The excesses, though they are neither illegal nor proscribed by departmental policy, represent yet another challenge for Fire Commissioner Roderick Fraser, the department’s leader since 2006. Fraser has repeatedly battled the powerful union and the department’s entrenched culture to curb practices that have diminished the department’s effectiveness and saddled it with needless costs.

In an interview, Burton acknowledged he accumulated an “excessive amount of time owed,’’ but noted there was no prohibition on doing so and said he was never disciplined. O’Callaghan, who has been on unpaid sick leave, declined to comment for the story.

The extent of both practices is undoubtedly far higher than these numbers reflect, because the department does not have a systemwide computerized record for borrowed workdays before 2006. For prior years, the only way to gauge the numbers is to comb through day-to-day paper records for each firefighter — which the Globe did for three firefighters, including Burton and O’Callaghan.

One firefighter who was given credit for working 269 shifts for others actually called in sick for 107 of those shifts.

A second form of shift-swapping abuse has a more tangible — and extremely costly — bottom line. Between January 2006 and last September, firefighters who had agreed to work shifts for others called in sick 29,000 times, forcing the department to pay millions in overtime to others to fill the shifts.

The actual cost of this practice is difficult to assess — the colleagues who worked unreciprocated shifts are not paid extra for that time — but it means that many firefighters have received pay, benefits, and retirement credits for work performed by others.

Nearly 70 other firefighters owe comrades between three months and a year of workdays.

Timothy P. O’Callaghan, another firefighter with outside business interests, has filed for his pension based on years of service. That means he would receive credit for 391 shifts — about two years work — that others worked in his stead, and which he did not repay, according to Fire Department personnel records.

One firefighter, Gregory L. Burton, owes his firehouse comrades 554 shifts — nearly three years of work — for shifts he borrowed over five years while he was tending to a successful real estate business, according to department records. In 2004, for instance, Burton had other firefighters work 124 shifts for him, while Burton himself worked just 34 scheduled tours.

But there are scores of Boston firefighters whose shifts have been covered by others for weeks or months at a time, with no record they have ever reciprocated and worked off the debt.

It is a familial courtesy as intrinsic to the culture of Boston firehouses as shared chicken dinners. When a firefighter can’t make his shift, a colleague steps in, on condition the favor will be returned.

The Globe could find no evidence that any of the firefighters who have amassed substantial IOUs have paid others to work for them. Fraser and Keating said they also possess no such evidence, although both acknowledged the practice occurs.

The lack of accounting — and the absence of limits that other fire departments routinely impose on shift swaps — has nurtured a subterranean culture in which some firefighters pay cash to others to work their shifts, or repay the obligation by doing outside work like home renovation projects for their firehouse creditors, according to interviews with several firefighters, who asked that they not be identified by name.

What’s more, Fraser may have undercut his standing to demand tighter controls on swaps: Last March, he bowed to entreaties from Burton and others and rehired the firefighter. And Fraser said recently that the 2007 resignation erased Burton’s obligation to repay the 554 days he owed.

Yet compliance was rare: Fourteen of the 20 have borrowed even more shifts since being warned, according to a Globe review of the records. None have been disciplined. Department officials said they were unaware of the lack of compliance until the Globe called it to their attention.

In fact, just seven firefighters were summoned to headquarters, according to records that Captain Stephen Creamer, the personnel supervisor, reviewed at the Globe’s request last week. One of those seven, Burton, resigned rather than report for the dressing down. In the cases of 13 others, their commanders were told to warn them, Creamer said.

The department, however, has done little to curb the shift-swap abuses — and less than Fraser and Keating, in a December interview, claimed they had accomplished. In 2007, they said, 30 of the worst offenders were summoned to headquarters and warned they would face possible suspensions if they continued to borrow more shifts than they repaid. All but one complied, they said.

During a December interview, Fraser and Fire Chief Ronald Keating said they are working to change the culture of the department. “It’s not going to be done overnight,’’ Keating said. “It’s going to be done in small baby steps and we’re taking those steps as we talk.’’

As has been the case with the other abusive practices, the runaway shift deficits accumulated by dozens of firefighters underscore a workplace ethos in which the personal needs of many firefighters appear to trump those of the fire service.

In 2008, for example, the Globe reported that scores of firefighters were staying out on injured leave for extended periods, and that more than 100 firefighters were awarded higher disability pensions after claiming career-ending injuries occurred while they were filling in for superiors at higher pay rates. That practice led to federal indictments and changes to state pension laws.

