Even as the number of inmates held in city jails has steadily dropped since 2009, overtime at the San Francisco Sheriff’s Department spiked 34 percent last year — another jump for a department that has been scrutinized for working its staff long hours.

Reducing overtime pay hasn’t proved easy for the Sheriff’s Department, which has struggled with staffing shortages attributed to budget woes, workplace injuries and attrition.

“On its face, it’s incredibly concerning, but we need to take a hard look at the facts and circumstances of that increase,” said Supervisor Mark Farrell, who heads the city’s Budget and Finance Committee and has sponsored past legislation to help limit overtime. “The issue definitely hasn’t gone away (citywide), and we have to continue to question every dollar and make sure we are spending it wisely.”

San Francisco spent about $193 million on overtime last year, a 7.5 percent increase from 2014, according to a Chronicle analysis of Recorder’s Office data. The usual suspects tallied the highest overtime bills last year: The San Francisco Municipal Transit Agency spent about $56.2 million, the Fire Department $42.1 million, and the Police Department $36 million.

Compared with those agencies, the Sheriff’s Department — which has deputies both on the streets and in County Jail — recorded a relatively small overtime payout. But it saw a much bigger increase, jumping from about $12.2 million in 2014 to $16.4 million last year.

Staff shortages cited

And while the proportion of the total payroll dedicated to overtime remained relatively steady across city agencies — holding flat near 6 percent in 2014 and 2015 — it grew from 11 to 14 percent at the Sheriff’s Department.

The increase is occurring as the city’s inmate population shrinks. The average number of people held in San Francisco jails dropped 20 percent between fiscal years 2011-12 and 2014-15, according to a January report by the city Controller’s Office. While declines in the jail population have led to dips in overtime spending in the past, the number of overtime hours at the agency actually increased 60 percent over the time period.

The Sheriff’s Department blames the growing overtime costs largely on staffing shortages. The number of full-time employees fell by about 7 percent between fiscal years 2010-11 and 2014-15, due in part to a higher than expected rate of attrition.

Injuries within County Jail also increased substantially between 2012 and 2014, leading to a high number of deputies on long-term sick leave. There are currently 40 people on disability, 20 of whom aren’t expected to return to work, according to Sheriff Vicki Hennessy. Since people on disability can’t be permanently replaced by new hires, each month someone is out forces the agency to use as much as 269 hours of overtime, according to a June audit by the budget and legislative analyst.

Workplace accidents

An inadequate injury prevention program probably contributed to the high number of workplace accidents, the audit found. Paying so much disability eats up money the department could use to hire new staff.

“This might be a catch-22,” said John Violanti, a professor at the University at Buffalo’s School of Public Health, who has studied the effects of fatigue on police. “Because officers are working overtime, they’re getting injured more, because they’re getting injured more, they’re on sick leave more, and because they’re on sick leave more, other officers need to work more overtime.”

Hennessy, who replaced Ross Mirkarimi as sheriff last month, said her department is closely monitoring compensation and plans on fully addressing the issues brought up by the audit — including its heavy use of overtime — after the agency receives its 2016-17 budget.

“Sometimes overtime is cheaper, but ... there’s a tipping point,” she said. “We haven’t quite figured out what the tipping point is, but we want to make sure we’re doing all that we can to respond to the needs of the department and the services that we provide.”

One of her biggest priorities is hiring and training deputies. To reach 100 percent staffing levels, the agency needs to bring on nearly 140 full-time employees over the next two fiscal years, according to the Budget and Legislative Analyst’s Office. Some of those positions require mandatory staffing under city law, leaving the department few options, Hennessy said, aside from overtime.

It may be a while, though, before the department has a full force. If the city’s new budget, out in June, allocates enough to hasten hiring, it could take at least nine months to vet and train a new class of sheriffs.

Highest tallies

While there’s an overtime cap for employees — 522 hours per fiscal year — the administrative code allows waivers. Once deputies receive clearance from the city’s Human Resources Department, overtime tends to concentrate among a handful of volunteer workers. Some pick up a surprising number of shifts.

Of the 10 city employees who tallied the highest overtime bills last year, half worked for the Sheriff’s Department.

Deputy Santiago Antonio, who works in County Jail, earned nearly triple his base salary of $121,500 thanks to $209,000 in overtime, the highest such payout in all of 2015. Another corrections deputy, Barry Bloom, took in about $170,000 in overtime, the second highest in the city.

Both employees have a history of working far more than 40 hours per week. Bloom logged 1,026 hours of overtime in 1999, according to a past civil grand jury report, and he put in 1,730 hours of overtime in 2006. Antonio worked an extra 2,226 hours in 2006 — or a total of 83 hours per week on average.

Neither deputy could be reached by The Chronicle, and the sheriffs union did not return repeated requests for comment.

‘Difficult to justify’

“Absent an emergency situation or some unusual event, significant overtime costs are difficult to justify,” said Jon Coupal, president of the Howard Jarvis Taxpayers Association. “When people work long hours in high-stress jobs, the issue of effectiveness comes into play. Do you want a police officer who has been on his feet for 36 hours straight?”

The city says it is working with the department to resolve the rising overtime costs.

“The Sheriff’s Department staffing levels have gone down over the past couple of years due to higher than expected retirements ... (and) increased use of overtime to manage unexpected retirements is an appropriate, short-term approach,” Kate Howard, the mayor’s budget director, said in an e-mail. “We are actively working with the department to back-fill all retirements and maintain an appropriate balance between straight time and overtime use.”

Joaquin Palomino is a San Francisco Chronicle staff writer. E-mail: jpalomino@sfchronicle.com Twitter: @JoaquinPalomino