Combustion Without a Laboratory: Kerosene, Smoke, and 58 Students
Bikash Yadav teaches Grade 8 science at a school in Birgunj, Madhesh. The school has a small laboratory room with 12 stools, a cupboard holding a few test tubes and a spirit lamp, no gas supply, and no fume hood. He must teach the unit on combustion and fuels to 58 students across two sections. The curriculum expects a demonstration that a candle needs air and a discussion of fuels used at home. Every afternoon, waste is burned in an open pit about 30 metres from the classrooms, and students complain of coughing; most families use firewood or kerosene. A student has offered to bring kerosene from home so the class can burn it. The first-aid box is stocked, but the extinguisher was last inspected four years ago and there is no tap near the laboratory. Two students in one section have asthma.
1. Assess the kerosene proposal and decide. Then design a safer practical that still teaches that burning needs air, using only what the school has.
Read the worked answer
Risk assessment of the kerosene proposal
Hazards: kerosene gives off flammable vapour at ordinary room temperature and produces a hot, smokeless flame that is hard to see in daylight; a spill or a tipped container can spread burning liquid. Controls needed would be a fire blanket, a suitable dry-powder or foam extinguisher, a ventilated space, eye protection, a defined safe distance, and trained supervision. The school has none of these in working order: the extinguisher is four years past inspection, there is no water point, and 58 students cannot be kept at a safe distance in a 12-stool room. Decision: refuse the open burning of kerosene as a class activity. Record the reason and tell the student why, publicly enough that the refusal is understood as safety, not distrust.
Safer alternative
- Teacher-only flame: a short candle fixed upright on a metal tray, lit at the front of a cleared bench, with a bucket of sand and a damp cloth within reach, hair tied back, no loose sleeves, windows open.
- Student investigation in groups of four: lower a small glass jar over the candle and time how long the flame lasts; repeat with the jar raised on two small stones so air can enter. Students record times in a table - this is the data, not the fire.
- Teacher demonstration of carbon dioxide from baking soda and vinegar poured over a candle in a beaker, only if the beaker is tall and the candle is small.
- Students with asthma sit near the door and take the timer and recorder roles; no student is closer than two metres to the flame.
Closing the loop: discuss why kerosene is still used at home and what ventilation and storage would require - the safety lesson is the content, not an interruption to it.
2. Turn the open-pit waste burning into a two-week investigation that connects combustion, health, and civic action, within two periods a week and no budget.
Read the worked answer
Purpose: the burning pit is a local example of incomplete combustion, so it teaches the chemistry and gives a legitimate route into civic awareness without extra money.
Week 1 - evidence
- Lesson 1: what complete and incomplete combustion produce, and why carbon monoxide and soot particles matter for lungs. Students link this to the smell and the coughing reported at school.
- Fieldwork, done in small groups at times when the pit is not actively burning (never walk into smoke): mark on a sketched map where the pit is relative to the classrooms and the water point, estimate the distance by pacing, and count visible waste types from a safe distance.
- Homework-free survey: a five-question tally in the neighbourhood - how many households burn waste, how often, which fuels are used for cooking, and whether anyone reports coughing. Simple tally marks, no printing needed; students copy the table into their exercise books.
Week 2 - explanation and action
- Lesson 2: collate the tallies on the board, calculate simple fractions of households burning waste, and compare with the class data on coughing. Discuss correlation and caution about causation.
- Lesson 3: students draft a one-page letter to the ward office describing the pit, distance, frequency, and the class's evidence, and propose a covered bin or a fixed collection day. Send it with the head teacher's signature and present the findings at assembly.
Assessment: the tally table, the diagram of the pit and classrooms, and a short written explanation of why incomplete combustion is more harmful than complete combustion. Roles are assigned so that no student needs to buy materials or approach the smoke.
3. How should Bikash make the practical inclusive and still assess learning meaningfully for 58 students? Give concrete arrangements and a rubric.
Read the worked answer
Inclusion arrangements
- Seat the two students with asthma near the door on the windward side; give them the timer, data recorder and reporter roles so their participation is substantive, not a consolation.
- Keep the flame at the front with a two-metre clear zone, and run the candle test as a rotating group activity with four students at a time while the other groups complete a data-interpretation task at their benches. Fifty-eight students cannot all watch a small flame at once, so rotation is a safety measure as well as a management one.
- No student is required to bring anything from home; the jar, candle, tray, sand bucket and damp cloth are teacher-supplied.
- Allow a written alternative for any student who does not wish to be near a flame.
Assessment rubric (four criteria, four levels each)
- Explanation: states that burning needs oxygen and describes the evidence from the jar test.
- Data: records times accurately and compares the two jar conditions.
- Safety: identifies two hazards and the control used for each.
- Communication: presents the group's finding in one clear paragraph or oral report.
Why this works: it assesses the concept, not the ability to stand near a fire. Oral reporting is legitimate evidence for students whose writing is weak, and the safety criterion makes the practical's constraints part of the content. Keep the same rubric across both sections so the marks are comparable, and sample-check three groups per section rather than marking every group's discussion.