Biological agents—bacteria, viruses, parasites, and fungi—are divided into four biosafety levels (BSL). Each level pertains to a threat level and the levels ascend in order of increasing threat.

That is to say, level one organisms are the least hazardous, and level four organisms are the most.

This article breaks down the four biosafety levels, explains why we have them, and gives some examples of the kinds of organisms that researchers work on at each level.

Why Do We Have Biosafety Levels?

The idea of formalizing biosafety levels emerged in the United States during the 1960s. It followed the realization that laboratories working with infectious agents needed standardized safety precautions between labs.

These levels have since been adapted in response to emerging infectious diseases and biotechnological advancements.

The dynamic nature of biology research means biosafety levels (and lab safety procedures in general) must be continually evaluated and updated to accommodate new research technology, such as CRISPR gene editing.

When Biocontainment Goes Wrong

In 1977, there was an outbreak of the H1N1 influenza virus reported by the Soviet Union. The cause of the outbreak is suspected to be a leak from a laboratory due to a lapse in biosafety protocols (although there are other suggested causes).

The event highlighted the need for stringent lab biosafety protocols to prevent similar accidental releases of pathogenic viruses. This event resulted in stricter regulations and oversight in handling viral cultures worldwide.

Biosafety Level One

BSL-1 labs house organisms that do not cause disease in healthy persons or are not suspected to cause disease.

Therefore, BSL-1 labs don’t need to be isolated from the rest of the building.

No specific lab equipment, such as biosafety cabinets, is required, and work may be carried out on the bench with standard PPE (lab coat, gloves, and safety glasses).

Decontamination of material with the potential to cause minor infections in compromised individuals, or exacerbate infections, can be done using bleach or alcohol.

Examples of BSL-1 organisms include Aspergillus niger, Escherichia coli strain K12 (your workhorse E. coli lab strain), and Lactobacillus acidophilus.

Biosafety Level Two

BSL-2 labs house organisms that may cause moderate but treatable illnesses that are difficult to spread and contract from aerosols. An aerosol is a cloud of minute droplets, or particles light enough to remain airborne.

Examples of diseases caused by BSL-2 organisms are Lyme disease and influenza.

Because of the elevated risk of infection, access to BSL-2 labs is granted for approved personnel only, and access is controlled via a keypad with an access code.

Only standard PPE is required, but it’s kept in the lab. Sometimes, BSL-2 lab coats may be a different color to those belonging to BSL-1 labs.

All procedures that can generate aerosols, such as sonication, must be performed in a biosafety cabinet.

Decontamination of material that has the potential to cause or exacerbate infections is achieved using an autoclave.

Examples of BSL-2 organisms include Hepatovirus A (Hep A), Staphylococcus aureus, Streptococcus pneumoniae, and Trypanosoma brucei.

Most biological lab work is carried out in BSL-1 and -2 labs.

Biosafety Level Three

BSL-3 labs contain organisms that cause potentially lethal infections, but for which treatments are available. This includes illnesses that are potentially transmissible via aerosols.

Examples of diseases caused by BSL-3 organisms are West Nile Fever and tuberculosis. Many indigenous diseases are caused by agents classified as BSL-3 organisms.

At this level, work and lab access is overseen by relevant government agencies, and is highly restricted.

Workers are typically immunized against the agents they are exposed to and subject to ongoing health monitoring.

As far as possible, procedures are performed in a biosafety cabinet with a HEPA filter, and labs are constructed with features that facilitate air movement, filtration, and laboratory disinfection. Labs are built away from areas that have an unrestricted flow of people.

Non-standard PPE such as overboots, face masks, and extended gowns that tie at the rear are used. Some of these may be discarded after each use.

For BSL-3 work involving animals that cannot be done in a biosafety cabinet, workers must wear full-body suits and respirators.

Examples of BSL-3 organisms include Yersinia pestis (the plague), Severe Acute Respiratory Syndrome-related coronavirus (SARS-virus), and Rift Valley Fever Phlebovirus.

Biosafety Level Four

BSL-4 labs contain organisms that cause potentially lethal infections and for which no licensed treatments are available.

Facilities that house BSL-4 labs are extremely rare. Porton Down is perhaps the most famous example in the UK.

In the US, two famous examples are the National Biodefense Analysis and Countermeasures Center in Maryland and the Centers for Disease Control and Prevention in Georgia.

Diseases caused by BSL-4 include smallpox, Ebola, and hemorrhagic fever. Extraterrestrial samples (rocks—not aliens!) are also housed in BSL-4 labs.

The PPE used in the labs includes positive pressure suits, and the labs have airlocks.

Examples of BSL-4 organisms include Ebolavirus and Brazilian mammarenavirus.

Biosafety Levels are a Legal Requirement

The categorization of laboratories into different Biosafety Levels is not just a guideline but a legal requirement set by various national and international regulatory bodies.

These standards are designed to protect laboratory personnel, the surrounding community, and the environment from potential exposure to dangerous pathogens.

Regulatory Frameworks in the US

In the United States, the Centers for Disease Control and Prevention (CDC) and the National Institutes of Health (NIH) provide the primary framework for biosafety in microbiological and biomedical laboratories.

Labs must adhere to the BSL guidelines outlined in the CDC’s “Biosafety in Microbiological and Biomedical Laboratories” document.

Regulatory Frameworks in Europe

Similar regulations are enforced by the European Centre for Disease Prevention and Control (ECDC) and individual country-specific regulatory bodies.

Each country may have additional guidelines that complement the broader European directives.

Importance of Compliance

Compliance with these biosafety levels ensures:

• Containment. Pathogens are contained in the lab to prevent their accidental release.
• Safety. The lab is a safe working environment for researchers and technicians.
• Community Health. The public and the environment are protected from potentially disastrous exposure to infectious agents.

Consequences of Non-compliance

Non-compliance with biosafety regulations can result in severe consequences, such as:

• Legal action such as fines or lab closure.
• Reputational damage affecting funding and collaborative opportunities.
• Health risks that potentially cause outbreaks of diseases.

To maintain compliance, laboratories are periodically inspected by regulatory bodies to ensure they meet the required safety standards.

Labs that qualify and adhere to a BSL are labeled like in the picture below:

Biosafety Levels Summarized

That was a brief summary of biosafety levels. Now you know what they are and what kinds of organisms belong to each class. And if you already knew that, hopefully, you’ve learned something new about why we have them and the regulatory bodies responsible for updating them.

If you want to check the biosafety level of a given organism, check out this huge table published by Stanford University. For more lab safety information on Bitesize Bio, browse our previous lab safety articles.