Some employees may be required to stay on site for extended periods of time as a result of Sandy. Here is summary of the FLSA payment rules for non-exempt employees from the DOL website:
Sleeping Time and Certain Other Activities: An employee who is required to be on duty for less than 24 hours is working even though he/she is permitted to sleep or engage in other personal activities when not busy. An employee required to be on duty for 24 hours or more may agree with the employer to exclude from hours worked bona fide regularly scheduled sleeping periods of not more than 8 hours, provided adequate sleeping facilities are furnished by the employer and the employee can usually enjoy an uninterrupted night's sleep. No reduction is permitted unless at least 5 hours of sleep is taken.
Keep in mind state law may be more restrictive and employers must comply with whichever law is more beneficial to the employees.