By TOM CALLIS
Tribune-Herald staff writer
Puna Geothermal Venture was back to normal operations Wednesday night after it was shut down that afternoon, causing a plume of steam to be released into the air.
The 38-megawatt power plant shutdown shortly before 4 p.m. when a transmission line between Kaumana and Pohoiki was tripped, said Curt Beck, energy services department manager with the Hawaii Electric Light Co.
The fault, which could have been caused by a tree branch, disconnected the line from the rest of the grid, leaving PGV with nowhere for its electricity to go.
The plant in Pohoiki automatically shutdown in response. With the plant offline, steam produced from the geothermal process was released as a safety measure.
About 20,000 customers lost power for about 15 minutes, Beck said. HELCO turned on its backup diesel generators to make up for the temporary loss of PGV.
The plant was operating again by midnight, said Mike Kaleikini, senior director of Hawaiian affairs for Ormat Technologies, PGV’s parent company.
The steam plume, visible to nearby residents, was not considered a health risk, though a few elevated readings of hydrogen sulfide were detected.
The gas is also a byproduct of the geothermal operation, and is contained during normal operations, according to plant operators.
Readings conducted by the Hawaii County Fire Department detected levels of the gas at 3 parts per million on Pohoiki Road between Hinalo Street and Leilani Avenue, said county Civil Defense Director Darryl Oliveira.
That area is downwind of the plant and is just outside its property line.
Another reading detected the gas at a level of 1 ppm on Pohoiki Road farther away from the plant, Oliveira said.
Other readings did not detect the gas.
Hydrogen sulfide is denser than air, and at least one of the two readings were recorded in a dip in the road, he said.
Oliveira said Civil Defense would not issue an evacuation order unless PGV could not contain the release and if sustained readings of at least 10 ppm were detected.
The release was not considered a health risk based on the levels recorded, he said.
Still, the county opened the Pahoa Community Center for residents concerned that it was not safe to stay home.
No one had shown up by the time it was closed after 7:30 p.m., Oliveira said.
“I guess it was more of a precautionary thing because initially we weren’t getting confirmation of readings on site,” he said.
PGV detected a peak reading of 19 parts per billion of hydrogen sulfide during the release. That translates to 0.019 ppm.
That reading was below the plant’s maximum permit level of 25 ppb (0.025 ppm) on an average hourly basis.
The gas becomes immediately dangerous to health at 100 ppm, according to the Occupational Safety and Health Administration.
Lower levels can irritate eyes and lungs, and OSHA limits workplace exposure to 20 ppm.
Up to 125,000 pounds of steam was released during the venting that lasted from 15 to 20 minutes, Kaleikini said.
The gas, which has an odor of rotten eggs, can also be smelled at low levels.
Some nearby residents reported smelling the offensive odor, Oliveira said.
Diane Thomas said the smell was strong at her home about a mile downwind from the plant.
“When it’s so bad that your nose is burning, it’s pretty serious,” she said.
Thomas said the release did cause her some concern but was told by officials that there was “nothing to worry about.”
The last time a similar release occurred was in November 2011.
A weather storm possibly tripped the plant offline then, Kaleikini said. That release was much smaller, with possibly about 10 percent as much steam vented, he said.
PGV removes about 98 percent of hydrogen sulfide in the steam, Kaleikini said.
The company will hold an informational meeting from 6-8 p.m. on March 28 at the Pahoa High and Intermediate School cafeteria to discuss noise surveys and ground water protection.
Kaleikini said Wednesday’s shutdown will also be added to the agenda.
Email Tom Callis at email@example.com.