You need to be maintaining a tax basis schedule of your investment in the LLC. If you know your tax basis, you know whether or not you are at-risk.
The basis schedule needs to be updated annually for the applicable lines on the K-1. As long as your tax basis is positive, you will be at-risk.
*A reminder that posts in a forum such as this do not constitute tax advice.
Also keep in mind the date of replies, as tax law changes.