How do you know who is most likely to get tension pneumothorax?

Size of air leak: Pnuemothorax (ptx) occurs when air escapes from the lung causing the lung to collapse. This may occur after an injury to the lung or if a outpouching of the lung (a bleb) ruptures. If too much air leaks out, the pressure in the chest can build up to the point that pressure is put on the heart and large blood vessels in the chest and cause tension ptx. This can be fatal if not treated promptly.

Trauma, other: Prior to a tension pneumothorax there is a usually a traumatic event that leaves a hole in the lung and no mechanism for that air to leave. Other causes of tension pneumothorax (spontaneous, emphysema, endometriosis(in the chest), rare genetic causes) are not so predictable... And even most folks with chest trauma don't get one (stab wounds and bullets tend to leave a hole for the air to leave).