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The following risk assessment is a suggestion only; it is the one that I use, but it may not be suitable for your institution, and I accept no responsibility for its use elsewhere. You are responsible for your risk assessments, not me!


Making a Risk Assessment

Health and Safety Regulations currently in force require that every experiment done shall have associated with it a Risk Assessment (RA); the object of this assessment is the elimination or the adequate control of risks to health. It is not the purpose of the Regulations or this assessment regime to prevent experimentation – partly it is to assist in chemical education, as well as to discharge statutory responsibility properly.

The RA must consider the intrinsic hazard associated with the materials used, and the exposure potential under the proposed conditions of use. It is therefore an analysis of an operation, so that procedures using hazardous materials may be acceptable if the exposure is sufficiently low. The age of the pupils concerned is a further consideration, so that some procedures would be inappropriate for 5th formers yet acceptable for a 6th form.


Hazard evaluation. The hazard associated with a substance is its potential to impair health. Some degree of hazard can be ascribed to almost any substance, whilst for some the toxicity or the harmful effects are not fully known.

Substances which are likely to be hazardous are those which are

  • very toxic
  • toxic
  • harmful
  • corrosive
  • irritant


  • which have a maximum exposure limit (MEL) or
  • which have an occupational exposure standard (QES) or
  • which may produce dusts in appreciable concentration (typically 10 mg m-3 total inhalable dust).

Hazard categories will be used to help the Hazard evaluation:

Hazard category Hazard classification
Extreme (none kept)
High Very toxic: toxic: defined MEL or OES: substances with unknown toxicity.
Medium Harmful: irritant: corrosive
Low Substances not matching criteria for hazard labelling.

Each substance to be used should be checked and its hazard category noted on the RA sheet for the proposed experiment.


Exposure estimation. Hazardous substances vary enormously in potency. A substance with a high hazard may present an acceptably small risk if the exposure potential is low. Conversely, unacceptable risks may result from high exposures to substances with low hazard.

Factors to be taken into account in evaluating exposure potential relate to both substance and activity, and may include

  • Substance:
quantity used
physical form and properties
concentration if in solution
  • Activity:potential for exposure (e.g. production of aerosol)
route of exposure (dermal, inhalation, ingestion)
frequency and duration of activity


A small scale of working is to be preferred wherever possible. Other factors listed above have to be taken in to account and require professional judgement. The normal basis for estimating exposure potential is to be the matrix below.


Typical basis for estimating exposure potential.






A: Quantity of substance less than 1 g 1 to 100 g more than 100 g
B: Physical character of substance dense solids: non- volatile liquids: no skin absorbtion. Dusty or lyophilised solids; volatile liquids; low skin absorbtion. Gases; highly volatile liquids; aerosols; solutions that promote skin absorbtion.
C: Characteristics of operation or activity. Predominantly enclosed system, low chance of mishap. Partially open system, low chance of mishap. No physical barrier, any operation where chance of mishap is medium or high.

The exposure potential is estimated by multiplying A x B x C:

ABC < 1000: LOW exposure potential

1000< ABC< 10000: MEDIUM exposure potential

10000 < ABC: HIGH exposure potential.

Time factors such as the frequency and duration of an activity should be considered. Short duration tasks involving a few seconds exposure at infrequent intervals should not affect the initial estimate; continuous operations on a daily basis would probably raise the estimate to the next higher category.

The RISK ASSESSMENT is then made using the matrix below, and a containment regime arrived at.

Matrix for evaluation of risk assessment and control determination.

Risk = Hazard x Exposure potential.

Hazard Category Extreme Risks presented by such substances are unsuited to this procedure and must be addressed on an individual basis.
















Exposure potential


Containment regime:

1 Open bench

2 Fume cupboard or other specially vented area

3 Special facility. This is not available, so experiments falling in this category are not to be carried out.

The appropriate containment regime must be selected, or the experiment modified until its Risk is acceptable.



For standard experiments an RA will be prepared and kept in the folders provided. The existence of such an RA does not absolve staff from the responsibility to ensure that the risk associated with a particular experiment has been identified and is acceptable.

If appropriate the hazard category of substances used, and the containment regime and precautions to be observed, must be given on any worksheet and be reinforced orally before the experiment is performed. Students should be encouraged to include RA as part of their planning of experiments.


Sources of information:

Information on the hazards associated with particular substances can be found in the BDH Hazard Handbooks. In addition Health and Safety issues in a broader sense should comply with the criteria given in Croner’s Manual for Heads of Science.

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