Former letter carrier Michael Bigler remembers the terrified screams of his co-workers 20 years ago when a disgruntled postal worker went on a shooting rampage that would come to define the term "going postal."

On Aug. 20, 1986, Patrick Henry Sherrill tucked two .45-caliber pistols into his postal satchel, locked the doors of a post office in this Oklahoma City suburb and systematically killed 14 people, then committed suicide.

"The screams hurt me emotionally more than the bullet did when it hit my back," said Bigler, one of six people wounded in the attack. "They screamed in terror when they screamed their last breath. He wanted to slaughter us all."

In the two decades since Sherill's rampage, the U.S. Postal Service has tried to prevent worker violence, but there have been other attacks. Nearly 50 people have died in post office violence since the 1980s, including six postal workers who were shot in January at a mail-processing center in Santa Barbara, Calif., by a former postal worker who killed herself.

The massacre at Edmond's main post office, about 12 miles north of Oklahoma City, was the deadliest of the attacks and put a spotlight on the tensions faced by postal workers.

"Carrying mail, in and of itself, can be a stressful job," said Steve Riggs, president of the Oklahoma City branch of the National Association of Letter Carriers. Bad weather, irritable customers, heavy mail loads and unrealistic expectations from supervisors create on-the-job tension.

"We have disagreements," Riggs said.

Bigler said there were reports before the shootings that management was trying to fire Sherrill for poor work performance.

Afterward, the Postal Service examined management's relationship with letter carriers and postal clerks and tried "to take a deeper look at everything that we do — and everything that we don't do," said Larry Flener, manager of consumer affairs for the Postal Service in Oklahoma.

In 1998, the Postal Service created an independent commission to assess workplace violence and make postal facilities safe and secure.

The commission found that postal workers were no more likely to resort to workplace violence than workers in other jobs. It found 0.26 workplace homicides per 100,000 postal workers from 1992 to 1998. By comparison the rate was 2.10 per 100,000 for retail workers, 1.66 in public administration, 1.32 for transportation and 0.50 for private delivery services.

"Violence is purely unpredictable. It is a part of our society," Flener said. "Terms 'going postal' and those things have taken on a life that is totally unfair."

"It only serves to further the injustice to postal employees," Riggs said.

Flener suggests a different meaning for the phrase: "Going postal means delivering mail to 144 million mail boxes, 212 billion pieces of mail a year, 260,000 delivery vehicles on the road every day, 704,000 postal employees nationwide. That's going postal."

Over the past 20 years, the Postal Service has implemented a work environment committee in which management and labor attempt to work out problems, improve safety and eliminate tension, Flener said. Letter carriers may file written challenges when they have problems with management.

"Smile and file. That's what I tell them," Riggs said.

The Postal Service has beefed up pre-employment screenings and trained supervisors to look for changes in behavior, including the way workers dress, and changes in personality and mood.

"We've really improved communication on a whole lot of levels," Flener said.

But former Edmond postal workers said the new guidelines would have done little to calm Sherrill's rage.

"He was very withdrawn," said Gene Bray, who was shot in the back but continued working for the postal service until he retired in 1995. "Never spoke a word to him nor did he ever speak to me."

"The demons that drove Patrick Sherrill to do what he did will never be known," Flener said.

Although wounded, Bigler returned to work the next day. He left the postal service later that year and now runs a prison ministry with his wife.

"We realized how precious life was, how precious our friends who were mowed down that day," he said.

Postal workers have no plans to observe the 20th anniversary, said Edmond postmaster Larry Chandler.

"Employees have chosen to deal with those memories in their own way," Flener said. "It's quiet reflection. No great fanfare."