"These large metal structures are cyclone dust collectors installed at an industrial cabinetmaking facility. They are connected to a dust collection system that is designed to remove suspended combustible particulates in the factory. When organic materials-in this case wood dust-are mixed with air, there is a chance the mixture will ignite in a deflagration creating an explosive pressure increase in the duct system. To reduce the damages that could be caused by explosion, dust collectors are provided with exhausts or vents that allow the explosion to go out of the system before causing additional further damage. In today's illustration, the square devices mounted on the cyclones are panels that release in the event of a pressure increase."
Coffee Break Training - Fire Protection Series No. FP-2011-14
United States Fire Administration: http://www.usfa.fema.gov/