Last reviewed 26 June 2013

In this second article of our two-part feature, Dr. Heather Mawhinney considers the safe selection of biocides and their use for the purposes of disinfection.

Introduction to biocides

Disinfectants have become essential products in today’s world, both for industrial and domestic purposes. Biocides are used as a defence against relentless attacks from micro-organisms and pests. They are a diverse and highly specialised selection of chemicals, with specific and essential uses that provide enormous benefits daily, many of which are taken for granted.

Disinfectants are an effective and safe means of eliminating bio-hazards when used properly. However, if used incorrectly, they can be hazardous and may lead to accidents.

Common types of disinfectants

There are many different types of biocides available for disinfectant purposes. Outside the Biocidal Products Regulations (which state there are 23 different biocidal product types), disinfectants can be divided into classes on the basis of their chemical composition or by their activity and how many types of micro-organisms they kill.

Biocides can be alcohols, aldehydes, compounds containing chlorine or iodine, phenolics, quaternary ammonium compounds and oxidising agents. Disinfectants can be classified as low, medium or high-level disinfectants; highly effective disinfectants (sometimes known as chemical sterilants) can kill all micro-organisms, including bacteria, fungi, viruses, spores, (eg glutaraldehyde); medium effective disinfectants cannot kill bacteria spores, but can kill bacteria, fungi and most viruses (eg ethanol); while low-efficacy disinfectants can kill most bacteria, some fungi and viruses, but are not useful against bacterial spores, mycobacterium tuberculosis and certain fungi and viruses (eg chlorhexidine).

Choosing disinfectants

In choosing a disinfectant, the following factors should be considered.

  • Safety: select a non-toxic disinfectant with no residue or corrosion and ensure it causes no secondary pollution. Study the Safety Data Sheet (SDS) to understand the hazardous properties of the disinfectant.

  • Bacterial effect: there is usually greatest demand for a quick and efficient, broad-spectrum disinfectant with low impact to the environment.

  • Economic: ideally, the disinfectant should be of low concentration and price (however, dilute reagents can be costly to transport as they contain a high proportion of water).

  • Operation: the method of use should preferably be simple and convenient.

Chemical hazards associated with disinfectants

Disinfectants can have dangerous properties which are potentially hazardous to workers, eg some are corrosive, irritant, highly flammable, explosive and strongly oxidising. Some chemical disinfectants can also be irritating to the skin, eyes and respiratory system.

Flammability is one of the potential dangers when chemical disinfectants are used. Flammable liquid biocides could be ignited if used near an ignition source, particularly if they are applied as a sprayed mist. In the presence of a flammable substance, explosive and oxidising disinfectants can cause an immediate fire; similarly they can also feed an existing one.

Mixing chemical disinfectants with other chemical substances can be very dangerous and can result in explosions or the release of hazardous gases. Chlorine, which is a toxic gas, is rapidly released from sodium hypochlorite solutions (bleach) if mixed with acids (such as those contained in cleaning agents). Bleach will also react with ammonia (a component of some window cleaners and paint) to release toxic chloramine gases.

Health hazards associated with disinfectants

Biocides can enter the body by three different routes: through swallowing, skin penetration and inhalation, and all of them pose a risk to health.

Health hazards caused by biocides include:

  • skin — dryness, itchiness, allergy, inflammation, burns, sensitisation, dermatitis

  • eyes — redness, swelling, burns, blindness

  • respiratory system — coughing, shortness of breath, asthma

  • nervous system — dizziness, headache

  • other organs — adversely affected liver and kidney function.

Safe use of disinfectants

There should be a well-documented biocide management programme in place which ideally forms part of the overall company safety management system. This will help facilitate effective implementation. There should be adequate resources to develop, implement and maintain such a programme. It is desirable to consider safety and health aspects of the materials, processes and equipment at the design or purchase stage. This will save additional expenses and often reduce practical difficulty in subsequent adjustments to accommodate the safety features.

Competent persons, knowledgeable about the hazards associated with the chemical disinfectants and related processes, should prepare the programme, with assistance from specialists where needed.

To ensure the safety and health of employees engaged in handling disinfectants, risk assessments must be conducted to systematically identify and investigate potential hazards in order to minimise the risk of adverse health and safety effects due to exposure to biocides in the workplace.

The first step in this process is to identify all disinfectants and their associated hazards; an inventory of all workplace chemical substances will aid this task. The risks arising from these hazards must be assessed, considering each case individually, taking into account the work situation and personnel involved (physical and chemical disinfectant properties, work practices, duration of exposure, susceptibility of personnel, etc). The chemical disinfectant’s SDS should provide valuable information for the risk assessment.

Appropriate preventive and/or control measures should then be put in place to eliminate or mitigate the risk to acceptable levels, with their effectiveness being regularly monitored and reviewed.

The following hierarchy of control should be followed when adopting appropriate preventive measures.

  • Eliminate: remove the hazardous chemical disinfectant from the process.

  • Substitute: use an alternative, less harmful, disinfectant for the job.

  • Engineering control: eliminate or lower the risk at source, eg by ventilation, enclosure or isolation.

  • Administrative control: reduce exposure by the implementation of safe systems of work, scheduling tasks, adopting good housekeeping practices, etc.

  • Information, instruction and training: offer both procedural information and instruction, together with related occupational safety training.

  • Personal protective equipment (PPE): carefully select appropriate PPE and use this passive control measure as a last resort and as a supplement to the other more effective control techniques.

Often, a combination of measures will be used, eg ventilation, safe systems of work and PPE. Reference should be made to relevant legislation, codes of practice, guidelines and best trade practices in order to decide on the need and adequacy of safety measures. Management should also keep abreast of the upcoming safety alternatives or devices that are available on the market; the process should be reviewed and updated as appropriate.

Other factors to be considered as part of the biocide management plan include storage precautions, PPE inspection routines, first-aid measures, emergency response plans and health surveillance.

The hazard information and protective measures associated with each biocide should be communicated to all affected employees; the safety and health information on the materials and processes should be disseminated to employees via adequate instruction and training.


For years, people have sought protection against pests and other organisms which threaten their health, food and environment. Biocides, the principal defence against these agents of disease and destruction, are essential in our everyday lives for the purposes of prevention and protection. They have numerous applications and should be handled with care so that their enormous benefits can be reaped.