Conservative Management in Traumatic Pneumothoraces in the Emergency Department (CoMiTED) is a randomised controlled trial to find out whether a collapsed lung (pneumothorax) due to injury (trauma) can be safely and effectively treated without immediately inserting a tube into the chest (chest drain). Both treatments for a collapsed lung (treatment with or without a chest drain) have advantages and disadvantages, but we do not know if one is better than the other. This study will help us find out which treatment is better and whether doctors should change their practice and potentially treat fewer patients with a chest drain.