COSHH / COSHH Risk Assessments

        COSHH Risk Assessments


COSHH Risk Assessments 

Environmental Science has the expertise to advise and support businesses who find they have to undertake assessments of the risk to the health of their employees and people who may be affected by any work activities that use hazardous chemicals and materials. 

Employers must:

Work out what hazardous substances are used in the work place and find out the risks from using these substances to people's health.
Decide what precautions are needed before starting work with hazardous substances.
Prevent people being exposed to hazardous substances but, where this is not reasonably practicable, control the exposure.
Make sure control measures are used and maintained properly and that safety procedures are followed.
If required, monitor exposure of employees to hazardous substances.
Carry out health surveillance where assessment has shown that this is necessary or COSHH makes specific requirements.
If required, prepare plans and procedures to deal with accidents, incidents and emergencies.
Make sure employees are properly informed, trained and supervised.

Unlike other risk assessments, a COSHH assessment indicates that there is either a risk or there is only a minimal risk.  If there is a risk, the employer is required to put in place systems and procedures to reduce the risk to as low a level as possible. 

ESL has specialist advisers who can assist with COSHH assessment and offer guidance on suitable control measures. We can even compile your COSHH Report for you using the HSE COSHH Essentials method, but to do this we need some basic information.  To get things started we have developed a questionnaire that asks for the following information:

The name by which the process is known. You may also be asked to provide a description of the process from a list, but if an appropriate description is not available ‘Other’ can be selected.
The total daily exposure time in hours and/or minutes for each material (see also Information on the Material Required) 
For any materials which are a component of a mixture, the percentage of the mixture made up by that material. (See Mixtures and Solids with Liquids on this page)
For a solid material how dusty it is (High, Medium or Low) (see Dustiness) 
For a liquid the maximum process temperature and either its boiling point or its vapour pressure together with the reference temperature for that vapour pressure. The boiling point or vapour pressure/reference temperature should be available from the data sheet for the material, but could be found from other references. 

About the Process (COSHH)

A COSHH assessment is concerned with any process involving hazardous chemicals in which anyone involved with the process could be exposed to the hazards. The process may be simple or complex and may involve only a single hazardous material or many. For example a single chemical might be used in a polishing or cleaning process, or a more complex process might involve adding different chemicals (perhaps solids and liquids) to a reactor in very different quantities and perhaps at different times and temperatures. It is important when performing an assessment to determine exactly what exposure is involved with each chemical. 

Remember with different chemicals being added to a process at different stages there could for example be exposure to one or more liquids added in significant quantities but over a short time period and exposure to a solid being added in small quantities but over an extended period. These could probably all be included in the same process and the system will determine what control measures are appropriate to address the most hazardous exposure. In other cases it may be necessary to break a complex process down into sub processes which can be individually assessed. For each chemical involved in the process the temperature to be entered is the maximum temperature at which exposure to that chemical arises. 

Risk Phrase R68 (H341, H351, H361)

If any of the materials selected have been assigned risk phrase R68 you will be asked to identify whether the phrase was listed on its own on the safety data sheet or whether it appeared as Muta Cat 3 R68.

Information on the Material Required 

Firstly we'll need to know what the physical properties are for any material used in a given process. For solid materials the appropriate description of its dustiness, for a liquid, the maximum process temperature applicable to the exposure to that material and either its boiling point or its vapour pressure and corresponding reference temperature For each material used in the process you will need to provide the total daily exposure time in hours and minutes as appropriate. Note that the time may not be the same for all materials. 

If any of the materials are components of a mixture then you will need to give us the percentage of each substance within the material. If the solid has an appreciable vapour pressure tell us this pressure and reference temperature as for a liquid. Be careful to use the correct units to correspond with those quoted on the safety data sheet or other reference. 

Repeat for each material after which you should carefully review your data.

