COSHH Explained

Carrying out a COSHH (Control of substances hazardous to health) Assessment for chemicals/substances on a construction site is vital, untrained workers can easily be injured or cause others to be injured. A typical sequence of a COSHH assessment is as follows:-

  1. Assess the risks:-
  • Here you must use all possible information available to assess the use of hazardous substances and substances created from your activities.
  • The starting point is the MSDS or material safety data sheet; this is the product substance information that has been compiled by or for the manufacturers of the particular product.
  • The material or product safety data sheet should contain the chemical/substance ingredients and percentage of the overall product, Risk and Safety Phrases, and on occasion CAS (American Chemical Society classification number). The sheets should include exposure limits, first aid and fire fighting information, as well as the important spillage and disposal information.

Assessing the risks from substances will involve you making a decision that would be affecting someone’s health. The following items should be considered:-

  • How much of the chemical/substance would be used and or produced by the work, and how would people be exposed to it (inhalation/skin contact for example).
  • Just who could be exposed to these and the duration that they could be exposed. It’s well worth considering not only workers, but importantly young and inexperienced persons as well as pregnant woman. For example, Risk Phrases for pregnant women should be noted on any material safety data sheet that contains chemicals/substances that can cause unborn children health problems. The Risk Phrases for pregnant women are R61 to R63.
  • As you have already determined, anyone doing an assessment must have knowledge of the hazards and the risks involved. They should also understand how the work activities will use or produce these, be able to use experience to make the correct decisions concerning these risks, and know the precautions involved in these processes.
  1. Decide what precautions to take:-
  • When the initial assessment has been carried out, or if significant risks are identified prior to any assessment, then action is required to reduce or remove the risks to an acceptable level. This can be done by finding a substitute chemical/substance that is far less hazardous or by following guidance as set out in the next 6 steps.
  1. Prevent or control exposure:- 
  • Prevention to exposure must be considered and if it’s practicable, then consider changing the process/s so that the hazardous chemical or substance is either not required or that the generation of any hazardous chemical/substance is no longer generated.
  • Check to see if the chemical/substance can be substituted or used in a different form, for example, the use of pellets instead of a powder.

If prevention to exposure or substitution is not practicable, then the exposure rates MUST be controlled. The following measures should be used:-

  • Use work processes, systems and engineering controls that will minimize the materials that are used/produced and use equipment that can totally enclose the process.
  • Control exposure at its source (e.g. exhaust ventilation), reduce the duration of the exposure and reduce the quantities of the hazardous chemical/substance.
  • Provide personal protective equipment (PPE). This should be seen as a last resort and should never be used in place of any control measures that have been set up. Therefore PPE should only be used as PART of your controls.
  1. Set up exposure control measures and ensure that they are followed:- 

COSHH requires that employees make proper use of control measures and that any defects are reported without delay.

Therefore staff should be given adequate training to ensure that they understand the control measures. Suitable supervision must be available when these measures are being carried out.

The control measures MUST be maintained to ensure that each significant element of the measures works as it was originally intended to work. For example, if respiratory equipment was to be used, then this equipment must be checked at regular intervals.

  1. Monitor Exposure:- 

Under COSHH you must measure the concentration of  hazardous substances in the air breathed in by your workers where your assessment concludes that:-

  • There could be serious risks to health if control measures failed.
  • The exposure limits could be exceeded.
  • Control measures are not working. 

However you do not need to do this if you can show by   evaluation that you are preventing or controlling exposure by a system that sounds an alarm if hazardous substances are detected. The COSHH ACOP provides examples of other alternatives of evaluation.

Air monitoring must be carried out when employees are exposed to substances and processes specified under schedule 5 of the COSHH regulations ( UK).

Monitoring records should be kept for 5 years. If health surveillance is carried out, then monitoring reports are to be kept with medical surveillance records.

  1. Carry out appropriate health surveillance:- 

COSHH requires that health surveillance be conducted in these circumstances:-

  • Where an employee is exposed to a substance listed in Schedule 6 of COSHH (see below)
  • Where employees are exposed to a substance linked to a particular disease or adverse health effect and there is a reasonable likelihood, under the conditions of the work, of that disease or effect occurring, and it’s possible to detect the disease or health effect.

Schedule 6


Substance for medical Surveillance                    Process

Vinyl chloride monomer. In manufacture, production, reclamation, storage, discharge, transport, use or polymerisation.
Nitro or amino derivatives of phenol and benzene or its homologues. In the manufacture of nitro or amino derivatives of phenol and of benzene or its homologues and the making of explosives with the use of any of these substances.
Potassium or sodium chromate or dichromate. In Manufacture.
Ortho-toluidine and its salts.Dianisidine and its salts.Dichlorobenzidine and its salts. In manufacture, formation or use of any of these substances.
Auramine. Magenta. In manufacture.
Carbon disulphide. Disulphur dichloride. Benzene, including benzol.Carbon tetrachloride. Trichloroethene. Processes in which these substances are used, or given off as vapour, in the manufacture of India rubber or its articles or goods made wholly or partly of India rubber.
Pitch. In manufacture of blocks of fuel consisting of coal, coal dust, coke or slurry with pitch as a binding substance.


Health surveillance may involve examination by a doctor or trained nurse. In some cases trained supervisors could check the employee’s skin for dermatitis or ask questions about breathing difficulties.

  1. Prepare plans and procedures to deal with accidents, incidents and emergencies:- 

Where the work activity gives rise to the risk of an accident, incident or emergency involving expose to a hazardous substance which goes well beyond the normal day to day work.

In these circumstances, your response must be planned before any emergency involving hazardous substances.

Setting up a procedure where warning and communication systems are in place to enable an appropriate response immediately after any incident occurs, and to ensure that information on emergency arrangements is available to those who need to see it. This includes the emergency services, and these procedures need to be practiced at regular intervals.

If any accident/incident occurs, you must ensure that immediate steps are carried out to minimize the harmful effects and restore the situation to normal.

Only trained staff are to remain in any emergency area and only if they have been issued with the appropriate safety equipment. 

  1. Ensure employees are trained, informed & supervised. 

COSHH requires that employees are provided with suitable information, instruction and training, which could include:-

  • Names of substances they work with or could be exposed to and access to the Material Safety Data Sheets.
  • The findings of a risk assessment.
  • Training on how they can protect themselves (and others).
  • How to check and use any Personal Protective Equipment that has been issued to them.
  • The results of any exposure monitoring and or health surveillance without divulgence of employee names. (They are allowed access to their own records).
  • Emergency procedures that must be followed.

The training, information and instruction should be updated and adapted to any changes in the type of work or the methods of work. When this is done, the information must be passed on to the staff and understood by all employees.

The previous 8 requirements are critical. Your employees MUST understand the risks involved and fully understand the steps and control measures to be taken to reduce these risks.



Chemical Analysis
Image showing a coshh assessment for ordinary cement