Biosafety level
The U.S. Centers for Disease Control and Prevention (CDC) specifies four levels of biocontainment precautions for biological agents, Biosafety Levels 1 through 4. 

# Rationale
Biocontainment can be classified by the relative danger to the surrounding environment as biological safety levels (BSL).  As of 2006, there are four safety levels.  These are called BSL1 through BSL4, with one anomalous level BSL3-ag for agricultural hazards between BSL3 and BSL4.  Higher numbers indicate a greater risk to the external environment.  See biological hazard.
At the lowest level of biocontainment, the containment zone may only be a fume hood that utilizes HEPA filters.  At the highest level the containment involves isolation of the organism by means of building systems, sealed rooms, sealed containers, personal isolation equipment similar to "space suits" and elaborate procedures for entering the room, and decontamination procedures for leaving the room.  In most cases this also includes high levels of security for access to the facility, ensuring that only authorized personnel may be admitted to any area that may have some effect on the quality of the containment zone. This is considered a hot zone.

# The Levels
Biosafety Level 1 is suitable for work involving well-characterized agents not known to consistently cause disease in healthy adult humans, and of minimal potential hazard to laboratory personnel and the environment. The laboratory is not necessarily separated from the general traffic patterns in the building. Work is generally conducted on open bench tops using standard microbiological practices. Special containment equipment or facility design is neither required nor generally used. Laboratory personnel have specific training in the procedures conducted in the laboratory and are supervised by a scientist with general training in microbiology or a related science. Still considered a cold zone.
Biosafety Level 2 is similar to Biosafety Level 1 and is suitable for work involving agents of moderate potential hazard to personnel and the environment. It differs from BSL-1 in that
- laboratory personnel have specific training in handling pathogenic agents and are directed by competent scientists;
- access to the laboratory is limited when work is being conducted;
- extreme precautions are taken with contaminated sharp items; and
- certain procedures in which infectious aerosols or splashes may be created are conducted in biological safety cabinets or other physical containment equipment. Still considered a cold zone.
Biosafety Level 3 is applicable to clinical, diagnostic, teaching, research, or production facilities in which work is done with indigenous or exotic agents which may cause serious or potentially lethal disease as a result of exposure by the inhalation route. Laboratory personnel have specific training in handling pathogenic and potentially lethal agents, and are supervised by competent scientists who are experienced in working with these agents. This is considered a neutral or warm zone.
All procedures involving the manipulation of infectious materials are conducted within biological safety cabinets or other physical containment devices, or by personnel wearing appropriate personal protective clothing and equipment. The laboratory has special engineering and design features.
It is recognized, however, that some existing facilities may not have all the facility features recommended for Biosafety Level 3 (i.e., double-door access zone and sealed penetrations). In this circumstance, an acceptable level of safety for the conduct of routine procedures, (e.g., diagnostic procedures involving the propagation of an agent for identification, typing, susceptibility testing, etc.), may be achieved in a Biosafety Level 2 facility, providing
- the exhaust air from the laboratory room is discharged to the outdoors,
- the ventilation to the laboratory is balanced to provide directional airflow into the room,
- access to the laboratory is restricted when work is in progress, and
- the recommended Standard Microbiological Practices, Special Practices, and Safety Equipment for Biosafety Level 3 are rigorously followed.
The decision to implement this modification of Biosafety Level 3 recommendations should be made only by the laboratory director.
Biosafety Level 4 is required for work with dangerous and exotic agents that pose a high individual risk of aerosol-transmitted laboratory infections and life-threatening disease  (e.g. Ebola). Agents with a close or identical antigenic relationship to Biosafety Level 4 agents are handled at this level until sufficient data are obtained either to confirm continued work at this level, or to work with them at a lower level. This is a hot zone considering that anybody that contracts a microorganism from a hot zone will most likely die.
Members of the laboratory staff have specific and thorough training in handling extremely hazardous infectious agents and they understand the primary and secondary containment functions of the standard and special practices, the containment equipment, and the laboratory design characteristics. They are supervised by competent scientists who are trained and experienced in working with these agents. Access to the laboratory is strictly controlled by the laboratory director.
The facility is either in a separate building or in a controlled area within a building, which is completely isolated from all other areas of the building. A specific facility operations manual is prepared or adopted.  Building protocols for preventing contamination often uses negatively pressurized facilities, which, if compromised, would severely inhibit an outbreak of aerosol pathogens.
Within work areas of the facility, all activities are confined to Class III biological safety cabinets, or Class II biological safety cabinets used with one-piece positive pressure personnel suits ventilated by a life support system. The Biosafety Level 4 laboratory has special engineering and design features to prevent microorganisms from being disseminated into the environment. The laboratory is kept at negative air pressure, so that air flows into the room if the barrier is penetrated or breached.  Furthermore, an airlock is used during personnel entry and exit.
Biosafety Level 5 does not exist, given that the protocols followed by a Biosafety Level 4 facility are as strict as technically feasible. In popular culture, this level has been referenced. The novel The Andromeda Strain by Michael Crichton, along with the 1971 film of the same name, directed by Robert Wise reference a fictional Level 5 facility. The novel Mount Dragon by Douglas Preston and Lincoln Child also references such a facility, and its measures likely have a similar purpose.

