The three highest-paid city of Pittsburgh employees last year were paramedics, each earning more than $130,000, mostly in overtime pay.

Their earnings were a symptom of understaffing that results in mandatory overtime within the Emergency Medical Services Bureau, which handles some 55,000 incidents a year. It's a situation many paramedics like, since it allows them to make more than police and firefighters, who have higher base salaries. But experts say it may not be sustainable and tired workers could make mistakes.

Paramedics "are dealing with life and death issues," said William G. Sirois, senior vice president and CEO of Boston-based Circadian Information, a consulting firm advising round-the-clock industries including ambulance services. Sustained, rampant overtime "is setting up the city for huge liability."

"The main concern is that we're delivering great service to the residents, and as long as the individuals are alert and doing their job in a way that keeps the residents safe, that's what's very important," said Mayor Luke Ravenstahl.

The bureau took a hit in 2003 with the layoff of 21 junior-level emergency medical technicians. As employment dropped from nearly 200 to around 154 now, overtime pay surged from around $2.2 million a year to last year's $2.75 million, according to unaudited figures. Base pay for medics totaled $8.6 million.

Mayoral spokeswoman Alecia Sirk said some of the overtime was the result of vacancies held open during an effort to recruit and train minorities and women, which will result in three new medics. EMS Chief Robert McCaughan said he's hoping to hire eight paramedics by May, boosting the number to 162.

Meanwhile, overtime has been a bonanza for some.

Crew Chief Jerome R. Wasek is perennially among the best-paid city workers, and last year topped the list at $145,849, including $87,240 in overtime. Ranked second and third were veteran paramedic Anthony N. DeSantis and Crew Chief John H. Soderberg, each boosting base pay in the low-$50,000 range with $80,000 in overtime. That means their average work week was around 80 hours.

"All three of those guys, they just work," said Jeff Vesci, president of the Fraternal Association of Professional Paramedics. "People have bought into the idea that in order to be able to make money in the system we're in, you have to do it."

Mr. Sirois said that productivity plunges after someone has worked 55 or 60 hours in a week, while cardiovascular, gastrointestinal and sleep disorders, plus divorce rates, rise with long hours and night shifts. The difference between limited overtime and long-term overwork, he said, "is fatigue and human error and health and the messed-up lives that come from it."

Paramedics who asked not to be identified, because of a city policy against rank-and-file employees talking to media, described a chronically shorthanded bureau that often has them working 16 hours, going home for eight, then logging another 16. They said they can usually handle that lifestyle -- and they need the money.

Unlike firefighters, who work 24-hour shifts, paramedics can't sleep during work hours. In the summer, when vacations and special events drive up hours, some medics call in sick rather than face another 16 hours, mandating overtime for others.

Chief McCaughan said a typical eight-hour shift involves handling four to seven emergencies or transports.

Even in winter, overtime is available for those who want it. During a two-week pay period last month, Crew Chief Paul A. Sabol logged 163.5 hours worked, for a $5,819 paycheck. He earned $124,989 last year.

"That's nice earnings, and they may well deserve all those hours. But one has to ask, 'What are the effects of working all of those hours?'" said James Craft, professor of business administration at the University of Pittsburgh's Katz Graduate School of Business.

He said relentless overtime can lead to absenteeism and "presenteeism" -- when an employee is at work, but not functioning well because of fatigue.

Mr. Vesci noted that medics are limited to working 20 hours in any 24-hour period -- and it usually doesn't reach that threshold. "Sixteen hours is pretty much the limit, and we've been doing it for years," he said.

Mr. Sirois said Circadian studied paramedics in Austin, Texas, who were working 24-hour shifts with some opportunities to sleep. Circadian found they were being pushed "way beyond the brink." His words to any organization that puts overworked employees in ambulances for long days packed with emergencies: "Hope you've got some good attorneys. You're creating or absorbing an inordinate amount of risk."

Overtime could have a big impact on the city's half-empty pension fund, too, thanks to a provision new to the paramedics' union contract granted by the late Mayor Bob O'Connor in 2006.

Retiring paramedics age 55 or older with 20 years of service get pensions based on half of their earnings -- including overtime -- during the last three or four years of service, depending on when they were hired. Previously, their pensions were reduced by the amount of any Social Security they collected, but the new contract eliminated that offset.

City Controller Michael Lamb, a member of the Municipal Pension Fund board, looked over a list of the top-earning paramedics, some of whom are a few years from pension eligibility.

"That's incredible, that it's that high," he said. "When you see those kinds of numbers, given what the pension situation is, that is cause for concern."

He said he may expand an ongoing audit of the EMS Bureau to include overtime practices.

Last year 57 city workers made more than $100,000, including eight paramedics, 14 police officers, 31 firefighters and four nonunion workers. The mayor earns $98,924.

Police overtime has remained steady, with premium pay at around $7.1 million a year. Security details that police work for private firms are now run through the Police Bureau and that private pay is included in their city paychecks, making those earnings publicly available for the first time.

The top-earning Police Bureau employee, Lt. Thomas J. Atkins, took in base pay of $78,445, plus $53,468 primarily from managing and working details at PNC Park and Mellon Arena. The bureau's second-highest-paid employee, Sgt. John H. Fisher, got base pay of $67,296, plus $59,192 in overtime and details, mostly at Heinz Field.

Two years of hiring has pushed firefighter premium pay -- mostly overtime -- down from $12.6 million in 2006 to $9.3 million last year, according to preliminary spending records. The top-earning firefighter last year was Deputy Chief Harry J. Scherer, making $129,460, including $29,832 in premium pay.

Finance Director Scott Kunka has sought the right balance between the costs of overtime for veteran firefighters and the expense of hiring, training and providing benefits for new recruits. "There's going to be a break-even point where it becomes more advantageous to hire people" than to make veterans work more, he said. He has not analyzed EMS overtime.