A manufacturer of fire extinguishers previously used halon gases in their products. Explain why halons were considered harmful to the environment and describe what happened internationally to address this problem.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Halon gases were widely used in fire extinguishers and fire suppression systems throughout the twentieth century. Like CFCs, halons contain halogen atoms bonded to carbon atoms.
Model answer (5 marks)
Halons, like CFCs, release bromine or chlorine atoms in the stratosphere when they break down. These halogen atoms act as catalysts, destroying ozone molecules and thinning the ozone layer. A thinner ozone layer allows more UV‑B radiation to reach the Earth's surface, which increases the risk of skin cancer and damages ecosystems. Internationally, the problem was tackled by the Montreal Protocol, which phased out the production and use of halons and other ozone‑depleting substances.
Examiner tips
- Use the exact terms ‘bromine or chlorine atoms’, ‘catalytically destroy ozone’, ‘thin the ozone layer’, ‘increased UV‑B radiation’, and ‘Montreal Protocol’
- Show the causal chain: halons → halogen atoms → ozone destruction → more UV → harm
- Mention the phase‑out/ban aspect of the Protocol
Common mistakes
- Confusing halons with CFCs only, ignoring the bromine component
- Failing to link ozone depletion to increased UV radiation and its biological effects
- Not naming the Montreal Protocol or describing its purpose
Mark scheme (5 marks)
- Halons (like CFCs) release halogen/bromine or chlorine atoms/radicals in the stratosphere
- These halogen atoms/radicals catalytically destroy ozone molecules
- This thins/depletes the ozone layer, allowing more UV radiation to reach Earth's surface
- Increased UV radiation reaching Earth causes harm to living organisms, e.g. increased risk of skin cancer or damage to ecosystems
- International agreements (such as the Montreal Protocol) were made to phase out/ban the use of CFCs and halons
Key terms in this question
Related
- All OCR A-Level Chemistry B: Salters (H433) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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