The wall of an oven consists of two layers of insulating bricks. In between the layers there is an air gap. The pressure of air gap will be:

Biochemical Engineering mainly deals with the design, construction, and advancement of unit processes that involve biological organisms (such as fermentation) or organic molecules (often enzymes) and has various applications in areas of interest such as biofuels, food, pharmaceuticals, biotechnology, and water treatment processes. (Source: Wikipedia)