors.

The state fire marshal's office, Middletown police and Middletown's fire marshal are still trying to determine if criminal charges will be filed in connection with the explosion. The local authorities have been joined in the investigation by the state police and at least three federal agencies, including the U.S. Chemical Safety and Hazard Investigation Board.

Public Safety Commissioner John Danaher has said the criminal investigation could take a month or more. The Kleen Energy plant has been declared a crime scene for the purposes of the investigation.

William Corvo, a partner in Kleen Energy Systems LLC, said Wednesday that he couldn't comment on the purging operation.

"I'm not yet in a position to answer any questions about the project, as the investigation is ongoing. The project continues to cooperate fully with the investigation," he said.

Keystone, in a statement, said, "Keystone will not be commenting on specifics, because the investigations are ongoing and we are cooperating. We were hired to provide labor support for start-up and commissioning. We continue to grieve the loss of our employees and support their families."

Purging became the suspected cause of the explosion within hours of the blast. That suspicion is reinforced by information provided by workers, witnesses and investigators, who say they also have questions about possible ignition sources just inside the south wall. They said those sources included welding and the operation of propane or diesel-fuel space heaters.

The purging of gas pipes had begun by 7 a.m. the morning of the explosion, workers and investigators have said. The purpose of the purges is to remove debris and gases other than natural gas from lines that feed the plant's two gas turbines and its steam turbine.

Sections of pipe were cleared in succession. During purging, natural gas is blown through gas lines with a force of up to 690 pounds per square inch, an enormous force hundreds of times more powerful than the pressure of gas delivered to residential buildings. Workers said the force of gas rushing through pipes during a purge creates an ear-shattering roar and is strong enough to convert tools mistakenly left inside the pipes into missiles.

A worker who observed the succession of purges and investigators said the multiple purge vents ran horizontally outside the south wall. A witness said the gases and debris being blown through the vents created a brownish cloud that he saw, periodically, hanging outside the south wall.

The last purge before the explosion was forced through pipes that vented into the courtyard area, an on-site investigator said. He said gas pressure used in the final purge was approximately 700 psi and released a "massive amount of gas" into the courtyard.

"The last 10 minutes of this purge created the optimum flammable mixture," he said.

Workers and investigators said there were multiple, potential ignition sources the morning of the purges, but they said most were inside the south wall. Two of the sources said welders were working on pipes at the east end of the south wall. An investigator said a diesel fuel-powered space heater was located by a large, temporary wooden door built into the south wall and opening into the courtyard area.

The investigator said doors opening through the south wall were not sealed.

Although the ignition source is unclear, investigators and others who examined the destruction, some immediately following the blast, said it was devastating.

Immediately following the blast, workers employed by the company hired to run the purging operations ran from a construction trailer where they had gathered into the power block building, carrying fire extinguishers and calling for colleagues thought to have been in the plant. They were blocked by fire.

The five men killed were working near the plant's gas turbines, an area close to where the south wall meets the courtyard. The five were flung through the enormous main power block building, through its shattered north wall and out the front of the building. One victim was found on an access road 70 yards from the blast site.

People who examined the destruction said steel girders were bent inward toward the center of the main power block building, suggesting that the blast occurred in the courtyard area. Structural surfaces in the courtyard that were not destroyed were charred.

One observer said trucks parked on the opposite side of the main power block building, 160 yards from the blast, were knocked off a road and into a ditch.

He said the blast moved an enormous cooling tower, nearly 200 yards long, a distance of 2 feet. The cooling tower was 80 yards from what is believed to have been the blast site.

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