How to Write a Risk Assessment for a Chemistry Practical

A risk assessment is the thinking you do before an experiment to make sure nobody gets hurt. In a professional lab it’s a legal requirement; in schools it’s a core practical skill and often an assessed one. Done well, it isn’t a box-ticking exercise. It’s a short, clear plan that makes the experiment safer and makes you a better scientist.

This guide explains the key ideas, gives a step-by-step method, and shows a complete worked example.

Hazard vs risk

These two words are often confused, but they mean different things:

• A hazard is something with the potential to cause harm. Concentrated sulfuric acid is a hazard. So is a Bunsen flame.
• A risk is the likelihood that harm will actually happen, combined with how serious it would be.

A hazard can be high while the risk is low. Concentrated sulfuric acid is very hazardous, but if a teacher dispenses a small amount into a dilute solution inside a fume cupboard, wearing goggles and gloves, the risk is low. Good control measures turn big hazards into small risks.

The five steps

Step 1: list every chemical, piece of equipment and process

Include:

• all chemicals, with their concentrations (starting materials, products and by-products)
• equipment that can cause harm (glassware, heat sources, sharp objects, electrical equipment)
• processes (heating, filtering, distilling, handling gases)

Step 2: identify the hazards

For each chemical, find its hazards from the label, a hazard data source provided by your school, or the safety data sheet (SDS). Record the relevant GHS hazard category: corrosive, irritant, flammable, toxic, oxidising, and so on.

For equipment and processes, think about burns, cuts, scalds, fire, electric shock and splashing.

Step 3: decide who could be harmed and how

Think about the route of harm:

• eyes (splashes, fumes)
• skin (burns, irritation, absorption)
• inhalation (gases, vapours, dust)
• ingestion (contaminated hands, food)

And think about who: you, your partner, others nearby, the technician who clears up.

Step 4: choose control measures

Control measures reduce the risk. A useful order to think in is the hierarchy of control, from most to least effective:

1. Elimination: can you avoid the hazard altogether? (Use a different, safer reaction.)
2. Substitution: can you use a less hazardous chemical or a lower concentration? (0.5 mol/dm³ instead of 2 mol/dm³ acid.)
3. Engineering controls: fume cupboards, safety screens, electric heaters instead of flames.
4. Administrative controls: procedures, supervision, small quantities, training.
5. Personal protective equipment (PPE): eye protection, gloves, lab coats.

PPE is essential, but it’s the last line of defence, not the first. The best risk assessments reduce hazards before relying on goggles.

Step 5: plan for emergencies and disposal

• What should you do if the chemical gets on skin or in eyes, is spilled, or catches fire?
• How should waste be disposed of? (Down the sink with plenty of water, into a labelled residue container, or returned to a technician?)

A useful table format

Hazard (substance or activity)	Hazard type	Risk (how harm could happen)	Control measures	In an emergency

Keep entries specific. “Wear goggles” is a control measure; “be careful” is not.

Worked example: titrating sodium hydroxide with hydrochloric acid

Experiment: 25.0 cm³ of about 0.1 mol/dm³ sodium hydroxide is titrated with 0.100 mol/dm³ hydrochloric acid using phenolphthalein indicator. See acid–base titration.

Hazard	Hazard type	Risk	Control measures	In an emergency
Sodium hydroxide, 0.1 mol/dm³	irritant to eyes and skin at this concentration (more concentrated solutions are corrosive)	splashes when filling the pipette or burette; eye damage	eye protection throughout; use a pipette filler; fill burette below eye level with a funnel; wipe up drips	eye: rinse at eyewash 10–15 min, tell teacher; skin: rinse with water
Hydrochloric acid, 0.100 mol/dm³	low hazard at this concentration; may irritate eyes	splashes	eye protection; take care when filling the burette	rinse with water
Phenolphthalein indicator	contains ethanol (flammable); phenolphthalein is a possible carcinogen	fire if near a flame; skin contact	no flames nearby; use dropper bottle; small volumes; wash hands after	rinse skin with water
Glass burette and pipette	cuts if broken	breakage when clamping or filling	clamp securely; don’t overtighten; report and clear breakages with brush and dustpan	first aid for cuts; report
Standing to fill burette	spills into eyes	filling above head height	lower the burette or remove from clamp to fill	as above

Disposal: the neutral sodium chloride solution containing a trace of indicator can be poured down the sink with plenty of water, unless local rules say otherwise.

Worked example: heating copper carbonate

Experiment: Heating a small amount of copper(II) carbonate in a test tube and testing the gas with limewater.

Key points a good risk assessment would include:

• Copper(II) carbonate: harmful if swallowed and toxic to aquatic life → small quantities, avoid raising dust, wash hands, dispose of solid residue in the designated container rather than the sink.
• Heating a test tube: suck-back of limewater into a hot tube can crack the glass → remove the delivery tube from the limewater before stopping heating.
• Bunsen burner: burns and fire → tie back hair, use a heatproof mat, safety flame when not heating.
• Limewater (calcium hydroxide solution): irritant to eyes → eye protection.
• Test tube bumping: point the tube away from people.

This example shows why you need to think about processes, not just chemicals. Suck-back is a hazard that only appears from the way the apparatus is used.

Common weaknesses in student risk assessments

• Missing concentrations. “Hydrochloric acid: corrosive” is only true for concentrated solutions. Always state the concentration.
• Vague controls. “Be careful” or “use safety equipment” aren’t specific. Say which equipment and how.
• Only listing chemicals. Heat sources, glassware and processes such as heating or gas collection need assessing too.
• Forgetting products. A reaction might produce a toxic gas (such as sulfur dioxide or chlorine) even if the starting chemicals are fairly safe.
• No emergency or disposal plan.
• Relying only on PPE. Consider lower concentrations, smaller scales or a fume cupboard first.

Where to find hazard information

• The label on the container, with its GHS pictograms and H- and P-statements.
• Safety data sheets (SDS) from the supplier.
• School or college guidance from national safety advisory bodies (for example, CLEAPSS in the UK and similar organisations elsewhere), which give hazard information specifically for school quantities and concentrations.

Key takeaways

• A hazard is the potential for harm; risk is how likely and how serious the harm would be.
• List every chemical (with concentration), piece of equipment and process, then identify hazards and routes of harm.
• Choose control measures using the hierarchy: eliminate, substitute, engineer, organise, then protect.
• Be specific, include emergency actions and disposal, and consider products as well as reactants.
• Follow the general rules in lab safety rules.