A construction worker was killed and another was injured in a tunnel collapse near Lake Mead, Nevada, on Monday, according to an announcement by the National Park Service.

The tunnel was under construction when a tunnel ring came loose and made contact with grout material that was highly pressurized, causing the collapse, which trapped 18 workers and exposed at least 25 others to toxic gases.

The tunnel is one of many currently under construction by the Nevada Water Authority as part of a larger project called Intake No. 3, which is scheduled to be completed by 2014.