SACRAMENTO, Calif. — Engineers at the Consumer Product Safety Commission privately warned nail gun makers in 2002 that their industry's efforts to reduce the increasing number of people shooting themselves and others with the tools wouldn't really work, newly disclosed federal documents show.

But the engineers' views, and their calls for further study of the popular power tool's safety features, were never addressed or disclosed to U.S. consumers.

Thousands of professional carpenters and do-it-yourselfers continued to buy or rent nail guns at giant hardware stores across the country during the housing boom with predictable consequences.

The number of people sent to hospitals with hand, foot, knee and head injuries caused by air-powered nail guns surged to 42,000 in 2005, up sharply from 12,982 people in 2000, federal hospital injury data shows.

Commission engineer Caroleene Paul, who wrote the 14-page report and forwarded it to the agency's Office of Hazard Identification and Reduction, did not respond to requests for comment. The Sacramento Bee obtained a copy of the report from the consumer protection agency under the Freedom of Information Act, only after threatening legal action.

Based on nail gun tests and interviews with injury victims, the report was among 250 pages of internal commission documents about nail gun injuries and trends between 2002 and 2007.

Other documents included details of a nail gun death in 2006, four years after Paul's report.

Laborer Juan A. Delgado, then 41, shot himself in the head two hours after buying a Duo-Fast nail gun for a fence job at a Houston Home Depot. He died at a Houston hospital five days later.

Delgado left behind a wife and three children in Coahuila, Mexico, and a sister and brother in Fort Worth, Texas, a Harris County medical examiner's report said.

Duke University researcher Hester Lipscomb, who has studied nail gun injuries for a decade, said she was disturbed by the consumer agency's inertia after the 2002 report, because its engineers and the nail gun industry group clearly were aware that tools equipped with automatic "contact-trip" firing systems were hurting and killing people.

"It would be interesting to know how many injuries and deaths, among both workers and consumers, could have been prevented," Lipscomb said.

When the Consumer Product Safety Commission first expressed concern about the increasing number of nail gun injuries in 1998, the Illinois-based International Staple, Nail and Tool Association, or ISANTA, produced a nail gun safety video to appease the government agency. The video can be downloaded from the groups' web site.

ISANTA also revised its voluntary nail gun standard to suggest, though not mandate, a safer firing system for larger nail guns. Nail gun makers could meet the standard while still shipping their products with a kit in the box that allowed users to convert their tools back to the more dangerous firing system.

After studying ISANTA's efforts, testing nine nail guns and interviewing the injury victims, the safety commission's engineering team said those efforts fell short of what was truly needed to lower the number of injuries.

In her May 23 2002 report, Paul stated that ISANTA's safety video and revised standard would not actually reduce the genuine risks for people using the potentially lethal power tools.

"Staff believes that a video is insufficient to address the injuries and that revisions to the voluntary standard that would include performance requirements to address the injuries are needed," Paul wrote. "Performance requirements," in engineer-speak, means design changes to the various nail guns' firing and safety systems so that fewer people would be hurt using the tools.

Paul's report also called for a probe into nail guns' propensity to recoil and double-fire nails — a common occurrence that has hurt thousands of people.

Double fires are dangerous, Paul wrote, because a second nail fired on top of the first can ricochet off the nail's head and cause injuries or miss the intended target completely to "strike a body part or victim."

The medical examiner's report's into Delgado's death and the safety commission itself noted that his tool often recoiled or "double tapped" when fired horizontally, sometimes causing double fires. Investigators were baffled by his death. There were no direct witnesses, but they believe he may have double fired a nail that ricocheted and hit a nearby metal dumpster before it then zoomed back at him, slamming into the back of his head.

The Sacramento Bee published an investigation into the hazards of nail guns this spring, focusing on the perils of the widely used automatic firing system on the tools known as the contract trip trigger.

Contact trip nail guns fire a nail each time users pull the tool's trigger and the work contact piece makes contact with an object — including the user's own body, or that of a co-worker or passerby. The two steps can happen in any order. Though instructed not to carry the tool by the trigger, many users do because its center of gravity almost requires it to comfortably carry it.

The Bee reported that a safer firing system known as the sequential trigger exists and is used on some nail guns. Such nail guns fire only when the work piece is first pressed against a target, and then the trigger is pulled in that sequence and just one nail can be fired. The work piece and trigger must both be released before the tool will fire again.

Though Paul's report was not made public, Paul sent a copy to ISANTA's Chicago attorney Jed R. Mandel, acknowledging the industry group's interest in promoting tool safety but adding that she hoped "safe product design will continue to be a priority in pursuing that interest."

Neither ISANTA nor Mandel returned messages seeking their comments.