Safety means for ventilated closed chambers

Claim 1

IN COMBINATION: ENCLOSURE MEANS HAVING A CHAMBER DEFINED THEREIN AND FIRST, SECOND AND THIRD OPENINGS DEFINED THROUGH SAID ENCLOSURE MEANS, SAID FIRST OPENING ENABLING GASEOUS MEDIA OUTSIDE SAID ENCLOSURE MEANS TO PASS INTO SAID CHAMBER; AN EXHAUST FAN, INCLUDING A ROTATABLE SHAFT, OPERABLE FOR EXHAUSTING GASEOUS MEDIA THROUGH THE SECOND OPENING FROM SAID CHAMBER; A MOTOR OPERABLE FOR ROTATING SAID SHAFT AND OPERATING SAID EXHAUST FAN; A COVER ADAPTED FOR CLOSING THE THIRD OPENING AND THEREBY PREVENTING ACCESS INTO THE CHAMBER; HINGE MEANS FOR SWINGING SAID COVER ABOUT ONE OF ITS EDGES TO PERMIT OR PREVENT ACCESS INTO THE CHAMBER THROUGH THE THIRD OPENING; MEANS FOR BIASING SAID COVER TO A POSITION SO THAT THE THIRD OPENING IS UNCLOSED THEREBY PERMITTING ACCESS INTO THE CHAMBER; A BOLT, FIXED TO A PIVOT PROTRUDING THROUGH SAID COVER, ADAPTED FOR ACTUATION FROM OUTSIDE OF SAID ENCLOSURE MEANS, SAID BOLT HAVING AN ARM EXTENDING THEREFROM; AN UPWARDLY OPEN ANGLE PIECE FOR RECEIVING SAID BOLT WHEN SAID COVER IS CLOSING THE THIRD OPENING; A GUIDE MEMBER UPWARDLY EXTENDING ALONG SAID COVER; A WEIGHT, SLIDABLE ALONG SAID GUIDE MEMBER, ADAPTED, UPON SLIDING DOWNWARDLY, TO ABUT SAID ARM WHEN SAID BOLT IS RECEIVED BY SAID ANGLE PIECE THEREBY ROTATIVELY MOVING SAID PIVOTED BOLT OUT OF RECEPTION BY SAID ANGLE PIECE TO CAUSE SAID BIASSING MEANS TO MOVE SAID COVER TO THE POSITION WHERE THE THIRD OPENING IS UNCLOSED; ELECTRICALLY CONTROLLED DETENT MEANS ADAPTED TO ARREST SAID WEIGHT WHEN SAID WEIGHT IS SLID UPWARDLY ALONG SAID GUIDE MEMBER TO A POSITION CLEAR OF SAID ARM, SAID DETENT MEANS BEING OPERABLE IN RESPONSE TO AN ELECTRICAL SIGNAL TO RELEASE THE ARRESTED WEIGHT THEREBY ENABLING SAID WEIGHT TO SLIDE DOWNWARDLY, BY GRAVITY, ALONG SAID GUIDE MEMBER; MEANS FOR PRODUCING AN ELECTRICAL SIGNAL TO OPERATE SAID DETENT MEANS IN RESPONSE TO THE NON-ROTATION OF SAID SHAFT OF SAID EXHAUST FAN.