BSL-4 laboratories: highest levels of safety and protection

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.

To leave the lab, laboratory staff in their protective suits pass through the airlock chambers again, though there is an additional step they must take: A chemical shower disinfects the suits for several minutes, followed by hot water and soap. This includes a disinfectant dunk bath for the soles of the overshoes or boots and ensures that there are no more biological agents left on the suits before leaving the laboratory. Materials such as sample containers are also sterilized if they are brought into the laboratory.

Needless to say, any item that is no longer needed cannot simply be thrown away. Any work equipment must be safely discarded. This is done by thermal sterilization treatment in pass-through autoclave systems. Material that must be disposed is placed in the autoclave inside the laboratory. The system sterilizes all objects using a combination of pressure, heat and water vapor (steam). Many medical and laboratory devices are not damaged during this procedure and can be reused. This process inactivates biological samples to where they are then unable to cause an infection.

But there is more that happens behind the walls of the laboratory: Breathing air, water, and liquid waste must also be filtered or sterilized, respectively. HEPA (high-efficiency particulate air) filters are used to clean the air. They are composed of a mat of randomly arranged fibers. These fibers are typically comprised of fiberglass that can trap airborne particles. Liquid waste like water is also subject to chemical or thermal sterilization.

In the real world, work in a BSL-4 lab is evidently not nearly as glamorous and heroic and much less prone to error than television would have us believe. In fact, it is shaped by countless tight security measures that must be taken to safely handle dangerous pathogens, such as Ebola or Marburg virus.