The purpose of this paper is to present a method to determine the timing of individual rib fractures during dynamic side impact tests on human cadavers. The technique utilizes a total of 18 single axis strain gages placed throughout the thorax. Specifically, single axis strain gages were placed on ribs three through eight on the left and right lateral portions of the thorax, as well as the posterior portion of the impacted side. By utilizing this technique, the exact timing of an injury level can be characterized relative to the mechanical parameters. In order to simulate thoracic side impact loading from a severe car crash, a custom pneumatic impactor was designed and fabricated. The thoracic testing was conducted at an impact speed of 12 m/s and an impactor mass of 23.4 kg. The impacting surface was a flat rigid plate, with a length of 41.5 cm and a width of 25.5 cm, instrumented with a load cell and accelerometer. Thoracic rods attached to ribs five, seven, and nine were used along with potentiometers to measure lateral chest compression. All data was sampled at 15 kHz. The time histories of each strain gage were analyzed to determine the time of fracture which could then be compared directly to the chest compression at that exact time of each rib fracture, thereby creating a non-censored data set. Lateral fractures on the impacted side occurred between 2% and 9% of compression measured at rib 5. Posterior fractures on the impacted side occurred between 8% and 16% compression measured at rib 5. Lateral fractures on the non-impacted side occurred between 28 % and 32% compression measured at rib 5. Finally, the primary loading mode of the ribs varied with respect to thoracic region. The exterior portion of the ribs on the lateral region of both the impacted and non-impacted side was placed in compression, while the posterior region of the impacted side was placed in tension. The peak strain at failure ranged from -4192 mstr to -20194 mstr for lateral portions of the thorax and from 7491 mstr to 14142 mstr for posterior portions of the thorax. Using rib fractures as the parameter for AIS scores, it was found that AIS=1 injuries occurred at a chest compressions of 2% to 3%, AIS=2 at 4% to 7%, AIS=3 at 7% to 9% measured at rib five. It is expected that this data will augment and clarify the foundation of thoracic injury risk functions for side impact.