COSHH Assessments – 7 key questions


In my last post I discussed the main problems that I often encounter with how COSHH assessments are carried out in practice. These were

  • concentrating on the hazards rather than the risks
  • neglecting to include process generated substances
  • concentrating on inhalation exposures and neglecting other routes
  • lack of emphasis on controls
  • failure to consider measures needed to ensure continued effectiveness of controls

To be “suitable and sufficient” a COSHH assessment needs to address the risks associated with the use of hazardous substances and decide on what measures are needed to reduce them to an acceptable level. The best way to achieve this is to base the assessment on the work. COSHH assessments should be focused on the process or task rather than the substance.

Guidance on risk assessments typically outlines a number of key steps as illustrated in the following flow chart




Although this provides a good overview of the process it is a little vague. In particular, it doesn’t really set out what is involved in the crucial third step – evaluating significant risks.

Some time ago, I sat down and tried to work out exactly what I do when I carry out a COSHH assessment. I concluded that I ask myself a series of questions:

  1. What substances are workers (and others) exposed to?
  2. What harm can these substances cause?
  3. Is exposure significant?
  4. What is currently being done to control exposure?
  5. Is that good enough?
  6. What needs to be done to improve control?
  7. What else needs to be done to ensure that adequate control is maintained? (e.g. testing controls, air monitoring, health surveillance, training etc.)

Let’s have a look at these in a little more detail

1. What substances are workers (and others) exposed to?

  • Starting with the task or process work out what substances are present – including both those substances bought in and those generated by the process (the latter often present the most significant risks).
  • Consider who could be exposed and how – i.e. by what routes (inhalation, skin, ingestion, injection)

2. What harm can these substances cause?

  • For substances bought it should be possible to determine the hazards they can present to health by looking at the label on their containers and the safety data sheet that suppliers must provide.
  • Information on process generated substances might be more difficult to locate, but the Health and Safety Executive publications and their website are often a good place to start.

For many people this is the end of the assessment, but if you stop here you have only identified hazards and haven’t addressed the risks. You need to continue to consider the other questions.

3. Is exposure significant?

This is probably the most difficult question to answer! Bear in mind that with hazardous substances the risk can be represented by the following equation :-


So the key is to try and quantify or estimate the degree of exposure. There are various ways this can be achieved, for example

  • personal air sampling
  • use of direct reading instruments
  • semi-quantitative measurements (e.g. direct reading dust monitors)
  • visualisation techniques (e.g. dust lamp or smoke tubes)
  • observations


The methods used will depend on circumstances. Sometimes observation is enough where it is obvious that improved controls are needed.


Whatever methods are used, a judgement has to be made on whether exposure is “significant” or not. Essentially you need to ask yourself “does something need to be done to reduce exposure?”. If the answer is “yes” then exposure is significant. (This is something I’ll return to in a future post)

4. What is currently being done to control exposure?

This question may be combined with the previous one. In most cases a COSHH assessment will be undertaken for an existing process where there are likely to be controls in place. You’ll need to identify what they are.

With a new process, the initial COSHH assessment should be carried out before the process starts. In that case you’ll need to identify what control options are available.

5. Is that good enough?

This may be asked in conjunction with questions 3 and 4. Once it’s been established what controls are available a judgement needs to be made on whether they are reducing exposure to a low enough level.

6. What needs to be done to improve control?

If existing controls aren’t good enough then, clearly, improvements will need to be made. A COSHH assessment should identify what measures are needed to control exposure.

Even where exposure is below exposure limits if there are ways of improving control they should be considered. For example, if personal protection is being used, even if it is adequate to reduce exposure below exposure limits, an attempt should be made to identify alternative controls.

Also if workers are exposed to carcinogens, mutagens or asthmagens, COSHH requires that exposure should be reduced to the lowest level reasonably practicable below any relevant limit. So in such cases it is particularly important to try to identify any additional controls.

7. What else needs to be done to ensure that adequate control is maintained?

This is probably the most neglected aspect of COSHH assessments even though the Regulations are quite explicit in requiring the assessment to consider what measures are needed to ensure compliance with all the regulations.

There are many examples in industry where expensive control measures are installed only for them to remain unused, used infrequently or used incorrectly thereby rendering them ineffective. To overcome these problems, effective management measures need to be put into place. COSHH Regulations 8 to 12 are about the things employers can and should do to ensure the controls they implement continue to work effectively. So once appropriate controls have been identified, the assessor needs to ask:

  • what needs to be done to ensure that the controls are used properly
  • what maintenance and testing is needed to ensure that engineering controls and personal protective equipment continue to operate effectively and what auditing should be carried out to ensure that the procedures and safe working methods are followed
  • is exposure monitoring and health surveillance needed as additional checks that the controls are effective
  • what information, instruction and training is required to ensure workers know why the controls are needed, how to use them correctly, procedures for reporting faults etc.

Published by ms6282

I'm a consultant and trainer specialising in the recognition, evaluation and control of health hazards in the workplace. I'm based in the North West of England, but am willing to travel (almost) anywhere

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