There is another feature to the system, a perk the department is reluctant to halt: Some firefighters work a substantial number of added shifts in the winter so they can take much of the summer off. And vice versa: Other firefighters are happy to work extra summer tours so they, in turn, can escape to Florida for part of the winter.

Those swaps, which represent the bulk of the shift-trading, most often even out, with firefighters making clean exchanges. There is no payroll adjustment for swapped shifts, just an understanding each firefighter will ultimately work the shifts he or she has been paid for. A small percentage of the deficit on the books represents acts of compassion. One example: shifts worked for colleagues tending to ill family members, with no expectation they be repaid.

Contractually, firefighters are supposed to work 16 shifts a month — half of them 10-hour daytime shifts and the other half 14-hour nighttime shifts. In many firehouses, however, they swap shifts so they work 10-hour and 14-hour shifts back-to-back, from 8 a.m. to 8 a.m. That system, a boon to those with second jobs, allows firefighters to work eight 24-hour shifts a month.

Shift-swapping began four decades ago as a benign way for firefighters to consolidate their schedules, in a way that is done in numerous other departments across the country.

Most big-city departments have such limits; in Denver, for instance, firefighters are generally not allowed to accrue a deficit of more than three shifts.

Rich Paris, president of the Boston firefighters union, the International Association of Fire Fighters Local 718, said in an interview that “there are some guys taking advantage’’ of the system. But on the issue of whether the city should be able to impose limits, Paris said: “Why should the majority of our guys get hurt over something [when] a certain percentage of guys are doing something wrong?’’ The issue, he said, can only be settled through collective bargaining.

Fraser said he will, however, explore whether the city can recoup money from retired or retiring firefighters, like O’Callaghan, who received full pay and retirement credits for work that others actually performed.

This has proved to be a high bar: Last year, for example, the city increased the size of a pay raise for firefighters in return for the right to conduct random drug testing.

Keating said the department is developing a system that will more effectively monitor swaps, but limiting the number of shifts any one firefighter can rack up could be difficult. In 1996, when shift-swapping became part of a contract dispute, an arbitrator ruled that the department could not impose a limit without negotiating it through collective bargaining.

One telltale sign that much of the debt has been settled privately: Fraser and Keating said not a single firefighter who is owed shifts has ever filed a complaint. Under-the-table cash payments would violate tax laws if the income is unreported.

The firefighter who owes the most shifts since 2006 is Kenneth T. Gibson, at 202, according to the records. But unlike Burton and O’Callaghan, Gibson’s shift deficit in the prior four years was minimal, just 27. Overall, Gibson owes the equivalent of a year’s worth of shifts that he said he borrowed from four or five colleagues. He declined to identify any of them and the department does not keep track of who owes whom.

O’Callaghan, who was developing properties in Dorchester, relied on others to work his day shifts for him. In 2005, for example, O’Callaghan worked just two day shifts, while his peers worked his shifts 96 times. In return, he worked just nine overnight shifts.

“Yes, I owed an excessive amount of time,’’ Burton said. And when he was summoned to headquarters in 2007, he said, “I elected to resign. I left because of my other obligations, and I could not make the commitment the department wanted.’’ Burton said he never paid anyone else to work for him.

In 2004, for example, Burton worked just 13 day shifts because of his business commitment; and 21 overnight shifts. Other firefighters filled in for him on 124 shifts. Not once that year did Burton reciprocate. The following year, he borrowed 145 shifts, and worked just four in return.

Burton, who is still president of his own Boston real estate company, said in an interview that business was so good that over time, he had six other firefighters working for him as brokers.

In a database the department provided to the Globe last fall that covers 2006 to September 2010, Burton is listed as owing 148 workdays. But that obligation does not count 410 shifts he borrowed and left unpaid from 2002 through 2005. In 2006, Burton earned about $375 a shift.

Fraser said it was not until 2007 that senior department officials became aware of the extent of the problem. “It was reported by one of our field deputies that they had a problem with some of their people basically accumulating so many swaps that they never saw them,’’ Fraser said during a lengthy interview in December.

Under department regulations, district chiefs are required to approve every swap in advance. But the department abandoned that practice several years ago, according to Keating.

Tyler said the swap system is an “administrative nightmare’’ for the department. District chiefs, he said, cannot be assured that firefighters who appear for duty are accustomed to working together, in an environment “where teamwork is very important.

