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Biological or infectious agents/hazards

Biohazards/infectious substances – characteristics, classification and hazards

A biological hazard, or biohazard, is any microorganism, cell culture or human endoparasite, including any that have been genetically modified, that can cause infection, allergy, toxicity or otherwise create a hazard to human health.

Biohazards arise from exposure to a range of pathogenic organisms. Acute or chronic infectious diseases may be caused by bacteria, viruses, protozoa or fungi. The pathogen can enter the body via skin contact, puncture wounds, cuts, inhalation of aerosols or dusts and also by ingestion of contaminated food or drink.

These pathogens are found almost everywhere in varying forms and exist as a biohazard when the numbers exceed what is regarded as an infective dose.

Pathogenic organisms

Most biohazards arise from single-celled organisms of various types, which are collectively referred to as pathogenic organisms. These can be grouped into four different classes:

  • Bacteria (Escherichia coli (E.coli), tuberculosis (TB), salmonella, legionella, etc.)
  • Viruses (hepatitis B, C, HIV, etc.)
  • Protozoa (toxoplasmosis,, malaria, etc.)
  • Fungi and spores (ringworm, etc.)
  • Prions - transmissible spongiform encephalopathies (TSE's) (Creutzfeldt-Jakob disease CJD)

Included within the above list is a serious health risk to firefighters: the transmission of infectious diseases (zoonoses) through direct or indirect contact with animals that are alive or dead and with animal waste. Examples of zoonoses are rabies and ringworm. Contact between pregnant firefighters and sheep and goats carrying chlamydia psittaci can also result in miscarriage.


  • About 0.01mm in length.
  • Primarily found in moist medium with small hairs used for locomotion.
  • Rapidly increase in numbers in ideal conditions.
  • Not able to withstand high temperatures (above 60° for half an hour will destroy them), and large doses of gamma radiation will kill them.
  • Many bacteria are harmless.
  • Necessary in soil, human and animal bodies

Some can produce toxins and cause symptoms of disease such as TB, anthrax, tetanus or bubonic plague.


  • Much smaller than bacteria, consisting of nuclear material (DNA or RNA – ribonucleic acid) surrounded by complex outer coat of protein.
  • Attach to host cell to reproduce and then infect other cells.
  • Typical viruses include Lassa fever, herpes, influenza, HIV, rabies and smallpox.


Larger, single celled-organisms similar to bacteria.

Often water-borne, including malaria and amoebic dysentery.

Fungi and spores

  • Live as parasites on a host.
  • Examples include thrush, athlete’s foot and ringworm.

Categorisation of microorganisms

The Advisory Committee on Dangerous Pathogens (ACDP) advises the Health and Safety Commission, the Health and Safety Executive (HSE) and appropriate government ministers on all aspects of hazards and risks to workers and others from exposure to pathogens. In 1995 the ACDP issued guidance on the categorisation of biological agents, which classified biological agents into four categories:

Hazard group 1: unlikely to cause disease.

Hazard group 2: can cause disease and may be a hazard to employees, is unlikely to spread to the community and there is usually an effective prophylaxis or treatment available (e.g. measles and mumps).

Hazard group 3: can cause severe human disease and may be a hazard to employees, may spread to the community but there is usually an effective prophylaxis or treatment available (e.g. hepatitis B and tuberculosis).

Hazard group 4: causes severe human disease and is a serious hazard to employees, is likely to spread to the community and there is usually no effective prophylaxis or treatment available (examples include Haemorrhagic fevers (Ebola and Lassa).

The ACDP issues an approved list of biological agents which is updated regularly and available at:


The ACDP has placed a duty on employers to identify hazards in the workplace and to understand and control the infection risk where a hazard group 4 containment exists (based on COSHH principles).

The Management of Health and Safety Regulations 1999 (MHSR99) recommends the appointment of a competent person such as a safety officer/adviser, to assist the employer with:

  • Notifying local authority fire services in advance of substances to be handled that may be a hazard to firefighters in the course of their duties (as part of the emergency plan)
  • Responsibility for decontamination procedures
  • Disposal of infectious waste.

COSHH Regulations require the Health and Safety Executive (HSE) to be notified of the intention to use, store or transport certain hazard groups.


Additional hazards are associated with biological agent research and development premises and may include:

  • High security levels such as including electronic locking mechanisms, preventing unauthorised access
  • Premises containing hazard group 3 and 4 materials are required to maintain negative pressure (up to –100Pa) to prevent the release of biological agents outside the building.
  • An uninterruptible power supplying lab equipment and building facilities
  • Regular disinfection of labs, which generally takes the form of gaseous formaldehyde fumigation over a 36-hour period
  • Various types of animals used for research purposes
  • Gases, including nitrogen, hydrogen, helium and oxygen
  • Chemicals, including acids, bases, alcohols, volatile agents and toxic or carcinogenic organic compounds such as benzene
  • Various radiation sources for tracer experiments
  • Liquid nitrogen for cryogenic storage

Biohazard usage

Biological hazards may be encountered in a wide range of situations:

  • Hospitals (isolation wards, post mortem areas, medical schools, laboratories, etc.)
  • Biotechnology laboratories using genetically modified organisms
  • Universities or colleges
  • Veterinary laboratories, quarantine kennels or abattoirs
  • Government research establishments
  • Biological, medical, animal research establishments
  • Farms, zoos, wildlife parks
  • Sewers, sewage treatment plants and flood water
  • Casualty handling/cadavers at fires, transport incidents or other special service calls
  • Residential premises where people may be infected
  • Post offices and mail delivery couriers
  • Funeral parlours/embalmers
  • Biological warfare or terrorist sites
  • Pharmaceutical laboratories
  • Government establishments

Biohazard transportation, packaging and storage


The transport categories are defined as:

  • Category A: infectious substance transported in a form that, when exposure to it occurs, is capable of causing permanent disability, life-threatening or fatal disease to humans or animals.
  • Category B: infectious substance that does not meet the criteria for inclusion in category A

For all substances a triple packaging system is used. This includes:

  • A primary, watertight and leak-proof receptacle surrounded by sufficient absorbent material to absorb any spills caused by breakage
  • A secondary, watertight and leak proof packaging, again containing sufficient absorbent material to absorb any spills
  • An outer packaging that protects the secondary packaging from physical damage

The outer wrapping of any package should bear the international warning signs and a warning that the package should be neither opened nor touched. On the outer packaging there should be an indication of the nature of the contents, together with the name and address of both the consignor and consignee. These details should also be provided with the package.

For transportation, infectious substances will be assigned to UN 2814, UN 2900 or UN 3373. Vehicles used for the transportation of biological agents will come under UN hazard classification 6.2 and may display the warning triangle for ‘substances containing disease-producing microorganisms’.


Hazard group 4 materials must not be sent through the postal system. Special arrangements apply to their transportation, nationally and internationally.

Hazard group 2 and 3 materials may be transported either by post or by an authorised courier provided they comply with the packaging requirements and bear the international warning signs together with the names and addresses of the sender and recipient.

Organisations that regularly send such materials through the post should have procedures for contacting competent personnel in the event of an accident.

Location and meaning of signs

Many establishments will display the international biohazard sign. However, the use of this sign varies considerably. Other black and white signs may relate to animals (e.g. Do not remove, May be removed in cages, etc.).

Where biological agents are present within a building there should always be a warning symbol present at the entrances to laboratories and refrigeration units for agents of hazard groups 2, 3 and 4, but they may not be found externally.