A helmet blastometer for characterizing the direction, speed, magnitude, and duration of a blast event to determine the likelihood of blast-induced traumatic brain injury (biTBI). A set of external sensors, each having one or more time of arrival (TOA) gages, is mounted at various positions on a rigid outer shell of the helmet. Each external sensor includes a first TOA gage that produces a TOA signal in response to a fast rising blast induced positive pressure change above a predetermined threshold. These positive pressure change TOA signals are received by a receiver and analyzed to determine direction, speed, and magnitude of a blast. At least one of the external sensors may also include a second TOA gauge that produces a TOA signal in response to a negative pressure change below a predetermined threshold. The positive and negative pressure change TOA signals from the same external sensor are used by the receiver processor to determine blast duration. In another embodiment, a second set of internal contact pressure sensors is connected to an inner liner of the helmet to detect contact pressure on a user's head. Preferably, the receiver processor determines that a biTBI has likely been sustained by when one or more of the blast direction, speed, magnitude and contact pressure has satisfied a predetermined biTBI threshold, upon which a biTBI warning indicator may be triggered.