One quick take-away from the Department of Defense article:

Injury report from trials:

"The Airman received second-degree burns (blisters) from an overexposure to the Active Denial System due to procedural errors.

Later whilst spruiking the weapon as 'non-lethal', the article says:

"For this technology to become lethal, the energy beam exposure would have to be sustained and prolonged."

So it is lethal. Just depends how long you train it onto someone. You've already immobilized them - if you want to fry 'em - just keep your finger on the trigger of your ray gun.

The report assures us that wont' happen due to changes made in the 'operating procedures'.