The (official) number of biosafety level 4 (BSL-4) facilities around the world is limited. Nevertheless, they are very popular in movie or television settings, usually featuring scientists in full-body pressurized protective suits who work with highly infectious deadly pathogens that, despite all caution, manage to escape and become the main cause of disaster or the scientists frantically try to find a way to prevent a catastrophic outbreak.
To prevent infectious biological materials from escaping in real life, BSL-4 laboratories are subject to countless safety and security measures. It all starts with the right protective lab equipment and clothing. Before scientists enter the lab, clothing is put on in successive sealed airlock chambers. Street or personal clothes must not be worn inside the laboratory. The employees must take them off and – after a decontamination shower in the airlock - put on special undergarments before dressing in pressurized protective suits. Wearing these full-body protective suits for any length of time can be physically exhausting as they restrict movement and – depending on the material – can be very heavy. That’s because they not only have to successfully protect the wearer, but must also stand up to chemicals, disinfection, abrasion, wear and tear.
The suits protect against direct contact with sample material and, as a result, eliminate the risk of smear infection. They are also supplied with fresh, filtered oxygen from the outside and are under constant positive pressure. In case of damage to the suit, this ensures that no laboratory air that contains highly transmissible airborne pathogens can enter. The gear also includes two pairs of gloves. The outer pair is tightly attached to the suit.
While the air pressure in the safety suits is positive to prevent pathogens from getting inside and keeping them away from the user, the lab is kept under negative pressure (lower than the other lab premises). The laboratory’s walls, ceilings, floors and airlock security doors are airtight. As long as negative pressure is maintained, this measure prevents pathogens from escaping the lab and being released into the atmosphere in case of minor damages to the outer layer or seals. This hermetically sealed setting also facilitates safe disinfection with gases.
From an architectural perspective, the laboratory is never directly connected to the exterior wall of the building. There is always another corridor or other space in between that separates the laboratory from the outside world.