Stuff reports, via Fark:

[A] man suffered minor burns in a brief but "dramatic" operating theatre fire which is believed to have been caused by flatulence, The New Zealand Herald reported today. The man was at the Southern Cross Hospital in Invercargill to have haemorrhoids removed and was singed in the "exceedingly rare" incident involving his own gas.

Scribal Terror has covered the issue of unintentional surgical patient ignition in relation to polypectomies, but never hemorrhoidectomies. In any event, here's a reprise:

According to an MDSR ( Medical Device Safety Reports ) article called "The Patient Is on Fire! A Surgical Fires Primer,

Virtually all operating room fires ignite on or in the patient, and about 10 surgical patient fires a year come to ECRI's attention through various medical and legal communications. These fires typically result in little damage to equipment, cause considerable injury to patients, and are a complete surprise to the staff.

One little-known source of surgical fires is methane, which can ignite during intestinal surgery, or even during colonoscopies (when a polyp is removed and the site is cauterized). Here's an example from the same article in a section titled "Bowel Explosion":

A methane-producing diet and improper cleansing of the bowel before surgery led to a bowel explosion. Without first venting the bowel, the surgeon exposed the colon and proceeded to enter it using an ESU. The hot ESU tip caused the explosive ignition of the bowel gases, which caused a 10 cm tear of the colon. The patient was otherwise uninjured and subsequently recovered.

Not all outcomes were quite as salubrious however. In the journal Gastroenterology (1979) Bigard, Gaucher, and Lassalle report on a "fatal colonic explosion during colonoscopic polypectomy":

A patient is described who sustained the first reported colonic explosion during colonoscopic polypectomy. Mannitol solution was used for bowel preparation, and the colon was completely clean. During snare removal of a cecal polyp using high-frequency current a loud explosion occurred. In spite of emergency surgery with transfusion of 45 units of blood, uncontrollable hemorrhage persisted from multiple bleeding points, and the patient died. This occurrence seems to us to justify the routine use of carbon dioxide insufflation during polypectomy and the avoidance of mannitol for bowel preparation.

But if you prefer not to think about colonic explosions, you can always think about eyelid flashfires instead.