Sometimes it's for the thrill, sometimes it's so they can be a hero.
There are several cases of firefighters who start fires, a phenomenon officially called "firefighter arson."
Kevin Wedick, an Edmonton private fire investigator with the consulting firm Origin and Cause, says that of the cases he's seen in Alberta, most involve volunteer firefighters from small, rural departments.
"Some of these fellows want the excitement," Wedick says. "They want to roll out there with the sirens and go on a call."
In addition to an adrenaline rush, they may also be motivated by financial gain, he says, since fighting a fire as a volunteer also means getting a paycheque.
A 2003 report by the United States Fire Administration calls firefighter arson a rare but serious problem.
"Their main reason for lighting the fire is so they can appear as a hero, either by being the first to spot the flames, or by rescuing people and saving property," says the report.
Other reasons cited in the report were to earn extra money and practise their skills.
As an example, the report mentions a firefighter in North Carolina who would set fire to an occupied house, then return to the scene and rescue the family inside.
Last weekend, a volunteer firefighter in Mayerthorpe, Alta., was charged with 18 counts of arson following a recent rash of fires in the area northwest of Edmonton.
RCMP have said one of the fires included a blaze that engulfed a wooden train trestle and forced the evacuation of a high school and mobile home park.
Michael Schalm, 19, who joined the community's fire department as a junior member when he was 15, is to appear in court on Wednesday. The allegations have not been proven and he has not yet entered a plea.
In 2008, firefighter Mike Hagel of Oliver, B.C., who was sentenced to two years for setting fires in the area. He confessed in a letter sent to media, saying he was suffering from post-traumatic stress disorder and had a drinking problem.
There are two other reported cases in Quebec where firefighters were handed prison sentences for their arsons.
One of the most infamous firefighter arson cases is John Orr, an arson investigator in California who started hundreds of fires in the 80s and 90s, including one that killed four people.
Orr, who was nicknamed the Pillow Pyro because he reportedly started some fires with pillows, was arrested after writing a best-selling novel about a firefighter turned serial arsonist. HBO later turned his story into a movie starring Ray Liotta.