The Fume Cupboard That Wasn't Quite Working
It is Tuesday afternoon in a school laboratory. A Year 11 student, Priya, is preparing to dilute 50 mL of concentrated hydrochloric acid for a titration practical. The fume cupboard's airflow indicator shows a green light, but Priya notices the sash is raised to about 45 cm - well above the marked safe line at 20 cm. Her teacher is in the storeroom. A classmate, Tom, says the green light means it's fine and tells her to hurry up because the class is waiting. Priya also sees that the waste bottle for acid waste is almost full, and the spill kit in the corner has no lid on it. The practical must be finished in 20 minutes before the room is used by another class.
1. Identify the hazards Priya faces and explain what she should do before beginning the dilution.
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Hazards identified:
- Concentrated HCl - corrosive, produces irritating vapour; dilution is exothermic and can spatter.
- Sash position - raised to 45 cm, above the 20 cm safe line. The green light only confirms airflow, not that the sash is at a safe working height. Vapour containment is compromised.
- Full acid waste bottle - risk of overflow and spill when adding more waste.
- Uncovered spill kit - contents may be contaminated, degraded, or incomplete; not ready for immediate use.
- Time pressure and peer pressure - rushing increases error and exposure risk.
What Priya should do:
- Lower the sash to the marked line (or below) before handling the acid.
- Stop and locate the teacher - she should not begin work with a compromised setup and no supervisor present.
- Report the full waste bottle and uncovered spill kit so they can be replaced or sealed before work starts.
- If the teacher cannot attend, the practical should be postponed. A 20-minute deadline does not justify proceeding with multiple unresolved hazards. Priya should also politely decline Tom's pressure - the green light is not a licence to skip the other checks.
2. Explain the correct technique for diluting the concentrated acid once the hazards are resolved, including the order of addition and why.
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Order of addition: Add acid to water, slowly, with stirring - never water to acid.
Reasoning: Dilution of concentrated HCl is strongly exothermic. If water is added to concentrated acid, the small amount of water can boil rapidly from the local heat, causing the acid to spatter out of the vessel. Adding acid slowly to a larger volume of water distributes the heat through the water and keeps the temperature rise manageable.
Procedure:
- Wear splash goggles, lab coat, and nitrile gloves; work with the sash at the marked line.
- Measure the required volume of water into a beaker first (most of the final volume).
- Add the concentrated acid in small portions down the side of the vessel or onto a stirring rod, stirring gently between additions.
- Allow the solution to cool, then make up to the final volume.
- Label the prepared solution immediately with name, concentration, date, and hazard symbols.
- Neutralise or dispose of any residue into the correct acid waste container - only after confirming it has capacity.
3. The spill kit has no lid. Explain why this matters and how it should be managed under workplace health and safety expectations.
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An uncovered spill kit is a control measure that cannot be relied upon. Contents such as absorbent granules can absorb moisture from the air and lose effectiveness; neutralising agents can degrade; items can be removed and not replaced; and the kit may become contaminated with dust or chemical residue. If a spill occurs, the responder may find the kit unusable - turning a minor spill into a serious exposure incident.
Management:
- The kit should be sealed, its contents checked against a checklist, and any missing or degraded items replaced.
- It should be stored in a known, accessible location and inspected on a regular schedule (e.g. termly), with the inspection recorded.
- This is a hazard-reportable defect: Priya should report it through the school's hazard reporting process so it is fixed, not just noted.
- Until the kit is restored, work with concentrated acid should not proceed in that area, because the emergency control is not in place.