(HERRIN, IL) — Four construction workers were injured when the scaffolding they were on collapsed at Herrin Hospital early Thursday morning. According to WSIL-TV, the four men fell more than 20 feet when the collapse happened. Three of the men are in critical condition.  Two were airlifted to a St. Louis hospital. One was airlifted to Evansville. The other man was treated and released at Herrin Hospital.  A total of eight construction workers were laying brick at the hospital when the accident happened. Federal investigators are still investigating the cause of the accident.