A total of 136 Montgomery County employees, mostly firefighters and corrections officers, earned at least $40,000 each in overtime pay last year, according to new data posted on the county government’s Web site. In 2012, 94 county workers received $40,000 or more each in overtime pay.

In some instances included in the 2013 data, employees’ overtime far exceeded their total base pay. A corrections officer whose regular salary was $68,201, for example, collected $122,336 in overtime — the most of any county employee. Six fire department employees were paid more than $90,000 each in overtime, pushing their annual earnings above $200,000.

Heavy overtime costs are commonplace in fire departments and other public safety agencies throughout the Washington region and the country. Fairfax County, for example, paid $16.7 million in firefighter overtime in fiscal 2012. Overtime costs in Montgomery’s fire service grew more than 26 percent from 2010 to 2013, from $14.5 million to $18.3 million, according to county figures.

The new salary information is listed on openMontgomery, a Web site officials created to help improve transparency in county government.

Unlike most government agencies, fire departments must provide service around-the-clock and require a minimum number of personnel to safely staff vehicles and stations. With vacation, sick leave, training and other contingencies that take firefighters out of the station house, Montgomery officials say, the county needs 4.5 firefighters to staff each of the more than 280 slots that must be filled every weekday. On nights and weekends, volunteers fill in the gaps.

Montgomery officials defend the overtime outlay, saying it is a lower-cost alternative to hiring new full-time employees, with expensive benefits, to fill empty positions day to day. They estimate that it would take 140 new hires for the 1,300-member service to have personnel ready to fill all positions without overtime.

“I don’t think overtime is a bad thing,” said Tim Firestine, chief administrative officer for County Executive Isiah Leggett (D). “It’s a cheaper way to provide the service when you have a 24-7 operation. The point is, it’s more complicated than looking at what individual people make.”

Overtime can be driven up by a variety of factors. Renovations at the county’s correctional facilities, for example, have required officers to devote more time to escorting construction workers to and from high-security areas where work is underway, corrections officials said. Aspects of the county’s collective-bargaining agreement with the firefighters union creates significant opportunities for firefighters to earn overtime pay.

Most firefighters work a 24-hours-on, 48-hours-off schedule that averages out to a two-week pay period of 96 hours.

Federal labor law allows localities to require up to 53 hours of “straight time” in a two-week period before firefighters are eligible for overtime.

But the county’s contract with the International Association of Fire Fighters Local 1664 triggers overtime at 48 hours. It also provides that hours paid — not merely hours worked — count toward the 48-hour threshold. Sick days, vacation or other earned leave count toward the 48-hour threshold.

A County Council staff report found that between January 2011 and June 2012, more than 300 firefighters received overtime during pay periods in which they worked just half of their regular hours. More than 150 worked entire two-week pay periods with all overtime and no regular shifts.

Leggett, who is running for reelection this year, said Monday that he would like to begin discussing firefighter schedules in the next round of contract negotiations. He said the long hours that some firefighters work create potential safety and productivity issues that need to be explored.

“The question is whether a person working a huge amount of hours is still productive,” he said.

Former county executive Doug Duncan, who is running against Leggett in the June 24 Democratic primary race, agreed that with heavy overtime, emergency workers may start to lose their effectiveness, possibly endangering themselves or those around them.

“At some point, you’re going to hit a breaking point where you’re not filling the positions needed to keep pace with response time, and you’re going to exhaust your work force from all the OT,” Duncan said.

Neither Leggett nor Duncan expressed concern about the impact of overtime on county spending.

But council member Phil Andrews (D-Gaithersburg-Rockville), who is also running for county executive, said he thinks there is a “a sweet spot” that the county has yet to find that strikes the right balance between reliance on overtime and regular staffing.

“There’s been some progress over the years but not enough,” said Andrews, who chairs the council’s Public Safety Committee.