Carpal tunnel syndrome and tendonitis are two common upper extremity cumulative trauma disorders (CTD) related to repetitive and forceful activities in industrial environments. Reducing the muscular force during activities such as the operation of a pistol grip hand tool could result in lower incidence of CTDs. The objective of this research was to reduce the muscular contribution to the grip force using an active orthosis system. A novel soft, pneumatic grasp assist device, that used a unique design of sinusoidal bellows oriented at 45 degrees, was designed to augment the users' strength during operation of pistol grip hand tool. The optimized design was fabricated using rapid prototyping. Device effectiveness was quantified by measuring muscle activity and grip force during an in vivo study of a common industrial activity. Nine subjects experienced with power tools employed by an automobile manufacturer installed 18 fasteners using a pistol grip DC tool with and without the grasp assist device. Surface electromyography (sEMG) was used to measure the activity of four muscles commonly associated with grasping. Results showed that the grasp assist significantly reduced the mean, combined, normalized muscle activity by 18% (p<0.05). Muscle activation results were contextualized using the revised strain index (RSI). The grasp assist device trial yielded a significantly lower mean RSI value than the typical trial by 13% (p<0.05). The study showed that using an active grasp assist orthosis could reduce the incidence of CTDs in able bodied industrial workers using DC hand tools.