# Biocontainment practices and facilities by country

## Australia
Australia operates three BSL-4 labs. These are
- The Australian Animal Health Laboratory at 5 Portarlington Road in Geelong (VIC).
- The Virology Laboratory of the Queensland Department of Health at 39 Kessels Road, Coopers Plains (QLD).
- The National High Security Laboratory, operating under the auspices of the Victoria Infectious Diseases Reference Laboratory, at 10 Wreckyn St in North Melbourne (VIC).

## Brazil
The Fundacao Oswaldo Cruz, a biomedical research institute of the Brazilian government, operates a BSL-4 in Rio de Janeiro.

## Canada
Canada has one BSL4 facility, located at the National Microbiology Laboratory in Winnipeg.

## France
France maintains a P4 (for "pathogen" or "protection" level 4) laboratory, Laboratoire P4 Jean Merieux in Lyon.

## Gabon
The Centre International de Recherches Medicales de Franceville (CIRMF), a research organization supported by the French government, operates West Africa's only BSL-4 lab.

## Germany
Germany currently has two L4 facilities: one located at the Philipps University of Marburg, Institute of Virology and the Bernhard Nocht Institute for Tropical Medicine in Hamburg. A new P4 lab is currently being built in Marburg and will take over the functions of the old L4 facility there. Also, another P4 lab is planned to be built at the Robert Koch Institute in Berlin.

## Japan
Japan has a BSL4 lab at the National Institute for Infectious Diseases, Department of Virology I, Tokyo; however, currently work in this lab is only performed with BSL3 agents. Japan has also a non-operating BSL4 lab at the Institute of Physical and Chemical Research in Tsukuba.

## India
India's BSL4 lab is High Security Animal Disease Laboratory (HSADL) located in Bhopal, India. It deals with all kinds of zoonotic organisms and emerging infectious disease threats.

## Italy
Italy's only BSL4 lab is at Istituto Nazionale Malattie Infettive, Ospedale Lazzaro Spallanzani, Rome. (National Institute of Infectious Diseases, Lazzaro Spallanzani Hospital.)

## Russia
VEKTOR State Research Center of Virology and Biotechnology, Koltsovo, Novosibirsk region. Other BSL4 facilities available during the Soviet era have been dismantled.

## Singapore
The Defence Science Organization(DSO) National Laboratories operates a BSL-4 facility. With the announced  goal of conducting autopsies during a potential deadly epidemic outbreak, Singapore also has a mobile BSL-4 autopsy facility, perhaps the only one of its kind in the world.

## South Africa
The National Institute for Communicable Diseases, Special Pathogens Unit in Johannesburg, South Africa is one of two BSL4 labs in Africa.

## Sweden
The Swedish Institute for Infectious Disease Control runs Scandinavia's only P4 laboratory in Solna.

## Switzerland
The Institute of Virology and Immunoprophylaxis (IVI) in Mittelhausern is the only publicly known laboratory in Switzerland to be classed as having biosafety level (BSL) 4. This laboratory only deals with animal disease which do not transmit to humans, and is the only P4 facility where complete isolation suits are not used.
A P4 laboratory was inaugurated on February 01, 2007 in the Teaching Hospital of Geneva.

## Taiwan
In Taiwan, two laboratories have BSL4. One is Preventive Medical Institute of ROC Ministry of National Defense, another is Kwen-yang Laboratory () Center of Disease Control, Department of Health ROC.

## United Kingdom
The United Kingdom currently has three BSL-4 laboratories, with another under construction. One is under construction at the National Institute for Medical Research in London, and the other has been built by the Ministry of Defence at Porton Down and is called the Chemical and Biological Defence Establishment. There is also a BSL-4 Laboratory in the Viral Zoonosis unit at the Health Protection Agency's Centre for Infections in Colindale.

## United States of America
The U.S. maintains at least eight Biosafety Level 4 facilities, and is currently planning at least seven more:
Operational Facilities:
- USAMRIID in Fort Detrick, MD ("old building")
- CDC in Atlanta, GA (two buildings operational)
- NIH's BSL-4 lab in Building 41A on the NIH Campus in Bethesda, MD (sometimes operates at BSL-3), never operated as a "hot" BSL4 - training facility only
- NIH's BSL-4 lab at the Twinbrook III building, 12735 Twinbrook Pkwy, Rockville, MD (sometimes operates at BSL-3)
- Southwest Foundation for Biomedical Research in San Antonio, TX
- UTMB's Shope Laboratory in Galveston, TX
- Georgia State University in Atlanta, GA (smaller "glovebox" facility)
- The Division of Consolidated Laboratory Services lab (part of the Department of General Services of the Commonwealth of Virginia) in Richmond, VA (so-called "surge" BSL-4 capacity)
Facilities Under Construction and Planned:
- USAMRIID in Fort Detrick, MD ("new building", in design)
- Boston University's National Emerging Infectious Diseases Laboratory (NEIDL) in Boston, MA (under construction)
- UTMB's National Biocontainment Facility in Galveston, TX (under construction)
- DHS's National Biodefense Analysis and Countermeasures Center (NBACC) in Fort Detrick, MD (under construction)
- DHS's National Bio and Agro-Defense Facility (NBAF), location to be determined in late 2007. shortlisted July 2007; final site selection mid to late 2008
- NIAID's Integrated Research Facility in Fort Detrick, MD (in construction- earliest operational date 2009)
- NIAID's Rocky Mountain Laboratories in Hamilton, MT (in construction - earliest operational date 2009)