One plant experienced an emergency situation. The emergency procedures specified: Close the oxygen feed valve. The oxygen control valve was normally closed by bleeding air out of the valve bonnet diaphragm (air to open). The bleed line was opened and was noted on the control panel. The air, however, did not bleed off through the bonnet vent because a mud dauber wasp constructed mud cells over the vent valve was open, as indicated on the control panel, the air could not escape.