Biological hazard

A biological hazard, or biohazard, refers to any biological substance capable of posing a threat to the health of living organisms, particularly humans. These hazards may arise from microorganisms, viruses, biological toxins, or other agents that cause infectious disease or toxic effects. The term is also applied more broadly to any biological material that could harm humans, animals, or the environment. To reduce risk, biohazard warnings and containment procedures are widely employed in laboratories, healthcare settings, and industries handling biological materials.
The distinctive biohazard symbol, introduced in 1966 by environmental-health engineer Charles Baldwin of the Dow Chemical Company, has since become an international standard. It is used across packaging, signage, clinical waste disposal systems, and transport labels to alert workers and the public to potential risks.

Biohazard Warning Standards

In the United States and internationally, the American National Standards Institute (ANSI) provides guidance for the use of biohazard signage through its ANSI Z535 Hazardous Communications (HazCom) standards. These are integrated into regulatory frameworks such as OSHA rules and have been widely adopted by other countries as part of occupational safety legislation.
The colour codes associated with the symbol communicate different levels of hazard:

• DANGER (red/white) – identifies a biohazard capable of causing death.
• WARNING (orange/black or orange/white) – indicates a serious hazard that may cause death.
• CAUTION (yellow/black or yellow/white) – used for hazards that may cause injury but not death.
• NOTICE (green/white) – conveys non-injury messages, such as hygiene instructions or general laboratory policies.

These standards ensure rapid visual recognition and consistency across workplaces handling biological materials.

UN/ISO Classification for Transport

Biological agents are classified for transport using United Nations (UN) numbers:

• Category A (UN 2814) – Infectious substances affecting humans; capable of causing severe, life-threatening disease.
• Category A (UN 2900) – Infectious substances affecting animals only; dangerous but not considered harmful to humans.
• Category B (UN 3373) – Biological substances transported for diagnostic or investigational purposes.
• UN 3291 – Regulated medical waste derived from medical treatment, research, or testing.

These categories govern packaging requirements, handling methods, and international movement of biological materials.

Levels of Biohazard

The United States Centers for Disease Control and Prevention (CDC) classifies pathogens and research facilities according to Biosafety Levels (BSL 1–4). These levels reflect the degree of risk posed by specific agents and dictate the containment, protective equipment, and procedural controls required.
Biohazard Level 1 (BSL-1)Includes agents causing minimal threat to humans, such as Bacillus subtilis, non-pathogenic E. coli, and varicella (chickenpox). Work typically requires gloves and basic protective equipment.
Biohazard Level 2 (BSL-2)Covers agents causing mild human disease or those difficult to contract via aerosols, including hepatitis A–C, influenza A strains, HIV, dengue fever, mumps, measles, and Salmonella. Work may involve diagnostic testing with heightened precautions.
Biohazard Level 3 (BSL-3)Applies to agents capable of causing severe or potentially fatal diseases but for which treatment or vaccines exist. Examples include anthrax, yellow fever, tuberculosis, SARS and MERS coronaviruses, hantaviruses, and Rift Valley fever. Laboratories require controlled airflow, restricted access, and specialised ventilation systems.
Biohazard Level 4 (BSL-4)Reserved for the highest-risk agents with no available treatment or vaccine, such as Ebola virus, Marburg virus, Lassa fever virus, Crimean–Congo haemorrhagic fever virus, Nipah virus, and other viral haemorrhagic fever pathogens. Work is conducted in maximum containment laboratories using positive-pressure suits, airlock systems, multiple decontamination stages, and isolated air and water lines. Currently, no bacteria are classified at this level.

Biological Hazard Symbol and Use

The biohazard symbol is one of the most recognisable hazard pictograms. Its design is intended to be simple, symmetrical, and easily identifiable from a distance. When incorporated into ANSI or OSHA signage, it is accompanied by a signal word (DANGER, WARNING, CAUTION, or NOTICE) and clear instructions or hazard descriptions. In Unicode, the symbol appears as U+2623.

Applications and Procedures

Biohazards are associated with diverse environments including clinical laboratories, hospitals, research facilities, waste-management systems, veterinary clinics, and industrial processing plants. Standard precautions include:

• Proper storage and labelling of infectious materials
• Use of personal protective equipment
• Controlled ventilation and airflow
• Decontamination via autoclaving, chemical disinfectants, or ultraviolet systems
• Secure waste disposal following local and international regulations