Cambridge Fire Department and Harvard Police officials rushed to the scene of an explosion in the Jefferson building of the Physics Laboratories this weekend, but said they have not been able to determine the cause of the blast.

The blow-up occurred at 11 p.m. Saturday in the basement of the building on Oxford Street, said Frank E. Murphy, deputy chief of the fire department. No injuries were reported.

The only eyewitness to the event, Walter W. Hagley, a student at the Graduate School of Arts and Sciences, said he was working in the machines shop of the basement at the time.

Hagley said he was using a gas torch to build equipment for an experiment, when suddenly he "heard a loud noise" and was pummelled by shock waves and flying dust.

Hagley emerged unhurt form the incident.

Fire department official have not been able topinpoint the cause of the explosion, but said theythought Hagley's gas torch might have played arole.

Hagley himself said he did not know what causedthe explosion, but he did not attribute it to thework he was doing.

According to the fire department's report,"fresh cracks were evident in the cinderblockwalls" after the explosion.

In an interview yesterday, Hagley seemedunfazed by the explosion.

"I'm still alive," he said.

Hagley said he plans to continue doing hisresearch at Jefferson despite Saturday night'sincident