I understand fat freezing starts at-5. Is it safe to go higher, like -10?

mfountain,
The temperatures used in Coolsculpting have been rigorously evaluated to maximize fat reduction while maintaining a substantial safety margin. Continual temperature monitoring is utilized during the treatment to assure safety. During the treatment the skin reaches about -11 degrees Celsius with the superficial fat getting to about -8 or -9 degrees Celsius and the deeper fat reaching approximately 0 to +4 degrees Celsius. The temperature of the fat is the critical aspect of CoolSculpting to achieve cryolipolysis or fat cell destruction. The special CoolSculpting wipes used on treatment area lowers the freezing point of the skin and allows the skin to withstand the colder temperatures.
Be Well
Dr G - CoolSculpting University East Coast Medical Director

Careful monitoring of the temperatures with constant feedback, ensures that no burns occur. This is unique to CoolSculpt. One of the many reasons to only use Coolsculpting by a officially trained specialist who has been to Coolsculpting University.

CoolSculpting does not actually dip below 0 deg Celsius.  In fact it stays slightly above that.  Negative temperatures would certainly cause damage to fat cells, but it would also cause damage to skin and nerve cells.  The CoolSculpting machine carefully measures skin surface temperatures during the procedure to provide controlled cooling.  This prevents any skin or nerve cell damage.  
Hope this helps,
Dr. Garry K. Kim