Forty-one minutes before Bosnia's cease-fire began, Namik Brkanic, 19, went to the bathroom, switched on the light and touched off a gas explosion that blew up the four-room apartment he shared with his parents and 11-year-old brother.

Having survived 42 months of Bosnia's bloody war, the Brkanics became the first victims of an uneasy peace that began at 12:01 a.m. today. The nationwide cease-fire is the 35th and, in the eyes of diplomats, most serious since the conflagration erupted in April 1992.

With 70 percent of his body burned, Namik was flown to Italy today in an emergency medical evacuation to save his life. His father and brother were hospitalized here with second-degree burns. His mother is in shock.

The explosion that ripped through their four-room apartment tossed radiators, couches, tables and chairs out a window and plowed their front door into a neighboring flat. It would never have happened at the height of the Bosnian Serb siege, when nothing -- neither water, power nor gas -- was allowed into Sarajevo. Then Serb shelling and sniper fire were the main causes of death; government figures put the city's toll at 10,000 people. But with Sarajevo's utilities partially restored and the guns of Bosnia partially silenced, the prospects for these disasters have increased.

Sarajevo's central Kosevo Hospital has set up a special burn unit to cope with an expected rise in the number of victims of gas explosions. As of today, the facility was packed -- an ominous sign considering that gas has been flowing into Sarajevo for only two days after being stopped since May.

The reason these problems occur is twofold. U.N. experts estimate that over the course of the war, 50,000 households have patched together impromptu gas connections in an effort to keep warm and cook. Before the war much of Sarajevo used coal, but shipments haven't come here since fighting began. Secondly, the natural gas supplied to Sarajevo by Russia is not odorized, so nobody notices when it leaks.

In the Brkanic apartment, for example, the gas had been leaking for seven hours and all the windows were closed when Namik flipped a light switch and the place blew up.

A next-door neighbor, Adil Katica, staggered onto the balcony of his apartment and looked outside. A huge plume of black smoke swirled from the Brkanic family's home. Below him, two cars had been crushed by tumbling radiators and a complete wall of the apartment that collapsed, like a house of cards, onto the street.

Upstairs the Brkanic apartment resembled a mini-earthquake site, with giant blobs of rubble dotting what had once been a tranquil domestic scene. In Namik's room, a model of a Yugoslav air force jet sat unscathed on a mantel. Next to it, where there was once a window, a giant hole gaped onto the street.

"He wanted to be a pilot," said Namik's 17-year-old cousin, Mirha Mandic, who was helping as best she could to clean up the mess today. "Who knows what will happen to him now?" CAPTION: Sarajevo residents relax in a downtown park on the first day after a nationwide cease-fire went into effect.