Hercules' $145 million missile-manufacturing project, rejected by Salt Lake County planners last month, was unanimously approved by the County Commission Monday morning.

The commission's decision was the final defeat for Magna area residents who opposed the project, fearing an accidental explosion could destroy homes surrounding the plant. Surveyors were to begin preparing ground Monday afternoon for construction of the project, which will expand facilities already at the plant, Hercules officials said.The company will manufacture Titan IV and Delta II rocket motors for the U.S. government.

Commissioners made no comment as they voted to overrule the Planning Commission, which rejected the project on a tie vote. The decision came after a two-hour hearing attended by several hundred people.

Hercules officials said the project will generate $2 billion over the next 10 years and add five times that to the local economy. But because of delays in approval from the county, the company may lose money by missing its first deadlines.

"We have a due-date to produce those first rocket motors," said Jack DeMann, Hercules public affairs director. "We've run out of wiggle-room. We need some breaks with the weather."

Construction is expected to take 20 months, he said.

Most of the people at Monday's hearing favored the expansion. Opponents, however, were upset that many of the people were Hercules employees who admitted they were being paid by the company to appear at the hearing. Company officials said all employees at the meeting live in Magna.

Dan Jones, president of Dan Jones and Associates, said his company conducted an opinion poll for Hercules officials showing that 72 percent of residents countywide favored the expansion, while only 15 were opposed. The survey included 400 interviews and has an error factor of plus or minus 5 percent.

Jones also surveyed Magna residents alone and found that 72 percent of them also favored the project.

Opponents of the project urged commissioners to listen to their planners and reject the expansion.

"You're listening to a stacked meeting," said Chick Paris, president of the Magna Water Co. "What I'm looking for is the health, welfare and safety of the community."

Other Magna residents, most of whom were members of one of the area's two community councils, said the expansion would put their lives at risk.

"Human error, mechanical failure and acts of God are inevitable," said Marlene Norcross, vice president of the Magna Area Council.

But supporters in attendance included Craig Moody, chairman of the state Republican Party, a representative from the office of Rep. Howard Nielson, R-Utah, and numerous business leaders from throughout the county.

The company's plans may have suffered most during recent weeks from an unrelated accidental explosion in Henderson, Nev. Critics questioned what a similar accident would do to nearby residents in the unincorporated Magna area.

Hercules officials felt they had provided evidence that a similar accident could not occur at their rocket-manufacturing plant. But two planning commissioners and many local residents disagreed.

In an indirect way, the delays may have been caused by company officials who threatened to leave Utah last year unless the county stopped developers from building houses close to the plant. The threat of an accidental explosion was raising the company's insurance rates, they said, noting that houses should not be built within a 1.5-mile buffer zone around the plant.

When the company announced plans to expand, critics said the expansion would push the buffer zone out farther. Hercules officials denied those claims, saying they were using pits and other construction methods to limit the effects of a blast.

County officials signed an agreement with West Valley City last year after Hercules threatened to leave the state. The agreement called for West Valley City to annex half of Hercules and to buy $10 million worth of undeveloped land in the danger zone. Hercules also agreed to buy about $8 million worth of land.

Magna residents tried unsuccessfully to stop the annexation, claiming it would rob them of the ability to become a city some day.

The expansion is planned for the unincorporated county and will make up for some of the tax money the county lost when West Valley City annexed half of the plant, company officials said.