AN SMA CHARTER PLT WATCHED A TORN ALTERNATOR BELT FLY PAST THE WINDSCREEN WHILE IN CRUISE FLT. THIS EVENT AND THE SUBSEQUENT ELECTRICAL FAILURE LED TO AN IMMEDIATE DIVERSION TO AN ARPT UNDERLYING SEA CLASS B AIRSPACE WITHOUT COM WITH ATC. ACFT EQUIP PROB CRITICAL FLT DIVERTED.

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I WAS PIC OF A SINGLE ENG VFR CHARTER FLT FROM TACOMA NARROWS ARPT TO YAKIMA ARPT. WHILE LEVELING OFF AT 7500 FT APPROX 35 MI SE OF THE SEATTLE VOR (101 DEG RADIAL); THE ALTERNATOR BELT BEGAN WRAPPING ITSELF AROUND THE SPINNER. WITHIN 30 SECONDS; THE BELT WAS RIPPED IN HALF AND FLEW PAST THE WINDSCREEN. I WENT THROUGH THE EMER PROC FOR ALTERNATOR FAILURE AND BEGAN TO DIVERT TO THE AUBURN ARPT. WITHIN 2-3 MINS AFTER THE BELT FAILED; I WAS UNABLE TO COMMUNICATE WITH ATC AND WAS; IN EFFECT; FLYING THROUGH CLASS B AIRSPACE WITHOUT A CLRNC. UPON LNDG AT THE AUBURN ARPT; I TELEPHONED SEATTLE APCH TO EXPLAIN WHAT HAD HAPPENED. THEY SAID ALL WAS OK AND NO FURTHER INFO WAS NEEDED. ALTHOUGH I DID EVERYTHING CORRECTLY AS FAR AS REGS ARE CONCERNED; I FEEL THAT A MORE THOROUGH INSPECTION OF THE ALTERNATOR BELT PRIOR TO FLT COULD HAVE PREVENTED 'EMER' ACTIONS. A COMPLETE PREFLT INSPECTION WAS COMPLETED PRIOR TO THE FLT; HOWEVER; I FEEL THAT A VISUAL INSPECTION OF THE BELT FOR WEAR AND TEAR WOULD HAVE ALLOWED ME TO DETECT DAMAGE MORE SO THAN A QUICK 'TUG' ON IT TO CHK FOR TENSION.