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Chemical Safety

Carrying out COSHH Assessments

The purpose of carrying out a COSHH assessment is to determine if you have taken sufficient steps to eliminate or control the risks, or if there is more you can do to ensure the safety of those working with hazardous substances.

The COSHH form contains drop down fields that will aid with the decision making process; but in all cases, if you need further advice please contact Health, Safety and Wellbeing for support.

This form is not suitable for carrying out assessments of multiple chemicals used in experiments, etc. A different process is in place for this purpose.

When preparing to conduct your assessment you need to bear in mind you are assessing the users' interaction with the hazard (in this case the substance) in order to determine how this risk can be eliminated or minimised. The risk only occurs when this interaction takes place.

Start by gathering any information or data you are likely to need, such as the Safety Data Sheet (SDS). suppliers have to provide this information to you and it can be in paper format or electronic. Make sure you have the most up to date safety data sheet before you attempt your assessment.

Remember, the safety data sheet provides valuable information about the substance, but it doesn't provide you with information about the unique way you will use and interact with the substance.

You should use the COSHH Assessment form to record your assessment.

Start to populate the form with details about:

  • where the product will be used
  • what quantity will be used
  • the frequency of use - daily, weekly, etc.
  • the duration of use - minutes, hours, etc.

What is the nature of the hazard - i.e. dust, mist, fume, splash, solid or more than one of these?

What is the likely route of entry into the user - inhaling dust, mist or fume, splashing onto the skin or in the eyes, swallowing the product by splashing or hand to mouth contact, puncturing the skin, etc?

Who and how many people are likely to be affected. Is it staff, students, visitors, contractors, public, or several of these groups? How many people are likely to be exposed to the risks?

To identify the hazards, think about how you will use and, therefore, interact with the substance.


  • preparation to use, e.g. mixing, decanting, etc.
  • planned use
  • accidental contact - e.g. not washing hands after handling
  • storage requirements
  • accidental spillages
  • other substances produced (by-products)

You may find it easier to split the assessment into tasks appropriate to the hazard, so you might need more than one assessment.

For example, diluting a concentrated substance in preparation for later use is likely to be more hazardous than its planned use and may be conducted by different groups of people.

Your process may produce by-products from the use of the substance and these will also need to be assessed. The SDS is unlikely to give you any information about these, so you may need to look elsewhere for this information.

For example - wood dust will be produced when cutting wood. Information about this can be found from sources such as the HSE's website.

Hazard Statements

Check is whether the product has any Hazard Statements listed against it.

You can do this by looking at the Safety Data Sheet (SDS).This will list the hazard statements applicable to any of the substances used in the product or mixture.

The hazard statements were introduced to replace the previous R-Phrases. The transition period for introducing this change ended on 1 June 2015 (1 June 2017 for mixtures currently in use). Suppliers are required to update their SDS to reflect this information, so make sure you have the up to date SDS before attempting your assessment.

However, some data sheets will still only quote the R-Phrase until later in 2017. If there are only R-Phrases on you data sheet, you can look up the equivalent H-Statement on the internet.

The H-Statements are divided into 3 categories:

  • Physical hazards: H200-290
  • Health hazards: H300-373
  • Environmental hazards: H400-420

There are some additional EUH hazards that were included because there was not a direct equivalent for the old R-Phrase. These have been included in the drop down fields on the form.

Once you know the H-Statements for your substance, choose it/them from the drop down fields on the form.

Then, depending on which H-Statements you have selected, you may need to take further action, as indicated by the results on the form.

E.g. a separate DSEAR assessment will be needed for H-Statments H200-272 and EUH001-044; and health surveillance will be needed for H-Statements H317 & H334 (previously R-Phrases R42 & R43).

In each of these cases you should contact Health, Safety & Wellbeing, who can provide specific advice and support.

If there are no H-Statements or R-Phrases listed against your product, select none from the drop down fields, but continue with your assessment to determine what practical precautions you can introduce to maintain the health and safety of the users.

Many assessors find the subject of WEL's confusing. However, it doesn't need to be and we are here to help.