About Mixtures

Any of the materials used in a process may themselves be a mixture of one or more chemicals which has been created in a separate process. If a safety data sheet or classification data is available for the sub-mixture as a whole, then that data should be supplied. However if data is only available for the components of the sub-mixture, data will be needed for each component to carry out the assessment and the percentage (by volume or weight) of the total mixture and sub-mixtures given for each component during the assessment. 

Note that the total of the percentages may be less than 100 if the mixture includes any non hazardous materials such as water. If the process involves exposure to more than one mixture of chemicals, for example two separate mixtures are being added to a reactor, then the percentages required are those of the components of each mixture, not of the resulting weight or volume in the reactor. In this situation the total of percentages given during the assessment could exceed 100.

Solids in Liquids

A material used in a process being assessed may consist of a solid (or more than one solid if it is a mixture) dissolved or suspended in a liquid, the solution or suspension having been created in a separate process. A safety data sheet will be required for each hazardous component. However exposure to any of the solids involved through inhalation of dust will not be relevant to the solution or suspension and regardless of how dusty the solids are themselves.

Volatile Solids 

A limited number of solids have an appreciable vapour pressure and exposure by inhalation of the vapour is more likely to be relevant than exposure to dust. When assessing a process involving such a solid you should provide the maximum process temperature, vapour pressure and corresponding reference temperature. this data should be available on the relevant Safety Data Sheet. 

How Much ? Material

The degree of harm which may be suffered from exposure to a hazardous chemical will depend on the quantity involved. During a COSHH assessment using the COSHH Essentials type method you will be asked to select Large, Medium or Small to describe this. Large would correspond to tonnes or tons for a solid, cubic metres or gallons for a liquid, medium to kilograms or pounds for a solid, litres or pints for a liquid, small to grams or ounces for a solid, millilitres or fluid ounces for a liquid. If there is any doubt about which description is appropriate you should choose the higher level. 


The likelihood of inhaling a solid hazardous chemical depends on how easily it can get into the air and this can be judged by assessing how inherently dusty the solid is. During a COSHH Essentials type assessment involving a solid you will be asked to indicate High, Medium or Low to describe its dustiness. High would typically be used to describe fine powders which create dust clouds in use which take several minutes to settle out. Medium would describe crystals or granules which create dust in use but the dust settles out quickly and remains on surfaces. Low would describe solids in lump or pellet form which do not break up and which create little dust. If there is any doubt about which description is appropriate you should choose the higher level. 


The likelihood of inhaling a liquid hazardous chemical depends on how easily it can get into the air which is determined, among other things, by how much vapour it produces. During the assessment this will be determined from the maximum process temperature involving the liquid in question, and either its boiling point or its vapour pressure at a particular reference temperature. The data should be available from the safety data sheet or from other sources and should be given, taking care to make sure that the units you give us for both temperatures and vapour pressure are those quoted by the reference source. (See also Volatile Solids and Units).


The standard units, used by ESL, for temperatures and vapour pressures for liquids and volatile solids are normally set as °C and kPa and you should ensure that any values given to us are expressed in these units. If you express pressure or temperature values in any other units then please be careful to mark these as such. 

Reference Data for COSHH Assessments

You will need to provide the name of the process which has been assessed and a user reference for the assessment. These two items are obligatory. A date for review of the assessment may be also be set. Other references such as to a to the department involved may also be given.

The COSHH Report

The COSHH Report or results sheet provides the following information:

The name of the process which was assessed as entered by the user.
A list of the materials identified as being used in the process together with, for each material, the applicable Risk Phrase numbers and the data entered for that material such as quantity used etc. Note that the materials are listed in descending order of the contribution which each material makes to the exposure risks and therefore to the scale of the measures needed to control the risks. Thus when considering what might be done to reduce the risks and hence the investment in control measures it may be helpful to look at the materials in that order, for example alternative materials, smaller quantities, lower temperatures, shorter process times etc
The nature of the control measures indicated. This follows the HSE COSHH Essentials terminology, i.e. from General ventilation at the lowest level, through Engineering control and Containment to a Special category which indicates that the risks are such that generalised advice is not adequate and specialist advice should be sought.
The number(s) of the HSE COSHH Essentials ‘Control guidance sheets’ which from the information entered are the most relevant to the circumstances of the process. These sheets give advice on appropriate control measures ranging from general advice applicable to the control measure indicated, to more specific advice if you've identified a particular process type. Access to these sheets is available on the HSE website ( or as embedded links for reports in electronic form.
Administrative details of the assessment, date, reference etc. Also included are details of the control measures implemented, the PPE provided, a date for review of the assessment (which can be flagged by us), and other information about the assessment which your may consider relevant.


