for clarity the assembly shown in fig8 includes three abocs comprising first aboc 10 a positioned on top of second aboc 10 b which is positioned on top of third aboc 10 c this array of abocs is positioned on top of blowout container boc 82 as may be one of a number of typical such bocs in the field one gate valve 84 may be positioned between the boc assembly and wellhead 86 shear spool 88 forms a primary component of boc 82 all of this assembly surrounds drill pipe 22 as shown a second gate valve 90 is positioned in what is referred to as the u201c dead man position u201d at the top of the wellhead superstructure 80 other arrangements and numbers of abocs and bocs are anticipated reference is finally made to fig9 which provides one example of a system for facilitating the placement of back pressure against the outside wall of the bladder assembly of the aboc of the present invention fig9 shows a first aboc 10 a and a second aboc 10 b stacked as referenced in part in fig8 back pressure assembly 100 is generally constructed with flanged outlet 102 into a lower spool of the wellhead superstructure 80 assembly this conducts the pressure of the drilling or production fluids to hydraulic valve 104 and through right angle fixture 106.