# A petrol station uses earthing cables to prevent sparking when fuel is being transferred between tankers and underground storage tanks. Explain why static charge can build up during fuel transfer and why sparking is dangerous in this situation, and describe how earthing prevents a spark from occurring.

> OCR A-Level Physics A (H556) — 3.2 Forces in action · Explain · 5 marks

> During fuel transfer at a petrol station, fuel flows through pipes at high speed. Engineers attach a metal earthing cable between the tanker and the ground before any fuel is transferred.

## Mark scheme (5 marks)

1. Electrons are transferred between the fuel and the pipe walls as fuel flows through, causing a charge imbalance / static charge to build up on the tanker.
2. The tanker is made of metal but is insulated from the ground by rubber tyres, so the charge cannot flow away and continues to build up.
3. If enough charge builds up, a spark can occur as charge jumps through the air between the highly charged tanker and a nearby object of opposite / lower charge.
4. Sparking is dangerous because the spark can ignite the fuel vapour, causing a fire or explosion.
5. The earthing cable provides a low resistance path for electrons to flow from the tanker to the ground, safely removing the excess charge before it can build up enough to cause a spark.

## Key terms

- [static charge](https://www.gradenine.co.uk/glossary/static-charge)
- [sparking](https://www.gradenine.co.uk/glossary/sparking)
- [earthing](https://www.gradenine.co.uk/glossary/earthing)

## Related

- [Revision notes for OCR A-Level Physics A (H556)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/a-petrol-station-uses-earthing-cables-818406cc) · Published by Druglandscape Ltd.