An assembly comprising: an air cannon, the air cannon having a pressure vessel, a discharge valve, and a discharge tube assembly, the discharge tube assembly comprising a fluid passageway and a blast guard valve, the discharge valve being capable of opening and closing, the discharge valve allowing gas having a positive gauge pressure to be discharged from the pressure vessel into the fluid passageway of the discharge tube assembly when the discharge valve is open, the discharge valve preventing gas from being discharged from the pressure vessel into the fluid passageway of the discharge tube assembly when the discharge valve is closed, the blast guard valve being capable of opening and closing, the blast guard valve obstructing the fluid passageway of the discharge tube assembly when closed and allowing gas to pass through the fluid passageway when open, the discharge valve and the blast guard valve being operatively connected to each other in a manner such that the discharge valve can open only when the blast guard valve is open, the discharge valve and the blast guard valve being operatively connected to each other in a manner such that the discharge valve opens in response to the blast guard valve being open, the discharge tube assembly is configured and adapted such that the opening of the blast guard valve causes a signal in the form of gas having a positive gauge pressure to reach the discharge valve, the pressure vessel supplying gas having the positive gauge pressure that forms the signal, and the discharge valve is configured and adapted to open in response to the signal, characterized in that the air cannon further comprises a trigger valve being operatively connected to the pressure vessel via a first gas passageway and to the discharge valve via a second gas passageway, the trigger valve being capable of opening and closing, the trigger valve operatively connecting the first and second gas passageways when open and operatively disconnecting the first and second gas passageways when closed, the trigger valve being mechanically actuated by the blast guard valve when the blast guard valve is open in a manner causing the trigger valve to open in a manner creating the signal. an air cannon, the air cannon having a pressure vessel, a discharge valve, and a discharge tube assembly, the discharge tube assembly comprising a fluid passageway and a blast guard valve, the discharge valve being capable of opening and closing, the discharge valve allowing gas having a positive gauge pressure to be discharged from the pressure vessel into the fluid passageway of the discharge tube assembly when the discharge valve is open, the discharge valve preventing gas from being discharged from the pressure vessel into the fluid passageway of the discharge tube assembly when the discharge valve is closed, the blast guard valve being capable of opening and closing, the blast guard valve obstructing the fluid passageway of the discharge tube assembly when closed and allowing gas to pass through the fluid passageway when open, the discharge valve and the blast guard valve being operatively connected to each other in a manner such that the discharge valve can open only when the blast guard valve is open, the discharge valve and the blast guard valve being operatively connected to each other in a manner such that the discharge valve opens in response to the blast guard valve being open, the discharge tube assembly is configured and adapted such that the opening of the blast guard valve causes a signal in the form of gas having a positive gauge pressure to reach the discharge valve, the pressure vessel supplying gas having the positive gauge pressure that forms the signal, and the discharge valve is configured and adapted to open in response to the signal, characterized in that the air cannon further comprises a trigger valve being operatively connected to the pressure vessel via a first gas passageway and to the discharge valve via a second gas passageway, the trigger valve being capable of opening and closing, the trigger valve operatively connecting the first and second gas passageways when open and operatively disconnecting the first and second gas passageways when closed, the trigger valve being mechanically actuated by the blast guard valve when the blast guard valve is open in a manner causing the trigger valve to open in a manner creating the signal.