[en] Most irradiated quartz samples show a fast decaying CW-OSL (continuous-wave optically stimulated luminescence) signal known as the fast component (FC, σ_470nm∼2.3x10¹⁷cm²) which is well separated from the more slowly decaying components and is commonly used for dosimetry. Some quartz samples additionally show an OSL signal that decays much more rapidly than the FC, termed as the ultrafast component (UFC). In this paper we report on the physical characteristics of the UFC in two different sets of samples from South Korea and Sweden using various measurement techniques. We conclude that the UFC arises from a shallow electron trap distinct from the FC. Since it rapidly depletes (thermally) at the room temperature, the presence of UFC in the OSL signal can lead to significant dose underestimation; it is recommended that UFC be removed by high temperature preheat (>200 deg. C) and/or rejection of the very initial OSL signal