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Risk Assessment

Containers recovered on Branscombe beach from MSC Napoli

Chemicals provide society with a wide range of benefits, such as increased agricultural and industrial productivity and improvements in the control of disease. However, chemicals have the potential to cause ill-health and damage to the environment, in their manufacture, use and disposal. Risks to humans from exposure to chemicals are a complex issue.

What is Risk?

Risk = Probability x Consequence

Risk is defined as the probability that a substance or situation will produce harm under specified conditions. Risk is a combination of two factors:

  • The probability that an adverse event will occur (such as exposure from a chemical incident)
  • The consequences of the adverse event (such as how ill that chemical could make you)

A risk may have a high impact but a very low probability of happening.  For example, if you are planning walk to your local shops you wouldn’t usually worry about being involved in a chemical incident. It could potentially be quite serious if it did happen but quite unlikely. You might worry about it raining because it is more likely to happen and affect you getting wet.

The way risks are assessed is to rate their impact and their probability as low, medium or high, as shown on the matrix below.  The numbers are multiplied together to give a score; the higher the score the greater the requirement to address that risk.

Risk Matrix

Risk matrix


Impact of chemical incident is High (3) and the probability is extremely Low (1) then the overall risk is 3 x 1 = 3.  If the impact of it raining is also High (3) and the probability is High (3) then the overall risk is 3 x 3 = 9.  It makes sense to worry more about the raining, which is a much bigger risk.

Risk Assessment

Risk assessment is the process of estimating the potential impact of a hazard (such as a chemical) on a specified population under a particular set of conditions and for a certain timeframe.  Classical risk assessment is based upon 4 stages, namely hazard identification, hazard characterization, exposure assessment and risk characterisation.

Risk assessment is also intended to provide information to all parties concerned so that the best possible decisions are made.  However, there are uncertainties related to risk assessment and it is important to make best possible use of available information.  Issues to consider may include:

  • Risks at a certain point in time as well as changes in risk over time
  • The use of Health Guidance Values (the level of the chemical, for example in air or water, to which people may be exposed without appreciable adverse health risk) which will adequately protect public health
  • Assessments of new types of risk
  • Assessments of different types of risk
  • dentification and comparison of different factors that affect the nature and magnitude of the risk
  • Ranking issues according to their level of risks
  • Provide a clearly documented and open process
  • Consistent, transparent review and recording of public health risks (adapted from EHRA, 2002)

In deciding to undertake a risk assessment the following points must be considered:

  • What is the concern?
  • Why it is a concern?
  • How urgent is the concern?
  • How do the public and other organisations perceive the concern? (P/CCRARM, 1997)

There are many models of risk assessment to suit the many contexts in which risk assessments are undertaken.  It is important that assessors, users, regulators and members of the public recognise risk assessment may not always provide a compelling or definitive outcome.

What is Risk Management?

Effective management of exposure to a variety of chemicals has become a very important public health issue.

“Risk management is the process of identifying, evaluating, selecting, and implementing actions to reduce risk to human health.  The goal of risk management is scientifically sound, cost-effective, integrated actions that reduce or prevent risks while taking into account social, cultural, ethical, political and legal considerations” (P/CCRARM, 1997).  It involves balancing the benefits such as a higher standard of living against the risks associated with exposure to potentially harmful agents such as carcinogens.

Cvenn diagram about risk

(Adapted from P/CCRARM, 1997)

Risk Perception

Risk perception is ones opinion of the likelihood of risk associated with performing a certain activity or choosing a certain lifestyle. Our perception is risk is often influenced by whether we feel in control of a perceived risk.  For example we may choose to smoke, knowing the associated risks, but may be angered by having a perceived risk imposed upon us such as a nuclear power plant.  Whereas, true risk (a scientifically evaluated risk) would evaluate smoking as a higher risk activity. Risk perception can be influenced by lack of information or misinformation leading to an increased risk of a certain situation.  It is important to consider the choices people have in making decisions about risk.

Communicating Risk

Risk communication occurs whenever there is an exchange of information among interested parties about the nature, extent, significance or control of a risk.  Information on risk can be communicated in many ways including media reports, warning labels and public meetings. 

There is an increasing importance being placed upon ‘green issues’ both by local communities and the Government.  This includes environmental concerns from past, present and future industrial activities.   Risk communication is an interactive process of exchange of information and it is important that all parties, especially the public, are involved in order that it is clear why risk assessment is needed.

Role of Chemical Hazards & Poisons Division

The Division in conjunction with other agencies carry out or review environmental health risk assessments including:

  • Determining whether there is any potential public health implications from industrial processes
  • Site investigation reports for identified areas of contaminated land
  • Ongoing public health issues (such as drinking water contamination)
  • Public health implications from chemical incidents (such as spillage of a chemical tanker)
  • Participating in chemical incident exercises


  • Environmental Health Risk Assessment: Guidelines for assessing human health risks from environmental hazards: June 2002
  • Framework for Environmental for Environmental Health Risk Management: The Presidential/Congressional Commission on Risk Assessment and Risk Management, 1997.
  • Handbook of Environmental Risk Assessment and Management, Calow, 1998.