An employee was at a residential home to perform a gas houseline inspection after repairs. While using a flashlight to see, the employee walked into the laundry room and fell into a 2' x 2' access opening for a crawl space in the floor. A black rug was partially covering the opening. The employee fell approximately 40 inches into the crawl space. The employee sustained three fractured ribs on the left side, fluid on the left side of the lungs, and a bruised right knee.