Only 500 substances have an assigned WEL, so you may find that there is nothing listed for your substances.

The WEL is the workplace exposure limit set in EH40 (the HSE's guidance document) for the particular substance. The form includes a link to the document as the exposure limits are updated based on new information.

You should always consult EH40 for the workplace exposure limit, rather than your Safety Data Sheet (SDS) as EH40 contains the most up to date information and your SDS may be older and out of date.

Once the WEL has been found, list the 15 minute or 8 hour limits, depending on whether you are using the substance for a few minutes or several hours per day. The WEL is quoted in ppm and mg/m3; list them both in case we need to make a judgement on the likely concentration in air, or carry out monitoring for you.

The form enables you to choose whether you are confident that the WEL will not be exceeded during use. For example: the quantity used is very small and the room volume is very large; the WEL might be exceeded and you need monitoring carried out; of you are just unsure and need further advice

If you are in any doubt at all, we can help you with this.

At this stage you need to decide if there is a safer alternative substance that can be used instead of the more hazardous one.

If yes, replace with the safer alternative and re-start your assessment. If no, continue with your assessment.

There may be some circumstances where the alternative that exists is not suitable for the application and you need to carry on using the substance you are assessing. Reasons could include: the substance won't give a satisfactory result; the substance won't reflect what is used in industry and, therefore, won't give the student representative experience; or the cost is too prohibitive. In these cases the form allows you to record your rationale and continue with your assessment.

This section allow you to detail the interaction you/others will have with the substance, so that you can identify how you will eliminate or control this risk.

In the table, under the heading "how could the activity result in contact" you should detail the specific activities that could cause the user to come into contact with the substance.

So, for example, you could identify that dust will be released when mixing powder with water; or perhaps the user could be exposed to spray mist when spraying the substance, etc. The information you include here must be specific to the activity taking place, and not just copied from the safety data sheet.

This will then allow you to choose risk controls specific to the risks you have identified.

When you choose your risk controls, you should do so considering the hierarchy listed below:

  • Can you eliminate the risk altogether - do you need to use the substance at all?
  • Is there a safer form of the substance, e.g. using a paste rather than a powder?
  • Can you change the process or working methods to emit less of the substance or prevent contact with it?
  • Can you enclose the process so that the product does not escape or extract any emissions at source?
  • Can you reduce exposure by having as few people exposed as possible?
  • What PPE can you provide to reduce or prevent exposure? Remember that PPE should always be a last resort as it relies on people to choose to wear it, wear it properly and look after it.

Once you have detailed your risk controls you are able to score your risks using the standard risk assessment score system. This will allow you to detemine if you have got proper control of your risks or whether there is more you can do to ensure the safety of the substance user/s.

In order for the substance user to work safely and know what risk controls they need to use, you should produce a User Information Sheet.

This can be the sheet in the COSHH Assessment Form or, if you already have a written system of work or work instruction, alternative formats can be used. The important thing to ensure is that the substance user is provided with sufficient information to enable them to work safely.

It is never acceptable to give the user the safety data sheet as this only contains information about the substance in its "as supplied" form and gives no information about the unique way in which it will be used.

The User Information Sheet details the training requirements; any written safe working procedures; your unique storage/disposal/spillage procedures; and the correct personal protective equipment to use. In addition, it details the first aid action to take in the event of accidental contact.

If you need to arrange disposal of hazardous chemicals, you can find out more information and contact Estates via the link below.

Once you have completed your COSHH Assessments you will need to update your risk assessment tracker with the assessment information.

The COSHH assessment should be reviewed annually or if changes to substances, work methods, or new personnel are introduced.

Further advice and support can be obtained from Health, Safety & Wellbeing in respect of carrying out COSHH Assessments.

The Classification, Labelling and Packaging Regulations introduced changes to the way substances are classified, labelled and packaged for your use. They introduced a common set of hazard criteria, which improves consistency in the approach to information supply.

The leaflet below details the terminology changes, new pictograms you can expect to see and the hazard/precautionary statements that will apply to substance and can be found on the safety data sheet.

CLP Regs Guide