Safety closure means for pressurized furnaces

Claim 1

IN A PRESSURIZED FURNACE HAVING A FURNACE WALL AND AN ACCESS PASSAGE IN SAID WALL, A SAFETY ARRANGEMENT INCLUDING A COVER FOR SAID PASSAGE AND MEANS FOR INJECTING FLUID INTO SAID PASSAGE UNDER A PREDETERMINED PRESSURE AND FLOW TO PREVENT THE FLOW OF COMBUSTION GASES THROUGH SAID PASSAGE TO THE OUTSIDE OF THE FURNACE WHEN SAID COVER IS OPENED, SAID FLUID BEING INJECTED SO AS TO PRODUCE A PRESSURE GRADIENT IN SAID PASSAGE FROM A NEGATIVE PRESSURE ADJACENT SAID COVER TO A POSITIVE PRESSURE IN SAID FURNACE, THE COMBINATION WITH SAID COVER OF A SAFETY DEVICE COMPRISING A TUBULAR MEMBER CONNECTED AT ONE END TO THE ACCESS PASSAGE TO EXPOSE SAID ONE END TO A RESULTANT PRESSURE WHICH IS EQUAL TO OR LESS THAN ATMOSPHERIC PRESSURE, SAID TUBULAR MEMBER EXTENDING OUTSIDE SAID FURNACE AND HAVING ITS OTHER END EXPOSED TO ATMOSPHERIC PRESSURE, AND MEANS AT SAID OTHER END TO SHOW THE RELATIONSHIP BETWEEN SAID RESULTANT PRESSURE AND ATMOSPHERIC PRESSURE, THE SHOWING OF A PRESSURE AT SAID OTHER END GREATER THAN ATMOSPHERIC INDICATING AN UNSAFE CONDITION FOR OPENING SAID PASSAGE.