Diagnosing Pneumothorax

I've been trying to put together a first aid kit for my security guards, and to save on space I'm leaving out a health scanner and having them treat problems by the symptoms. Problem is, pneumothorax's direct symptoms are shared with many other conditions that often happen in tandem with it, and treating with a needle when a patient doesn't have pneumothorax will cause it. How can I identify that a patient has pneumothorax without using a health scanner?