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Using hazardous substances safely

Guidance for managers and supervisors who work with (or have employees or students who work with) hazardous substances.



The University's hazardous substances safety standard aims to identify significant risks posed to the health or safety of anyone who could potentially be affected by working with hazardous substances, by carrying out suitable and sufficient risk assessments of all hazardous substance use, storage, handling and disposal.

The significant findings of these assessments are used to identify control measures to eliminate risks to employees and others. Where elimination is not reasonably practicable, other control measures are introduced to reduce the risk of exposure to a tolerable level, and in any case, below any identified Workplace Exposure Limit (WEL).

This guidance supports the standard by describing the process to enable employees to carry out risk assessments in accordance with the relevant legislation: Control of Substances Hazardous to Health (COSHH) Regulations 2002.

Hazardous substances

A hazardous substance is any substance which can − under some circumstances − have a harmful effect on a person’s health. This includes chemicals, products containing chemicals, fumes, dusts, vapours, mists, nanomaterials, gases including asphyxiate gases, biological agents and germs that can cause disease.

Hazardous substances are not confined to laboratories and may be used in a variety of activities including cleaning, maintenance (such as painting), dust generating tasks in workshops and use of oils, lubricants and adhesives.

Some hazardous substances have Workplace Exposure Limits (WELs). These are British occupational exposure limits and are set in order to help protect the health of workers. They are intended to prevent excessive exposure to specified hazardous substances by containing exposure below a set limit. WELs are concentrations of hazardous substances in the air, averaged over a specified period of time, referred to as a time-weighted average (TWA).

Two time periods are used:

  • long-term (eight hours), and

  • short-term (15 minutes)

Short-term exposure limits (STELs) are set to help prevent effects such as eye irritation, which may occur following exposure for a few minutes.

They are listed in HSE publication EH40 Workplace Exposure Limits 2005.

Date of last review: March 2023 (with the University's Hazardous Substances Policy) Date of next review: March 2025

COSHH Risk Assessment

A COSHH Risk Assessment is a risk assessment that concentrates on the hazards and risks from substances in the workplace.

It needs to be completed by a 'competent person' − a person with adequate knowledge, training and expertise. For example, in the design of processes, control measures including ventilation and PPE, the human and technical reasons why control measures can fail, and the importance of following the principles of good practice for the control of substances hazardous to health.

The following principles of good practice are defined in in Schedule 2A of the COSHH Regulations. They must all be applied to obtain effective and reliable control:

  • minimise emission, release and spread

  • consider routes of exposure

  • choose control measures proportionate to the risk

  • choose effective control options

  • personal protective equipment – the final control option

  • review the effectiveness of controls

  • provide information and training

  • new measures, new risks

The risk assessment needs to be suitable and sufficient:

  • it should be reflective of the scale of the work being carried out

  • all significant hazards should be identified and proportional control measures applied to reduce the risk to a tolerable level

  • it should be clear and straightforward to understand

The risk of harm needs to be reduced to a level that is ‘as low as is reasonably practicable'

This means:

  • all control measures are in good working order

  • exposures are below the Workplace Exposure Limit, where one exists

  • exposure to substances that cause cancer, asthma or genetic damage is reduced to as low a level as possible

COSHH risk assessment process

The Health and Safety Executive (HSE) provide the following guidance on completing a COSHH assessment at HSE.

Gather information about the substances, the work and the working practices

1) Visit the workplace.

2) Involve employees.

3) Consult Safety Data Sheets/Incident records.

4) Consider all routes of exposure:

  • inhalation − breathing in fumes, vapours, dust

  • ingestion − transfer from hand to mouth

  • skin contact − contact with contaminated item

  • Skin puncture − needle-stick injury, cuts

  • eye exposure − splash, fume, dust

5) Who could be affected and how? For example, is the substance a carcinogen, mutagen or a cause of occupational asthma or other occupational disease?

Evaluate the risks to health

  • What is the potential of a substance to cause harm (for example, the hazard)?

  • What is the chance of exposure occurring?

  • How often is exposure liable to occur?

  • What levels will people be exposed to and for how long?

Identify necessary control measures in accordance with the 'hierarchy of controls'

  • Eliminate

  • Substitution

  • Apply principles of good control practice

Control exposure to carcinogens and mutagens

1) More stringent control required due to health effects:

  • prevention

  • adequate control

  • use, storage, labelling and disposal

  • precautions against contamination

2) Provision of suitable PPE, particularly in event of an uncontrolled release.

Control exposure to biological agents

Take into consideration:

  • deliberate work

  • incidental exposure

  • immunisation

Record the assessment and provide information on significant risks to all persons potentially affected

  • Required by law

  • Needs to be suitable and sufficient

  • Readily accessible to all users

Review the assessment

  • If assessment no longer valid

  • If there are significant changes to the work activity

  • On a regular basis: recommended review intervals are annually for High Risk Activities (such as lab work) and every three years for Low Risk Activities (such as cleaning)

Provide suitable and sufficient information, instruction and training

  • Details of hazardous substances liable to be exposed to

  • Significant findings of COSHH Assessment

  • Appropriate precautions and actions to be taken

  • Use and importance of hygiene facilities

  • Results of any exposure monitoring

  • Results of Collective Health Surveillance (data privacy)

  • Maintain records of training

Generate incident response arrangements

  • Identification of hazardous substances including use, estimated amounts, storage

  • Foreseeable types of incidents such as spills, uncontrolled release, exothermic reaction, exceedance of a WEL

  • Safety equipment required including Personal Protective Equipment (PPE) and Respiratory Protective Equipment (RPE)

  • Provision of First Aid facilities

  • Roles and responsibilities of employees

  • Procedures for clean-up and waste disposal

Roles and responsibilities for working safely with hazardous substances are set out in the University's hazardous substances safety standard.


If you have any questions, please contact us.

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