The deaths of four people killed on zip lines and other challenge courses this summer has drawn attention to a regulatory safety net full of holes.

After the death of 12-year-old Bonnie Sanders Burney, the North Carolina General Assembly swiftly passed a law requiring the state to research possible regulations.

But the federal government does not regulate the challenge course industry. Nor does it keep data on how many courses exist or how many accidents occur. While some states have codified regulations, others allow operators of zip lines and high ropes courses to self-regulate.

Burney was soaring over a 40-foot ravine at her sleep-away camp in the Blue Ridge Mountains when the tether attaching her to a dual zip line snapped.