The two airlocks are used for spacewalks by cosmonauts wearing Russian Orlan-M spacesuits. To prevent airborne contamination, high-efficiency particulate air (HEPA) filters, airlocks and cleanroom suits are used. These valves are typically a less expensive alternative to more commonly used rotary airlocks. The top five sections of the Baxter Building are completely airtight; all doors are airlocks. Once they are sealed inside their respective airlocks, Brian begins siphoning out the air. The cars are internally pressurized and are joined by pass-through airlocks. Airlocks have a very similar design, allowing free ingress and egress while also restricting airflow. The caisson had six chambers&colon; two each for dredging, supply shafts, and airlocks. This airfoil is sometimes maintained by use of fabric one-way valves called "airlocks". Airlocks of this type usually have pressure doors as a backup. During normal operation, the containment is air-tight and access is only through marine style airlocks. The resulting positive pressure meant that the boiler rooms were accessible only through airlocks. Suitports carry three major advantages over traditional airlocks. There are two man-sized airlocks, one at ground level, and one at . The blow-thru airlocks feature a low profile with large capacity.