The Federal Motor Carrier Safety Administration has issued an emergency regional declaration for Tennessee in the wake of a tornado that ripped through Nashville recently. It exempts drivers helping with relief efforts from Hours of Service regulations. Only motor carriers and drivers providing direct assistance to the emergency in Tennessee are exempt. The exemption remains in effect either for the duration of the emergency or until April 2nd, whichever comes first.
You can read the declaration at the FMCSA website.