A pneumatic safety valve prevents dangerously rapid outflow of pressurized air in the event that an air hose ruptures or a pneumatic tool is accidentally decoupled from the hose downstream of the valve. The valve has an internal air conduit in fluid communication with the inlet and outlet ports. The air conduit cooperates with a pivotal flap that selectively closes to prevent a sudden discharge of air in the event of a hose rupture or an accidental decoupling of the pneumatic tool from the hose. By containing the highly pressurized air and preventing the air from rapid discharge, the valve prevents the air hose from flailing or whipping violently, thus eliminating the physical dangers to operators and other personnel in the vicinity of the rupture. This simple and inexpensive valve ensures safe containment of hose ruptures or of accidental disconnections of the pneumatic tool from the high-pressure hose.