Risk assessment

Under COSHH (Control Of Substances Hazardous to Health) regulations it is a legal requirement to make a suitable assessment of hazards and how to minimize them when dealing with dangerous materials. Your teacher/lecturer will have done such assessments for your regular experiments, but you must do an assessment, and have it checked, if you are designing your own experiment. You can see a suitable risk assessment form here or print one out here (Word document).

The principle behind these assessments is to recognize and minimize any risks. We start by briefly describing the procedure involved in our proposed experiment. There may be some non-chemical hazards here. For example, if we need to use a hot oven then there is a risk of burns. The control measure is the action we take to try to reduce, or eliminate, the risk. In the last example we might suggest the use of heat proof gloves when using the oven.

We then need to consider any hazardous chemicals that we intend to use or any which might be produced during the experiment. We then look for up to any hazard data. This may come out of a book like the BDH Hazard data sheets or from a set of cards such as the Hazcards provided by CLEAPSS. Ask your teacher or technician if these are available for your use. Don't just copy the cards, but adapt them to your experiment. Some cards deal with a number of different chemicals. Make sure you do not copy down risks associated with a chemical which you are not using.

If you have access to the Internet this also can supply useful information, although it often has an American slant. The following site was available at the time of writing: University of Akron. A limited set of hazard data can be found on this disk here.

Highly flammable hazard sign

Having located the hazards, we see if they can be reduced by using safer alternative materials. If not, we need to assess what control measures will be needed. This may be the use of suitable protective clothing (like gloves) or limiting the quantity of material to be used. Hazardous powders should be handled carefully to avoid raising any dust. Oxidizing agents can be dangerous when mixed with reductants - the hazard data should indicate any hazardous combinations. We can make use of an electric heating mantle or a water bath to reduce the risk of fire. Many organic chemicals are highly flammable. A fume cupboard is essential where dangerous gases or hazardous organic vapours are generated in the experiment.

The estimated quantities need only be very approximate, like (about) 10 grams. We need to state the quantity as the risk and consequent control measures are dependent on the quantity. Whether we use 1 cm³ or 1000 litres of cyclohexane, the basic hazard is the same - it is highly flammable. However, the risk and the precautions we would need to take would be very different in these two cases.

Flammable liquids are hazardous

Finally, we shall have to decide how to dispose of the waste from the experiment. Small quantities of low hazard, water soluble waste can be washed down the sink with plenty of water. Certain substances like immiscible organic liquids will probably have a collection bottle provided by your technician. Waste silver salts may also be collected. How these are subsequently disposed of need not concern you for the purposes of risk assessment. They will probably be collected by a professional chemical waste disposal company. Advice on disposal is provided with the hazard data source. If you are unsure check with your teacher or technician.

Using the above form try to write a risk assessment for the oxidation of propan-1-ol to propanoic acid. This uses an oxidizing mixture of sodium dichromate and concentrated sulfuric acid and will need refluxing. You can find a suitable completed risk assessment form here.