“The taxpayers cannot support that kind of practice,’’ said Samuel R. Tyler, president of the Boston Municipal Research Bureau, a business-supported watchdog group.

Gibson is in the hole to others for time spent pursuing two outside interests. According to Federal Aviation Administration records, Gibson is rated as a commercial pilot and multi-engine flight instructor. Corporate records list him as president of a Rhode Island-based aviation company.

And last May, Gibson received a master’s degree in business administration from Northeastern University.

“This was the only way I was able to go to graduate school,’’ Gibson said in explaining how it is that others have worked so many shifts for him. “I used this practice to go to school.’’ The system, he asserted, “was wide open. . . . There has never been any limit to the amount of time you could owe.’’

Gibson asserted that he has already begun to pay down his shifts. He said he expected it would be easy to do over the course of several years.

Cost of calling in sick The department’s inability to monitor personnel practices has been costly: For example, the department was unaware how many firefighters were calling in sick for the shifts they promised to cover until the Globe pointed out the numbers. The department’s inability to monitor personnel practices has been costly: For example, the department was unaware how many firefighters were calling in sick for the shifts they promised to cover until the Globe pointed out the numbers.

In the 56 months starting in January 2006, firefighters on tap to work for colleagues took sick days 29,401 times.

According to the records, 79 firefighters called in sick 50 times or more after they agreed to take someone else’s shift. Atop that list was Bradley Andrews, who took sick days for 107 of the 269 shifts he was scheduled to fill in.

Andrews, who was assigned to Ladder 11 in Brighton, retired last January. “If I called in sick, I wasn’t feeling well,’’ Andrews said in a telephone interview. “I worked 34 years for the Boston Fire Department. I think it was honorable service.’’

About half the time when someone is sick, the department has to bring someone in on overtime, at one-and-a-half times regular pay. That would put the cost to taxpayers for the shift-swapping sick calls at between $6 million and $8 million since 2006, according to a Globe calculation based on the department’s average overtime rates.

Policies around the US Shift-swapping is common in fire departments, but so are stringent controls on the practice, according to a Globe survey of big-city fire departments across the country. And the Boston Police Department, which permits its officers to swap shifts, turned over to the Globe records showing deficits to be virtually nonexistent. Shift-swapping is common in fire departments, but so are stringent controls on the practice, according to a Globe survey of big-city fire departments across the country. And the Boston Police Department, which permits its officers to swap shifts, turned over to the Globe records showing deficits to be virtually nonexistent.

In San Francisco, the Fire Department instituted strict limits to stem excesses. “We had instances of people working way too much and others taking too much time off,’’ said Mindy Talmadge, department spokeswoman. “It’s better for the health of our firefighters to limit how much time they can work. We’re protecting the public, so we want our people to be as sharp as possible.’’

Boston’s system perplexed fire officials in other cities. “That sounds like a tremendous amount of time, 100 shifts,’’ Denver public information officer Lieutenant Phil Champagne said. “The problem with that is, how do you pay people back?’’

Also perplexing, to some, was Fraser’s decision to bring Burton back onto the department payroll.

When Burton resigned in 2007, Fraser said, “he was the number one offender. We called him in to talk, to tell him to stop. It was alleged he was running a real estate empire. It was alleged he was paying people to work his shifts.’’ But, Fraser added, there was no proof of such payments.

Last March, with the housing market in dire straits, Burton asked to be rehired and Fraser agreed. The firefighter, Fraser said, “came to understand the error of his ways. . . . He missed working for the department, and it’s a great place to work. He asked to come back. We had many a long discussion with him about what we expect, what our expected behavior was, and I gave him a chance.’’

And what about the days of work Burton owed his colleagues when he left in 2007? According to Fraser, that obligation was officially erased when Burton resigned. By that standard, Burton owes only two shifts he borrowed last year.

Asked whether the firefighters who are owed those 554 shifts have any recourse, Fraser said, “That’s [for] any firefighters he may have owed . . . to discuss with him.’’

In addition to Borchers and Tziperman Lotan, this article was reported by Stefanie Geisler and Cecilia Akuffo for a seminar in investigative reporting at Northeastern University. John M. Guilfoil of the Globe staff contributed reporting. Their work was overseen by Walter V. Robinson, Northeastern journalism professor and former editor of the Globe Spotlight Team. Robinson can be reached at wrobinson@globe.com. Confidential messages can be left at 617-929-3334.

© Copyright 2011 Globe Newspaper Company.