Over the last 10 years, several flameless venting devices have been globally available to extinguish flames discharged from a deflagration vent. These devices have primarily been used on industrial equipment located indoors with the potential for explosions or deflagrations. Both NFPA 68 and VDI 3673 guidelines prohibit the discharge of deflagration vents inside of buildings, and prescribe the use of vent ducts to direct the discharge outdoors to a safe location. This, however, requires an increase in vent area to overcome inefficiencies due to the discharge restrictions of the vent duct. The use of devices to extinguish flame from deflagration vents also results in less efficient venting. The efficiency of these devices was evaluated via largescale deflagration testing. Volumes from 0.5 m(3) to 4 m(3) were utilized with vent area ratios (A/V-2/3) in the range of 0. 1 to 0.3. Tests were conducted with fuel dusts having Ksts of tip to 300 bar.m/sec. The effect of vent static burst pressure was also evaluated. Several methods of validating flame extinguishment were utilized and external effects were measured, including pressure and sound measurements outside the flameless venting device, and temperature on the surface of the device.