Actions Following a COSHH Assessment

The results obtained from a COSHH assessment, are only the first stage in enabling you, the employer, to meet your obligations under the regulations, that is to provide the information needed, which together with information provided by the safety data sheet, will enable you to make a valid decision about what you need to do to prevent or adequately control the exposure of your employees to hazardous substances. An awareness and understanding of what is required by the regulations is necessary to make such decisions. In addition to the regulations themselves there are many publications which can assist and some of these are listed on the HSE website.

The overriding aim is to remove the source of the exposure completely if at all possible. If this is not possible then the aim should be to reduce or control the exposure, and only after all such measures have as far as possible been invoked, should personal protective equipment be specified.

Removing the source of the exposure

Removing the source of the exposure will usually mean replacing one or more of the materials involved in the process assessed by a non, or at least less hazardous material. An ESL COSHH report sheet lists the materials in descending order of the contribution made to the exposure which may help the assessor to focus on which material or materials to consider for replacement.

Reducing the exposure

Reducing the exposure may be achievable by any of a number of measures. These include using less of a material, using it in a different form such as a solid in pellet form rather than as a powder, using a lower process temperature if the exposure is to the vapour from a hazardous liquid, or reducing the process time and hence the duration of exposure. 

Again the order in which the materials are listed on a COSHH Report (result sheet) may assist.

Controlling the exposure

Control of exposure can take many forms, ranging from simply ensuring adequate general ventilation to very stringent containment and control of processes. 

The general nature of what should be a suitable form of control is indicated in the COSHH Report sheet following the COSHH Essentials terminology, and the more specific control guidance sheets contained within COSHH Essentials are also identified. Access to these sheets is available on the HSE website ( and the guidance sheet number referred to on the electronic version of the COSHH Report is embedded as an active web link. It is most important to note that if the assessment has resulted in ‘Special’ being identified as a control measure, then specialist advice should be sought as described in control guidance sheet 400. 

In arriving at a decision about the measures needed to address the exposure of employees account also needs to be taken of the risks posed by the physical/chemical properties of any of the materials involved such as flammability (the requirements of the Dangerous Substances and Explosive Atmospheres Regulations may need to be considered), and the degree of risk they may pose to the environment. 

The employees involved must be informed of the results of the assessment.

The introduction of any changes to the materials being used or to the process, and any control measures deemed necessary must be properly planned, including training as necessary.

If personal protective equipment (PPE) is to be used this must be selected as being appropriate for the purpose and employees trained as necessary in its use.

The effectiveness of any measures introduced should be assessed and if necessary monitored on an on-going basis. This may require some form of exposure monitoring to ensure that exposure levels have been adequately reduced. The need for on-going exposure monitoring needs to be considered, notably if the safety data sheet shows that any of the materials involved have a Workplace Exposure Limit. Similarly the need for health monitoring may need to be considered. Once again ESL can provide such a monitoring service. 

Arrangements need to be made to ensure that any equipment, both control measures such as local exhaust ventilation and PPE, are maintained in a condition such that they continue to provide the protection needed.

The assessment should be reviewed from time to time to ensure that it remains valid, bearing in mind that the data associated with hazardous substances is updated regularly. It should also be reviewed if there is any change to the materials being used, or to the process itself. Any employees commencing work with the process must be informed of the assessment and given training as appropriate.

The above is only a brief summary of what needs to be considered following a COSHH assessment. Further information is available from the HSE regulations and guidance notes.


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